101
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Aberrant regulation of superantigen responses during T-cell reconstitution and graft-versus-host disease in immunodeficient mice. Blood 2002. [DOI: 10.1182/blood.v100.6.2216.h81802002216_2216_2224] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Acute graft-versus-host disease (GVHD) after allogeneic stem cell transplantation is associated with impaired deletion and anergy of host-reactive T cells. To elucidate the immunoregulatory events that may contribute to such dysregulated T-cell responses in GVHD, we studied superantigen (SAg) responses after adoptive T-cell transfer into severe combined immunodeficient (SCID) mice. SAg responses are normally regulated by mechanisms involving deletion and anergy, with SAg-reactive T cells typically being deleted rapidly in vivo. In a SCID mouse model of GVHD, however, allogeneic host SAg-reactive T cells were not deleted rapidly, but rather persisted in increased numbers for several months. Moreover, depending on the timing of SAg stimulation and the numbers of T cells transferred, dysregulation (impaired deletion and anergy) of SAg responses could be demonstrated following the adoptive transfer of syngeneic T cells into SCID mice as well. Transgenic T-cell receptor-bearing KJ1-26.1+ T cells were then used to determine the fate of weakly reactive T cells after adoptive transfer and SAg stimulation. When transferred alone, KJ1-26.1+ T cells demonstrated impaired deletion and anergy. In the presence of more strongly staphylococcal enterotoxin B (SEB)–reactive T cells, however, KJ1-26.1+ T cells were regulated normally, in a manner that could be prevented by inhibiting the effects of more strongly SEB-reactive cells or by increasing the level of activation of the KJ1-26.1+ T cells themselves. We suggest that the control mechanisms that normally regulate strongly activated T cells in immunocompetent animals are lost following adoptive transfer into immunodeficient hosts, and that this impairment contributes to the development of GVHD.
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102
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Torres BA, Perrin GQ, Mujtaba MG, Subramaniam PS, Anderson AK, Johnson HM. Superantigen enhancement of specific immunity: antibody production and signaling pathways. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 169:2907-14. [PMID: 12218104 DOI: 10.4049/jimmunol.169.6.2907] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Superantigens are microbial proteins that induce massive activation, proliferation, and cytokine production by CD4+ T cells via specific Vbeta elements on the TCR. In this study we examine superantigen enhancement of Ag-specific CD4+ T cell activity for humoral B cell responses to T-dependent Ags BSA and HIV gp120 envelope, type I T-independent Ag LPS, and type II T-independent Ag pneumococcal polysaccharides. Injection of BSA followed by a combination of superantigens staphylococcal enterotoxin A and staphylococcal enterotoxin B (SEB) 7 days later enhanced the anti-BSA Ab response in mice approximately 4-fold as compared with mice given BSA alone. The anti-gp120 response was enhanced approximately 3-fold by superantigens. The type II T-independent Ag pneumococcal polysaccharide response was enhanced approximately 2.3-fold by superantigens, whereas no effect was observed on the response to the type I T-independent Ag LPS. The superantigen effect was completely blocked by the CD4+ T cell inhibitory cytokine IL-10. SEB-stimulated human CD4+ T cells were examined to determine the role of the mitogen-activated protein (MAP) kinase signal transduction pathway in superantigen activation of T cells. Inhibitors of the mitogen pathway of MAP kinase blocked SEB-induced proliferation and IFN-gamma production, while an inhibitor of the p38 stress pathway had no effect. Consistent with this, SEB activated extracellular signal-regulated kinase/MAP kinase as well as MAP kinase-interacting kinase, a kinase that phosphorylates eIF4E, which is an important component of the eukaryotic protein synthesis initiation complex. Both kinases were inhibited by IL-10. Thus, superantigens enhance humoral immunity via Ag-specific CD4+ T cells involving the stress-independent pathway of MAP kinase.
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MESH Headings
- Adjuvants, Immunologic/administration & dosage
- Adjuvants, Immunologic/pharmacology
- Animals
- Antibody Specificity/immunology
- CD4-Positive T-Lymphocytes/enzymology
- CD4-Positive T-Lymphocytes/immunology
- Cells, Cultured
- Enterotoxins/administration & dosage
- Enterotoxins/immunology
- Enterotoxins/pharmacology
- Epitopes, T-Lymphocyte/immunology
- Female
- HIV Antibodies/biosynthesis
- HIV Antibodies/blood
- HIV Envelope Protein gp120/administration & dosage
- HIV Envelope Protein gp120/immunology
- Humans
- Immunity, Cellular/immunology
- Immunoglobulin G/biosynthesis
- Immunoglobulin G/blood
- Injections, Intraperitoneal
- Lymphocyte Activation/immunology
- MAP Kinase Signaling System/immunology
- Mice
- Mice, Inbred C57BL
- Serum Albumin, Bovine/administration & dosage
- Serum Albumin, Bovine/immunology
- Serum Albumin, Bovine/pharmacology
- Superantigens/administration & dosage
- Superantigens/immunology
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Affiliation(s)
- Barbara A Torres
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
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103
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Jones RG, Elford AR, Parsons MJ, Wu L, Krawczyk CM, Yeh WC, Hakem R, Rottapel R, Woodgett JR, Ohashi PS. CD28-dependent activation of protein kinase B/Akt blocks Fas-mediated apoptosis by preventing death-inducing signaling complex assembly. J Exp Med 2002; 196:335-48. [PMID: 12163562 PMCID: PMC2193932 DOI: 10.1084/jem.20020307] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The T cell costimulatory molecule CD28 is important for T cell survival, yet both the signaling pathways downstream of CD28 and the apoptotic pathways they antagonize remain poorly understood. Here we demonstrate that CD4(+) T cells from CD28-deficient mice show increased susceptibility to Fas-mediated apoptosis via a phosphatidylinositol 3-kinase (PI3K)-dependent pathway. Protein kinase B (PKBalpha/Akt1) is an important serine/threonine kinase that promotes survival downstream of PI3K signals. To understand how PI3K-mediated signals downstream of CD28 contribute to T cell survival, we examined Fas-mediated apoptosis in T cells expressing an active form of PKBalpha. Our data demonstrate that T cells expressing active PKB are resistant to Fas-mediated apoptosis in vivo and in vitro. PKB transgenic T cells show reduced activation of caspase-8, BID, and caspase-3 due to impaired recruitment of procaspase-8 to the death-inducing signaling complex (DISC). Similar alterations are seen in T cells from mice which are haploinsufficient for PTEN, a lipid phosphatase that regulates phosphatidylinositol-3,4,5-trisphosphate (PIP(3)) and influences PKBalpha activity. These findings provide a novel link between CD28 and an important apoptosis pathway in vivo, and demonstrate that PI3K/PKB signaling prevents apoptosis by inhibiting DISC assembly.
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Affiliation(s)
- Russell G Jones
- Department of Medical Biophysics, Ontario Cancer Institute, University of Toronto, Canada
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104
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Banz A, Pontoux C, Papiernik M. Modulation of Fas-dependent apoptosis: a dynamic process controlling both the persistence and death of CD4 regulatory T cells and effector T cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 169:750-7. [PMID: 12097377 DOI: 10.4049/jimmunol.169.2.750] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have previously shown that regulatory CD25(+)CD4(+) T cells are resistant to clonal deletion induced by viral superantigen in vivo. In this work we report that isolated CD25(+)CD4(+) T cells activated in vitro by anti-CD3 Ab are resistant to Fas-induced apoptosis, in contrast to their CD25(-)CD4(+) counterparts. Resistance of CD25(+)CD4(+) T cells to Fas-dependent activation-induced cell death is not linked to their inability to produce IL-2 or to their ability to produce IL-10. The sensitivity of both populations to Fas-induced apoptosis can be modulated in vitro by changing the CD25(+)CD4(+):CD25(-)CD4(+) T cell ratio. The sensitivity of CD25(-)CD4(+) T cells to apoptosis can be reduced, while the sensitivity of CD25(+)CD4(+) T cells can be enhanced. Modulation of Fas-dependent apoptosis is associated with changes in cytokine production. However, while CD25(-)CD4(+) T cell apoptosis is highly dependent on IL-2 (production of which is inhibited by CD25(+)CD4(+) T cells in coculture), modulation of CD25(+)CD4(+) T cell apoptosis is IL-2 independent. Taken together, these results suggest that CD25(+)CD4(+) and CD25(-)CD4(+) T cell sensitivity to Fas-dependent apoptosis is dynamically modulated during immune responses; this modulation appears to help maintain a permanent population of regulatory T cells required to control effector T cells.
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Affiliation(s)
- Alice Banz
- Institut National de la Santé et de la Recherche Médicale, Unité 345, Institut Necker, Paris, France
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105
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Abstract
Apoptosis or programmed cell death (PCD) is an active process of cellular self-destruction, essential for embryonic development and maintenance of homeostasis of multicellular organisms. Programmed cell death induction can serve as a defence mechanism of the host against intracellular microbes. Virus infections trigger host cell apoptosis, which can either limit virus production or contribute directly to viral pathogenesis. Several independent laboratories have identified "tissue" transglutaminase (tTG) as a potentially important player of the cell death program(s). This gene is specifically expressed in cells dying during mammalian development as well as in those undergoing apoptosis in various patho-physiological and experimental settings [Eur. J. Cell Biol. 56 (1991) 170; Piacentini, M., Davies, P.J.A., Fesus, L., 1994. Tissue transglutaminase in cells undergoing apoptosis. In: Tomei, L.D., Cope, F.O. (Eds.), Apoptosis II: The molecular basis of apoptosis in disease. Cold Spring Harbor Lab. Press, pp. 143-165.]. This chapter reviews recent studies concerning the expression and the possible role of "tissue" transglutaminase (tTG) in apoptotic cells; particular emphasis is given to its expression in the cell death pathways associated with HIV infection in the immune system. We propose here that the induction of the tTG gene in cells of the immune system, as well as the detection of the isodipeptide epsilon(gamma-glutamyl)lysine in plasma, are useful markers of apoptosis and might make it possible to monitor disease progression in HIV-infected individuals.
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106
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Reddy Avula CP, Lawrence RA, Zaman K, Fernandes G. Inhibition of intracellular peroxides and apoptosis of lymphocytes in lupus-prone B/W mice by dietary n-6 and n-3 lipids with calorie restriction. J Clin Immunol 2002; 22:206-19. [PMID: 12148595 DOI: 10.1023/a:1016088708457] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Our earlier studies have shown that calorie restriction and n-3 fatty acids inhibit autoimmune disease and prolong life span. Experiments were designed to study the alteration of apoptosis and its mediators in B/W mice fed either n-6 fatty acids [5% corn oil (CO)] or n-3 fatty acids [5% fish oil (FO)] and either allowed access to the diet ad libitum (AL) or restricted in caloric intake by 40% (CR), from 4 weeks of age. At 4 months (young) and 9 months (old) mice were killed, splenic lymphocytes were isolated, and apoptosis was measured with Annexin V and PI staining. Apoptosis was decreased in splenic lymphocytes from both young and old CR mice compared to their respective AL-fed control groups regardless of fat source. Increasing apoptosis with age was observed in CO/AL, CO/CR, and FO/AL mice which correlated closely with significantly higher cellular peroxides measured by flow cytometry using dichlorofluourescein diacetate (DCFH-DA), whereas in both CO/CR and FO/CR peroxide levels remained low in old mice. Furthermore, CR increased the proliferative response of splenic lymphocytes and decreased the Fas (CD95) and Fas-L protein expression in CD4+ lymphocytes from old mice. Higher levels of Fas and Fas-L expression were observed in old mice compared to young mice. Bcl-2 levels were elevated in both young and old CR groups compared to the respective AL groups. Calorie restriction prevented the loss of CD8 cells in old mice fed both the CO and the FO diet. In summary, CR resulted in decreased apoptosis accompanied by alterations in Fas, Fas-L, and Bcl-2 expression in old mice, increased life span, and delayed onset of kidney disease.
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MESH Headings
- Animals
- Apoptosis
- Caloric Restriction
- Corn Oil/administration & dosage
- Dietary Fats, Unsaturated/administration & dosage
- Fas Ligand Protein
- Fatty Acids, Omega-3/administration & dosage
- Fatty Acids, Omega-6
- Fatty Acids, Unsaturated/administration & dosage
- Female
- Fish Oils/administration & dosage
- Lupus Erythematosus, Systemic/immunology
- Lupus Erythematosus, Systemic/metabolism
- Lupus Erythematosus, Systemic/pathology
- Lupus Erythematosus, Systemic/prevention & control
- Lupus Nephritis/immunology
- Lupus Nephritis/metabolism
- Lupus Nephritis/pathology
- Lupus Nephritis/prevention & control
- Lymphocyte Activation
- Lymphocytes/metabolism
- Lymphocytes/pathology
- Membrane Glycoproteins/genetics
- Mice
- Mice, Inbred NZB
- Peroxides/metabolism
- Proto-Oncogene Proteins c-bcl-2/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- fas Receptor/genetics
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Affiliation(s)
- C P Reddy Avula
- University of Texas Health Science Center, Department of Medicine, San Antonio 78229-3900, USA
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107
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Figueredo Dos Santos C, Tilkin-Mariame AF, De Préval C, Lakhdar-Ghazal F. Influence of histidine beta81 of HLA-DR101 on peptide binding and presentation to T-cell receptor. Hum Immunol 2002; 63:459-66. [PMID: 12039521 DOI: 10.1016/s0198-8859(02)00394-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
HA(306-318) is an immunodominant peptide of the hemagglutinin of influenza virus that binds to most human leukocyte antigen (HLA-DR) alleles, while p18(73-85) is a HIV peptide characterized as a DR101 binding peptide. Our results demonstrate that crystal relaxation leads to the loss of a hydrogen bond between the beta81 histidine and the HA(306-318) peptide. This histidine is also involved in the binding of superantigens like SEA via a coordination of a zinc atom. To monitor the interaction of these peptides with this histidine of HLA-DR molecules, chemical modification, peptide binding on HLA-DR101 wild type and mutated molecules, and proliferation experiments were conducted, together with molecular simulation of HLA-DR/peptide molecular complexes. Our data suggest a different binding peptide pattern, depending of whether the peptide is HLA-DR101 allele specific or a shared one. Furthermore, tyrosine substitution at position beta81 does not affect either peptide binding or HA(306-318) clone-specific T-cell proliferation. On the contrary, the alanine substitution at position HLA-DR101 beta81 abrogated both peptide binding and T-cell proliferation. These results suggest that the histidine 81 on the DRbeta chain plays an important role in the HLA-DR peptide binding, more likely by polar interactions of the amino acid side chain ring with the peptide.
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108
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Strauss G, Osen W, Debatin KM. Induction of apoptosis and modulation of activation and effector function in T cells by immunosuppressive drugs. Clin Exp Immunol 2002; 128:255-66. [PMID: 11985515 PMCID: PMC1906394 DOI: 10.1046/j.1365-2249.2002.01777.x] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Immunosuppressive drugs (ISD) are used for the prevention and treatment of graft rejection, graft-versus-host-disease (GVHD) and autoimmune disorders. The precise mechanisms by which ISD interfere with T cell activation and effector function or delete antigen-specific T cells are defined only partially. We analysed commonly used ISD such as dexamethasone (DEX), mycophenolic acid (MPA), FK506, cyclosporin A (CsA), rapamycin (RAP), methotrexate (MTX) and cyclophosphamide (CP) for apoptosis-induction and modulation of activation and effector function in human peripheral T cells, cytotoxic T cell lines (CTL) and Jurkat T cells. Of all drugs tested only CP and MTX prevented antigen-specific proliferation of T cells and decreased cytotoxicity of alloantigen specific CTL lines by direct induction of apoptosis. MTX and CP also slightly increased activation-induced cell death (AICD) and CD95-sensitivity. In contrast, all other drugs tested did not induce T cell apoptosis, increase CD95-sensitivity or AICD. CsA and FK506 even prevented AICD by down-modulation of CD95L. DEX, MPA, CsA, FK506 and RAP inhibited activation of naive T cells, but were not able to block proliferation of activated T cells nor decrease cytotoxic capacity of CTL lines. These results show that ISD can be classified according to their action on apoptosis-induction and inhibition of proliferation and would favour a rational combination therapy to delete existing reactive T cells and prevent further T cell activation.
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Affiliation(s)
- G Strauss
- University Children's Hospital, Ulm, Germany
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109
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Chen L, Koyanagi M, Fukada K, Imanishi K, Yagi J, Kato H, Miyoshi-Akiyama T, Zhang R, Miwa K, Uchiyama T. Continuous exposure of mice to superantigenic toxins induces a high-level protracted expansion and an immunological memory in the toxin-reactive CD4+ T cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:3817-24. [PMID: 11937534 DOI: 10.4049/jimmunol.168.8.3817] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We analyzed the responses of several T cell fractions reactive with superantigenic toxins (SAGTs), staphylococcal enterotoxin A (SEA), or Yersinia pseudotuberculosis-derived mitogen (YPM) in mice implanted with mini-osmotic pumps filled with SEA or YPM. In mice implanted with the SEA pump, SEA-reactive Vbeta3(+)CD4(+) T cells exhibited a high-level protracted expansion for 30 days, and SEA-reactive Vbeta11(+)CD4(+) T cells exhibited a low-level protracted expansion. SEA-reactive CD8(+) counterparts exhibited only a transient expansion. A similar difference in T cell expansion was also observed in YPM-reactive T cell fractions in mice implanted with the YPM pump. Vbeta3(+)CD4(+) and Vbeta11(+)CD4(+) T cells from mice implanted with the SEA pump exhibited cell divisions upon in vitro restimulation with SEA and expressed surface phenotypes as memory T cells. CD4(+) T cells from mice implanted with the SEA pump exhibited high IL-4 production upon in vitro restimulation with SEA, which was due to the enhanced capacity of the SEA-reactive CD4(+) T cells to produce IL-4. The findings in the present study indicate that, in mice implanted with a specific SAGT, the level of expansion of the SAGT-reactive CD4(+) T cell fractions varies widely depending on the TCR Vbeta elements expressed and that the reactive CD4(+) T cells acquire a capacity to raise a memory response. CD8(+) T cells are low responders to SAGTs.
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Affiliation(s)
- Luqiu Chen
- Department of Microbiology and Immunology, School of Medicine, Tokyo Women's Medical University, Ohtsu, Japan
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110
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Yarwood JM, McCormick JK, Paustian ML, Orwin PM, Kapur V, Schlievert PM. Characterization and expression analysis of Staphylococcus aureus pathogenicity island 3. Implications for the evolution of staphylococcal pathogenicity islands. J Biol Chem 2002; 277:13138-47. [PMID: 11821418 DOI: 10.1074/jbc.m111661200] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
We describe the complete sequence of the 15.9-kb staphylococcal pathogenicity island 3 encoding staphylococcal enterotoxin serotypes B, K, and Q. The island, which meets the generally accepted definition of pathogenicity islands, contains 24 open reading frames potentially encoding proteins of more than 50 amino acids, including an apparently functional integrase. The element is bordered by two 17-bp direct repeats identical to those found flanking staphylococcal pathogenicity island 1. The island has extensive regions of homology to previously described pathogenicity islands, particularly staphylococcal pathogenicity islands 1 and bov. The expression of 22 of the 24 open reading frames contained on staphylococcal pathogenicity island 3 was detected either in vitro during growth in a laboratory medium or serum or in vivo in a rabbit model of toxic shock syndrome using DNA microarrays. The effect of oxygen tension on staphylococcal pathogenicity island 3 gene expression was also examined. By comparison with the known staphylococcal pathogenicity islands in the context of gene expression described here, we propose a model of pathogenicity island origin and evolution involving specialized transduction events and addition, deletion, or recombination of pathogenicity island "modules."
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Affiliation(s)
- Jeremy M Yarwood
- Department of Microbiology, University of Minnesota Medical School, 420 Delaware Street SE, Minneapolis, MN 55455, USA
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111
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Nishimura M, Fujiyama Y, Niwakawa M, Sasaki T, Bamba T. In vivo cytokine responses in gut-associated lymphoid tissue (GALT) and spleen following oral administration of staphylococcal enterotoxin B. Immunol Lett 2002; 81:77-85. [PMID: 11841849 DOI: 10.1016/s0165-2478(01)00334-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The mechanisms responsible for oral tolerance have been analyzed using various antigens. The induction of oral nonresponsiveness to low doses of Staphylococcal Enterotoxin B (SEB), in which SEB-reactive clonal anergy and deletion are involved, has also been confirmed. However, few reports have examined the cytokine milieu of the mucosal and peripheral lymphoid tissue during tolerance induction after the oral administration of SEB. In this study, to elucidate the mechanism responsible for the oral tolerance to low dose of SEB, the cytokine responses of the gut-associated lymphoid tissues (GALT) and the spleen were examined using the reverse transcription-polymerase chain reaction (RT-PCR) method. After the oral administration of a single low dose of SEB, the expressions of Th2 and TGF-beta, and to a lesser extent Th1 mRNA were observed in the mucosa. In contrast, following repeated oral low doses of SEB, in a manner different from previous results using conventional antigens, no cytokine enhancements were demonstrated in the GALT or the spleen. In conclusion, the involvement of unknown inhibitory or regulatory cytokines, together with SEB-reactive clonal anergy and deletion, is suggested in the induction of oral tolerance to low dose SEB.
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Affiliation(s)
- Masako Nishimura
- Department of Internal Medicine, Shiga University of Medical Science, Tsukinowa-cho, Seta, Otsu, Shiga 520-2192, Japan.
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112
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Huang CY, Golub R, Wu GE, Kanagawa O. Superantigen-induced TCR alpha locus secondary rearrangement: role in tolerance induction. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:3259-65. [PMID: 11907080 DOI: 10.4049/jimmunol.168.7.3259] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Immunization with superantigen in vivo induces transient activation of superantigen-specific T cells, followed by a superantigen-nonresponsive state. In this study, using a TCR alpha knock-in mouse in which the knock-in alpha-chain can be replaced with endogenous alpha-chain through secondary rearrangement, we show that immunization of superantigen changes the TCR alpha-chain expression on peripheral superantigen-specific T cells, induces expression of recombination-activating genes, and generates DNA double-strand breaks at the TCR alpha-chain locus. These results suggest that viral superantigens are capable of inducing peripheral TCR revision. Our findings thus provide a new perspective on pathogen-immune system interaction.
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MESH Headings
- Animals
- Antigens/pharmacology
- Cell Differentiation/genetics
- Cell Differentiation/immunology
- Columbidae
- Cytochrome c Group/immunology
- Cytochrome c Group/pharmacology
- Down-Regulation/genetics
- Down-Regulation/immunology
- Gene Rearrangement, alpha-Chain T-Cell Antigen Receptor/immunology
- Genes, T-Cell Receptor alpha/immunology
- Immune Tolerance/genetics
- Immunization
- Injections, Intravenous
- Lymphocyte Activation/genetics
- Mice
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Mice, Knockout
- Mice, Transgenic
- Receptors, Antigen, T-Cell, alpha-beta/antagonists & inhibitors
- Receptors, Antigen, T-Cell, alpha-beta/biosynthesis
- Receptors, Antigen, T-Cell, alpha-beta/genetics
- Spleen/cytology
- Spleen/immunology
- Superantigens/administration & dosage
- Superantigens/immunology
- Superantigens/pharmacology
- T-Lymphocytes/cytology
- T-Lymphocytes/immunology
- T-Lymphocytes/metabolism
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Affiliation(s)
- Ching-Yu Huang
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA
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113
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Llewelyn M, Cohen J. Superantigens: microbial agents that corrupt immunity. THE LANCET. INFECTIOUS DISEASES 2002; 2:156-62. [PMID: 11944185 DOI: 10.1016/s1473-3099(02)00222-0] [Citation(s) in RCA: 200] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Microbial superantigens are a family of protein exotoxins that share the ability to trigger excessive and aberrant activation of T cells. The best characterised are the staphylococcal enterotoxins and the streptococcal pyrogenic exotoxins that trigger the staphylococcal and streptococcal toxic shock syndromes. It is now apparent that superantigens have a wider role in the pathology of infectious diseases than has previously been appreciated. Staphylococcus aureus and Streptococcus pyogenes together produce 19 different superantigens. The range of microorganisms known to produce superantigens has expanded to include Gram negative bacteria, mycoplasma, and viruses. Research is beginning to shed light on the more subtle parts these molecules play in causing disease and to produce some real possibilities for specific treatment of superantigen-induced toxicity. We aim to highlight these new developments and review the science behind these fascinating molecules.
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Affiliation(s)
- Martin Llewelyn
- Department of Infectious Diseases, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK.
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114
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Soos JM, Mujtaba MG, Schiffenbauer J, Torres BA, Johnson HM. Intramolecular epitope spreading induced by staphylococcal enterotoxin superantigen reactivation of experimental allergic encephalomyelitis. J Neuroimmunol 2002; 123:30-4. [PMID: 11880146 DOI: 10.1016/s0165-5728(01)00476-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The staphylococcal enterotoxin superantigens are among the most potent T cell stimulators known. They have been shown to alter the course of disease in experimental allergic encephalomyelitis, an animal model for multiple sclerosis (MS). We have previously demonstrated that two of the staphylococcal enterotoxins, SEA and SEB, are able to reactivate paralysis in PL/J mice which had been immunized with myelin basic protein (MBP) and resolved an initial episode of paralysis. In PL/J mice, Ac1-11 is the dominant encephalitogenic determinant of MBP. We hypothesized that superantigen reactivation of experimental allergic encephalomyelitis (EAE) may result in the spreading of T cell specificities for other epitopes of MBP. PL/J mice which had resolved an initial episode of EAE were treated with SEA and developed a second episode of paralysis. At the onset of symptoms, mice were sacrificed and splenocytes were stimulated in vitro with a panel of MBP peptides. EAE reactivation by SEA resulted in the spreading of T cell specificites to residues 100 to 120 of MBP. While intramolecular spreading did occur, spreading to other antigens did not, as evidenced by the lack of response to a proteolipid protein (PLP) peptide and heat shock protein 60 (hsp 60). To further characterize the epitope MBP 100-120, PL/J mice were immunized with MBP 100-120. No initial development of disease was observed. However, administration of SEA 2 weeks after MBP 100-120 immunization resulted in the onset of paralysis. In addition to a proliferative response to MBP 100-120, these mice also exhibited a proliferative response to the flanking MBP peptides 81-100 and 120-140. Thus, SEA is able to induce intramolecular epitope spreading in PL/J mice after reactivation of EAE.
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Affiliation(s)
- Jeanne M Soos
- Department of Microbiology and Cell Science, Box 110700, University of Florida, Gainesville, FL 32611, USA
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115
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Zhang Y, Schlossman SF, Edwards RA, Ou CN, Gu J, Wu MX. Impaired apoptosis, extended duration of immune responses, and a lupus-like autoimmune disease in IEX-1-transgenic mice. Proc Natl Acad Sci U S A 2002; 99:878-83. [PMID: 11782530 PMCID: PMC117399 DOI: 10.1073/pnas.022326699] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Susceptibility of activated T cells to apoptosis must be tightly regulated to ensure sufficient T cell progeny for an effective response, while allowing a rapid depletion of them at the end of the immune response. We show here that a previously isolated, NF-kappa B/rel target gene IEX-1 (Immediate Early response gene X-1) is highly expressed in T cells at early stages of activation, but declines with a prolonged period of activation time, coincident with an increased susceptibility of T cells to apoptosis during the late phases of an immune response. Transgenic expression of IEX-1 specifically in lymphocytes impaired apoptosis in activated T cells, extended a duration of an effector-phase of a specific immune response, and increased the accumulation of effector/memory-like T cells and the susceptibility to a lupus-like autoimmune disease. Our study demonstrated an antiapoptotic effect of IEX-1 on T cell apoptosis triggered by ligation of Fas and T cell receptor (TCR)/CD3 complex. The ability of extending life expectancy of T effectors, in line with a decrease in its expression following prolonged T cell activation, suggests a key role for IEX-1 in regulating T cell homeostasis during immune responses.
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Affiliation(s)
- Y Zhang
- Department of Pathology, Baylor College of Medicine, Houston, TX 77030, USA
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116
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McCormick JK, Yarwood JM, Schlievert PM. Toxic shock syndrome and bacterial superantigens: an update. Annu Rev Microbiol 2002; 55:77-104. [PMID: 11544350 DOI: 10.1146/annurev.micro.55.1.77] [Citation(s) in RCA: 480] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Toxic shock syndrome (TSS) is an acute onset illness characterized by fever, rash formation, and hypotension that can lead to multiple organ failure and lethal shock, as well as desquamation in patients that recover. The disease is caused by bacterial superantigens (SAGs) secreted from Staphylococcus aureus and group A streptococci. SAGs bypass normal antigen presentation by binding to class II major histocompatibility complex molecules on antigen-presenting cells and to specific variable regions on the beta-chain of the T-cell antigen receptor. Through this interaction, SAGs activate T cells at orders of magnitude above antigen-specific activation, resulting in massive cytokine release that is believed to be responsible for the most severe features of TSS. This review focuses on clinical and epidemiological aspects of TSS, as well as important developments in the genetics, biochemistry, immunology, and structural biology of SAGs. From the evolutionary relationships between these important toxins, we propose that there are five distinct groups of SAGs.
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Affiliation(s)
- J K McCormick
- Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
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117
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Kominsky SL, Torres BA, Hobeika AC, Lake FA, Johnson HM. Superantigen enhanced protection against a weak tumor-specific melanoma antigen: implications for prophylactic vaccination against cancer. Int J Cancer 2001; 94:834-41. [PMID: 11745486 DOI: 10.1002/ijc.1551] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
B16F10 melanoma is a tumor derived from C57BL/6 mice that has been found to be poorly immunogenic and highly aggressive. Here we have shown that vaccination of mice with irradiated B16F10 cells followed by treatment with a combination of staphylococcal enterotoxins A and B (SEA/SEB) leads to significant and specific protection against subsequent challenge with viable B16F10 cells (at least 25-fold greater than a lethal dose). Also, 75% of mice surviving over 150 days remained tumor-free after rechallenge with viable B16F10 cells, evidence of the development of strong immunologic memory. Additional studies showed increases in CD4(+) and CD8(+) T-cell populations, cytotoxic T-lymphocyte activity and interferon-gamma production, all of which may contribute to enhanced survival. Furthermore, failure to produce protection in either CD4(-/-) or CD8(-/-) T-cell knockout mice is evidence that CD4(+) and CD8(+) T cells play an essential role in induction of immunity. These results show that superantigen administration subsequent to vaccination with inactivated tumor cells results in protective antitumor immunity. Thus, prophylactic vaccination against cancer is a feasible method for arming the immune system prior to the incidence of cancer.
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Affiliation(s)
- S L Kominsky
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
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118
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Bleesing JJ, Morrow MR, Uzel G, Fleisher TA. Human T cell activation induces the expression of a novel CD45 isoform that is analogous to murine B220 and is associated with altered O-glycan synthesis and onset of apoptosis. Cell Immunol 2001; 213:72-81. [PMID: 11747358 DOI: 10.1006/cimm.2001.1865] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activated T cells undergo changes during their transition to T cell blasts and, subsequently, via a phase of anergy, to apoptosis. For example, activated murine T cell blasts express the B-cell-specific CD45R isoform, B220, a marker also present on T cells in mice and humans with defective Fas-mediated apoptosis in vivo, suggesting a role for B220 up-regulation in the transition of activation to apoptosis. Human T cells, activated in vitro with superantigens and mitogens, also express B220 as they undergo blastogenesis and cell cycle progression. B220 expression peaks on T cells undergoing apoptosis. CD43-hexasaccharide glycoform expression and lectin binding profiles indicate that B220 expression is reflective of altered O-linked glycan biosynthesis found in specific T cell subsets transitioning through the phases of proliferation, anergy, and apoptosis. Potential implications of these alterations include changes in lymphocyte adhesion and trafficking and homeostasis through altered sensitivity to Fas-dependent and independent pathways of apoptosis.
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Affiliation(s)
- J J Bleesing
- Department of Laboratory Medicine, National Institutes of Health, Bethesda, Maryland 20892, USA.
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119
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Abstract
Apoptosis or programmed cell death is an essential physiological process that plays a critical role in development and tissue homeostasis. However, apoptosis is also involved in a wide range of pathological conditions. Apoptotic cells may be characterized by specific morphological and biochemical changes, including cell shrinkage, chromatin condensation, and internucleosomal cleavage of genomic DNA. At the molecular level, apoptosis is tightly regulated and is mainly orchestrated by the activation of the aspartate-specific cysteine protease (caspase) cascade. There are two main pathways leading to the activation of caspases. The first of these depends upon the participation of mitochondria (receptor-independent) and the second involves the interaction of a death receptor with its ligand. Pro- and anti-apoptotic members of the Bcl-2 family regulate the mitochondrial pathway. Cellular stress induces pro-apoptotic Bcl-2 family members to translocate from the cytosol to the mitochondria, where they induce the release of cytochrome c, while the anti-apoptotic Bcl-2 proteins work to prevent cytochrome c release from mitochondria, and thereby preserve cell survival. Once in the cytoplasm, cytochrome c catalyzes the oligomerization of apoptotic protease activating factor-1, thereby promoting the activation of procaspase-9, which then activates procaspase-3. Alternatively, ligation of death receptors, like the tumor necrosis factor receptor-1 and the Fas receptor, causes the activation of procaspase-8. The mature caspase may now either directly activate procaspase-3 or cleave the pro-apoptotic Bcl-2 homology 3-only protein Bid, which then subsequently induces cytochrome c release. Nevertheless, the end result of either pathway is caspase activation and the cleavage of specific cellular substrates, resulting in the morphological and biochemical changes associated with the apoptotic phenotype.
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Affiliation(s)
- K C Zimmermann
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, 10355 Science Center Drive, San Diego, CA 92121, USA.
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120
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Tsitsikov EN, Laouini D, Dunn IF, Sannikova TY, Davidson L, Alt FW, Geha RS. TRAF1 is a negative regulator of TNF signaling. enhanced TNF signaling in TRAF1-deficient mice. Immunity 2001; 15:647-57. [PMID: 11672546 DOI: 10.1016/s1074-7613(01)00207-2] [Citation(s) in RCA: 149] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
TNF receptor-associated factor 1 (TRAF1) is a unique TRAF protein because it lacks a RING finger domain and is predominantly expressed in activated lymphocytes. To elucidate the function of TRAF1, we generated TRAF1-deficient mice. TRAF1(-/-) mice are viable and have normal lymphocyte development. TRAF1(-/-) T cells exhibit stronger than wild-type (WT) T cell proliferation to anti-CD3 mAb, which persisted in the presence of IL-2 or anti-CD28 antibodies. Activated TRAF1(-/-) T cells, but not TRAF1(+/+) T cells, responded to TNF by proliferation and activation of the NF-kappa B and AP-1 signaling pathways. This TNF effect was mediated by TNFR2 (p75) but not by TNFR1 (p55). Furthermore, skin from TRAF1(-/-) mice was hypersensitive to TNF-induced necrosis. These findings suggest that TRAF1 is a negative regulator of TNF signaling.
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Affiliation(s)
- E N Tsitsikov
- Division of Immunology, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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121
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Stohl W, Xu D, Zang S, Kim KS, Li L, Hanson JA, Stohlman SA, David CS, Jacob CO. In vivo staphylococcal superantigen-driven polyclonal Ig responses in mice: dependence upon CD4(+) cells and human MHC class II. Int Immunol 2001; 13:1291-300. [PMID: 11581174 DOI: 10.1093/intimm/13.10.1291] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Staphylococcal enterotoxin (SE) B and seven other staphylococcal superantigens (SAg), despite promoting vigorous Ig production in human peripheral blood mononuclear cell cultures, are exceedingly poor at eliciting Ig responses in cultures of spleen cells from C57BL/10J (B10) or C3H/HeJ mice. In contrast, SEB elicits Ig responses in cultures of spleen cells from human MHC class II-transgenic mice. Whereas i.p. administration of SEB (0.2-20 microg) to non-transgenic B10 mice elicits very weak in vivo Ig responses, identical treatment of CD4(+) cell-intact (but not CD4(+) cell-depleted) human MHC class II-transgenic mice elicits dramatic increases in both splenic Ig-secreting cells and serum Ig levels. Over a 2-week period, the SEB-induced in vivo Ig responses peak and then plateau or fall in association with a preferential increase in splenic CD8(+) cells. Nevertheless, in vivo depletion of CD8(+) cells has no sustained effect on SEB-driven Ig responses. Taken together, these observations demonstrate that the effects of SAg on in vivo humoral immune responses are highly CD4(+) cell dependent, are substantially CD8(+) cell independent and can be successfully investigated using human MHC class II-transgenic mice. This model system may be useful in investigating the polyclonally activating effects of microbial products (prototypic environmental insults) on the development of systemic autoimmunity.
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Affiliation(s)
- W Stohl
- Division of Rheumatology and Immunology, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, HMR 711, Los Angeles, CA 90033, USA
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122
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Wells AD, Li XC, Strom TB, Turka LA. The role of peripheral T-cell deletion in transplantation tolerance. Philos Trans R Soc Lond B Biol Sci 2001; 356:617-23. [PMID: 11375065 PMCID: PMC1088449 DOI: 10.1098/rstb.2001.0845] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The apoptotic deletion of thymocytes that express self-reactive antigen receptors is the basis of central (thymic) self-tolerance. However, it is clear that some autoreactive T cells escape deletion in the thymus and exist as mature lymphocytes in the periphery. Therefore, peripheral mechanisms of tolerance are also crucial, and failure of these peripheral mechanisms leads to autoimmunity. Clonal deletion, clonal anergy and immunoregulation and/or suppression have been suggested as mechanisms by which 'inappropriate' T-lymphocyte responses may be controlled in the periphery. Peripheral clonal deletion, which involves the apoptotic elimination of lymphocytes, is critical for T-cell homeostasis during normal immune responses, and is recognized as an important process by which self-tolerance is maintained. Transplantation of foreign tissue into an adult host represents a special case of 'inappropriate' T-cell reactivity that is subject to the same central and peripheral tolerance mechanisms that control reactivity against self. In this case, the unusually high frequency of naive T cells able to recognize and respond against non-self-allogeneic major histocompatibility complex (MHC) antigens leads to an exceptionally large pool of pathogenic effector lymphocytes that must be controlled if graft rejection is to be avoided. A great deal of effort has been directed toward understanding the role of clonal anergy and/or active immunoregulation in the induction of peripheral transplantation tolerance but, until recently, relatively little progress had been made towards defining the potential contribution of clonal deletion. Here, we outline recent data that define a clear requirement for deletion in the induction of peripheral transplantation tolerance across MHC barriers, and discuss the potential implications of these results in the context of current treatment modalities used in the clinical transplantation setting.
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Affiliation(s)
- A D Wells
- Department of Medicine, University of Pennsylvania, 415 Curie Boulevard, Philadelphia, PA 19104, USA
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123
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Abstract
T-cell differentiation in the thymus generates a peripheral repertoire of mature T cells that mounts strong responses to foreign antigens but is largely unresponsive to self-antigens. This state of specific immunological tolerance to self-components involves both central and peripheral mechanisms. Here we review the process whereby many T cells with potential reactivity for self-antigens are eliminated in the thymus during early T-cell differentiation. This process of central tolerance (negative selection) reflects apoptosis and is a consequence of immature T cells receiving strong intracellular signalling through T-cell receptor (TCR) recognition of peptides bound to major histocompatibility complex (MHC) molecules. Central tolerance occurs mainly in the medullary region of the thymus and depends upon contact with peptide-MHC complexes expressed on bone-marrow-derived antigen-presenting cells (APCs); whether tolerance also occurs in the cortex is still controversial. Tolerance induction requires a combination of TCR ligation and co-stimulatory signals. Co-stimulation reflects interaction between complementary molecules on T cells and APCs and probably involves multiple molecules acting in consort, which may account for why deletion of individual molecules with known or potential co-stimulatory function has little or no effect on central tolerance. The range of self-antigens that induce central tolerance is considerable and, via low-level expression in the thymus, may also include tissue-specific antigens; central tolerance to these latter antigens, however, is likely to be limited to high-affinity T cells, leaving low-affinity cells to escape. Tolerance to alloantigens and the possibility of using central tolerance to promote acceptance of allografts are discussed.
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Affiliation(s)
- J Sprent
- Department of Immunology, IMM4, The Scripps Research Institute, 10550 North Torrey Pines Road, LaJolla, CA 92037, USA.
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124
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Hsu LJ, Lin YS. Roles of I-E molecule and CD28 costimulation in induction of suppression by staphylococcal enterotoxin B in vivo. Cell Immunol 2001; 212:35-43. [PMID: 11716527 DOI: 10.1006/cimm.2001.1841] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exposure to bacterial superantigens leads to the induction of a subsequent state of immune hyporesponsiveness. Using a transwell coculture system, a previous report demonstrated that splenocytes from staphylococcal enterotoxin B (SEB)-injected BALB/c mice secreted soluble mediators to suppress the proliferative response of naive syngeneic splenocytes to SEB stimulation. We show in the present study that, in contrast to the suppressive effect induced by SEB in BALB/c (H-2(d) haplotype), MRL(+/+), and MRL-lpr/lpr (H-2(k)) mice, SEB-primed splenocytes from I-E(-) strains such as B6, B10, A. BY (H-2(b)), and A.SW (H-2(s)) mice failed to inhibit the CD25 expression and the proliferative activity of their syngeneic naive responder splenocytes. Further results revealed that the SEB-primed cells from BALB/c, but not B6, mice inhibited the CD25 expression and proliferation of naive responder cells from either BALB/c or B6 mice, indicating the critical regulatory role of the effector cells. Unlike SEB, staphylococcal enterotoxin A induced profound suppression in both BALB/c and B6 mice. Moreover, the suppressive competence of SEB-primed splenocytes was diminished in CD28-deficient BALB/c mice. Taken together, our results indicate that when SEB is used as a stimulator in vivo, both the I-E molecule and CD28 costimulation are required for the induction of regulatory cells bearing suppressive activity.
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Affiliation(s)
- L J Hsu
- Department of Microbiology and Immunology, National Cheng Kung University Medical College, Tainan, Taiwan, Republic of China
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125
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Tanchot C, Barber DL, Chiodetti L, Schwartz RH. Adaptive tolerance of CD4+ T cells in vivo: multiple thresholds in response to a constant level of antigen presentation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 167:2030-9. [PMID: 11489985 DOI: 10.4049/jimmunol.167.4.2030] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The in vivo T cell response to persistent Ag contains a hyporesponsive phase following an initial expansion and subsequent partial deletion of the responding cells. The mechanism(s) responsible for this tolerance process is poorly understood. In this study, we describe a new paired transgenic model (TCR and Ag), which within 7-14 days produces 20-40 million hyporesponsive T cells. This state is characterized by an 85-95% reduction in all cytokine production, an impairment of re-expression of CD25 and CD69, and a desensitization of the proliferative response to Ag. TCR levels were normal, and in vivo mixing experiments showed no evidence for active suppression. The hyporesponsiveness partially dissipated without proliferation when the cells were transferred into a non-Ag-bearing host. If the second host expressed Ag, the T cells initially regained responsiveness, but then slowly entered an even deeper state of tolerance characterized by an additional 7- to 10-fold lowering of cytokine production and a greater desensitization of proliferation. Surprisingly, this readaptation took place with the same level of Ag presentation, suggesting that other parameters can influence the tolerance threshold. Both the readjustment in sensitivity and the reversal without Ag convincingly demonstrate for the first time a truly adaptive tolerance process in CD4+ T cells in vivo.
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MESH Headings
- Adaptation, Physiological/genetics
- Adaptation, Physiological/immunology
- Adoptive Transfer/methods
- Animals
- Antigen Presentation/genetics
- Antigen-Presenting Cells/immunology
- CD3 Complex/biosynthesis
- CD3 Complex/genetics
- CD4-Positive T-Lymphocytes/immunology
- CD4-Positive T-Lymphocytes/transplantation
- Columbidae
- Cytochrome c Group/genetics
- Cytochrome c Group/immunology
- Dose-Response Relationship, Immunologic
- Immune Tolerance/genetics
- Interphase/genetics
- Interphase/immunology
- Lymphocyte Activation/genetics
- Mice
- Mice, Inbred A
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Receptors, Antigen, T-Cell, alpha-beta/genetics
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Affiliation(s)
- C Tanchot
- Laboratory of Cellular and Molecular Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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126
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Abstract
Although short- and long-term results after organ transplantation have improved considerably in recent years, morbidity and mortality rates in graft recipients remain high. The induction of lifelong donor-specific tolerance would dramatically improve outcome after organ transplantation. Although many tolerance protocols have been successful in rodent studies, most of these approaches have failed when attempted in large animals or humans. Robust tolerance, in contrast, has been demonstrated with mixed chimerism regimens not only in rodents but also in large animal models, including non-human primates. Furthermore, mixed chimerism protocols have been developed that would be feasible in cadaveric, and thus in thoracic, transplantation. The induction of mixed hematopoietic chimerism is therefore an attractive experimental approach for development of clinical tolerance protocols. One of the obstacles to widespread clinical application of this concept is the remaining toxicity of the host conditioning. Recent advances, however, have led to substantially milder protocols that could become clinically acceptable in the foreseeable future. This article provides a short overview of the basic mechanisms by which immunologic tolerance may be induced, describes the concept of mixed chimerism as a promising approach for clinical tolerance induction, and reviews recent progress in developing clinically feasible mixed chimerism protocols.
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Affiliation(s)
- T Wekerle
- Division of Transplantation, Department of Surgery, Vienna General Hospital, University of Vienna, Vienna, Austria.
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127
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Suzuki A, Yamaguchi MT, Ohteki T, Sasaki T, Kaisho T, Kimura Y, Yoshida R, Wakeham A, Higuchi T, Fukumoto M, Tsubata T, Ohashi PS, Koyasu S, Penninger JM, Nakano T, Mak TW. T cell-specific loss of Pten leads to defects in central and peripheral tolerance. Immunity 2001; 14:523-34. [PMID: 11371355 DOI: 10.1016/s1074-7613(01)00134-0] [Citation(s) in RCA: 413] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
PTEN, a tumor suppressor gene, is essential for embryogenesis. We used the Cre-loxP system to generate a T cell-specific deletion of the Pten gene (Pten(flox/-) mice). All Pten(flox/-) mice develop CD4+ T cell lymphomas by 17 weeks. Pten(flox/-) mice show increased thymic cellularity due in part to a defect in thymic negative selection. Pten(flox/-) mice exhibit elevated levels of B cells and CD4+ T cells in the periphery, spontaneous activation of CD4+ T cells, autoantibody production, and hypergammaglobulinemia. Pten(flox/-) T cells hyperproliferate, are autoreactive, secrete increased levels of Th1/Th2 cytokines, resist apoptosis, and show increased phosphorylation of PKB/Akt and ERK. Peripheral tolerance to SEB is also impaired in Pten(flox/-) mice. PTEN is thus an important regulator of T cell homeostasis and self-tolerance.
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MESH Headings
- Animals
- Apoptosis/immunology
- CD4-Positive T-Lymphocytes/cytology
- CD4-Positive T-Lymphocytes/immunology
- Cell Division
- Cytokines/biosynthesis
- DNA-Binding Proteins/metabolism
- Enterotoxins/immunology
- Female
- Genes, Tumor Suppressor
- I-kappa B Proteins
- Immune Tolerance
- Lymphatic Diseases/immunology
- Lymphoma, T-Cell/immunology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Mitogen-Activated Protein Kinases/metabolism
- PTEN Phosphohydrolase
- Phosphoric Monoester Hydrolases/genetics
- Phosphoric Monoester Hydrolases/immunology
- Protein Serine-Threonine Kinases
- Proto-Oncogene Proteins/metabolism
- Proto-Oncogene Proteins c-akt
- Proto-Oncogene Proteins c-bcl-2/metabolism
- Receptors, Antigen/genetics
- Receptors, Antigen/immunology
- Receptors, Antigen, T-Cell/genetics
- Receptors, Antigen, T-Cell/immunology
- Splenomegaly
- Staphylococcus aureus/immunology
- Superantigens/immunology
- Thymus Gland/abnormalities
- Thymus Gland/cytology
- Tumor Suppressor Proteins
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Affiliation(s)
- A Suzuki
- Department of Molecular and Cellular Biology, Osaka University, 565-0871, Osaka, Japan
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128
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Pahlavani MA, Mele JF, Richardson A. Effect of overexpression of human Cu/Zn-SOD on activation-induced lymphocyte proliferation and apoptosis. Free Radic Biol Med 2001; 30:1319-27. [PMID: 11368930 DOI: 10.1016/s0891-5849(01)00529-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The process of lymphocyte proliferation and apoptosis is known to be linked to oxidative stress. In the present study, we have used a new transgenic mouse model to investigate the effect of human Cu/Zn superoxide dismutase (Cu/Zn-SOD) overexpression on activation-induced lymphocytes proliferation and apoptosis. Cu/Zn-SOD activity was 3.5-fold higher in the spleen of the transgenic mice overexpressing Cu/Zn-SOD (Tg-Cu/Zn-SOD) compared to the wild-type littermates. Proliferative response of lymphocytes to lipopolysaccharide (LPS), Concanavalin A (Con A), and anti-CD3 was measured by [3H]-thymidine incorporation. Activation-induced apoptosis was determined by incubating the T cells with anti-CD3 (primary stimulus) for 72 h, followed by restimulation with Con A (secondary stimulus) for various times. Apoptosis was assessed by measuring DNA fragmentation using a spectrofluorimetric assay and monitoring the expression of the specific apoptotic markers (Fas/CD95 receptor and Fas/CD95 ligand (Fas-L) using flow cytometry. There was no significant difference in proliferative response of lymphocytes to LPS, Con A, or anti-CD3 in transgenic mice overexpressing human Cu/Zn superoxide dismutase (Tg-Cu/Zn-SOD) compared to wild-type littermates. In addition, no significant difference was observed in lymphocyte populations and subsets between Tg-Cu/Zn-SOD mice and wild-type littermates. However, splenic T cells from Tg-Cu/Zn-SOD mice exhibited a significantly (p <.05) higher level of activation-induced DNA fragmentation than T cells from wild-type littermates. The increase in DNA fragmentation was paralleled with an increase in the proportion of T cells expressing Fas and Fas-L molecules. The possible consequences of Cu/Zn-SOD overproduction on activation-induced apoptosis are discussed.
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Affiliation(s)
- M A Pahlavani
- South Texas Veterans Health Care System, Audie L. Murphy Veterans Hospital, and Department of Physiology, University of Texas Health Science Center, San Antonio, TX 78284, USA.
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129
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Affiliation(s)
- K Migita
- First Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki, Japan.
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130
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Mitchell TC, Hildeman D, Kedl RM, Teague TK, Schaefer BC, White J, Zhu Y, Kappler J, Marrack P. Immunological adjuvants promote activated T cell survival via induction of Bcl-3. Nat Immunol 2001; 2:397-402. [PMID: 11323692 DOI: 10.1038/87692] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Injection of soluble protein antigen into animals causes abortive proliferation of the responding T cells. Immunological adjuvants boost T cell responses at least in part by increasing the survival of activated T cells during and after the initial proliferative phase of their clonal expansion. To understand how adjuvants promote T cell survival, we used gene microarrays to analyze gene expression in T cells activated either with antigen alone or in the presence of two different adjuvants. Among the genes whose expression was increased by both adjuvants was the IkappaB family member Bcl-3. Retroviral infection experiments showed that expression of Bcl-3 increased survival of activated T cells in vitro and in vivo. Adjuvants may therefore improve survival of activated T cells via induction of Bcl-3.
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Affiliation(s)
- T C Mitchell
- Howard Hughes Medical Institute, University of Colorado Health Sciences Center, Denver, CO 80206, USA
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131
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Noël C, Florquin S, Goldman M, Braun MY. Chronic exposure to superantigen induces regulatory CD4(+) T cells with IL-10-mediated suppressive activity. Int Immunol 2001; 13:431-9. [PMID: 11282982 DOI: 10.1093/intimm/13.4.431] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The repeated injection of bacterial superantigens (SAg), such as staphylococcus enterotoxin (SE) A or B, has been shown in mice to induce a state of unresponsiveness characterized by the lack of secretion of Th1 lymphokines, such as IL-2 and IFN-gamma, following subsequent SAg challenge. We made the observation, in vivo as well as in vitro, that unresponsiveness to SAg could be transferred from SEA- to SEB-reactive T cells (and reversibly from SEB- to SEA-specific T cells) in C57BL/6 mice but not in BALB/c mice. Since C57BL/6 mice, unlike BALB/c mice, possess TCR V(beta)3+ and V(beta)11+ T cells able to react with both SEA and SEB, we hypothesized that SAg-unresponsive V(beta)3(+) and V(beta)11+ T cells could mediate linked suppression of other SAg-reactive T cells. To analyze further this possibility, spleen cells from BALB/c mice made unresponsive to SEB were tested for their capacity to suppress the response of normal BALB/c cells to SEB. The production of both IFN-gamma and IL-2 following SEB stimulation was greatly impaired in co-cultures containing CD4(+) T cells, but not CD8(+) T cells, isolated from unresponsive animals. In vivo, the production of both IFN-gamma and IL-2 responses to SEB was dramatically reduced in animals adoptively transferred with unresponsive spleen cells. This suppression was abrogated in recipients injected with neutralizing anti-IL-10 antibodies. Moreover, in animals made unresponsive to SEB, SAg-reactive CD4(+) T cells were found to express high levels of CTLA-4, a molecule recently described to play an essential role in the suppressive function of regulatory T cells. Taken together these results demonstrate that the repetitive injection of SAg induces the differentiation of regulatory CD4(+) T cells capable of suppressing SAg-reactive naive T cells.
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Affiliation(s)
- C Noël
- Laboratory of Experimental Immunology, Université Libre de Bruxelles, 808 route de Lennik, 1070 Brussels, Belgium
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132
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Cocco RE, Ucker DS. Distinct modes of macrophage recognition for apoptotic and necrotic cells are not specified exclusively by phosphatidylserine exposure. Mol Biol Cell 2001; 12:919-30. [PMID: 11294896 PMCID: PMC32276 DOI: 10.1091/mbc.12.4.919] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/1999] [Revised: 10/25/2000] [Accepted: 02/05/2001] [Indexed: 12/25/2022] Open
Abstract
The distinction between physiological (apoptotic) and pathological (necrotic) cell deaths reflects mechanistic differences in cellular disintegration and is of functional significance with respect to the outcomes that are triggered by the cell corpses. Mechanistically, apoptotic cells die via an active and ordered pathway; necrotic deaths, conversely, are chaotic and passive. Macrophages and other phagocytic cells recognize and engulf these dead cells. This clearance is believed to reveal an innate immunity, associated with inflammation in cases of pathological but not physiological cell deaths. Using objective and quantitative measures to assess these processes, we find that macrophages bind and engulf native apoptotic and necrotic cells to similar extents and with similar kinetics. However, recognition of these two classes of dying cells occurs via distinct and noncompeting mechanisms. Phosphatidylserine, which is externalized on both apoptotic and necrotic cells, is not a specific ligand for the recognition of either one. The distinct modes of recognition for these different corpses are linked to opposing responses from engulfing macrophages. Necrotic cells, when recognized, enhance proinflammatory responses of activated macrophages, although they are not sufficient to trigger macrophage activation. In marked contrast, apoptotic cells profoundly inhibit phlogistic macrophage responses; this represents a cell-associated, dominant-acting anti-inflammatory signaling activity acquired posttranslationally during the process of physiological cell death.
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Affiliation(s)
- R E Cocco
- Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60612, USA
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133
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Dao T, Exley M, Mehal WZ, Tahir SM, Snapper S, Taniguchi M, Balk SP, Crispe IN. Involvement of CD1 in peripheral deletion of T lymphocytes is independent of NK T cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:3090-7. [PMID: 11207260 DOI: 10.4049/jimmunol.166.5.3090] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
During peripheral T cell deletion, lymphocytes accumulate in nonlymphoid organs including the liver, a tissue that expresses the nonclassical, MHC-like molecule, CD1. Injection of anti-CD3 Ab results in T cell activation, which in normal mice is followed by peripheral T cell deletion. However, in CD1-deficient mice, the deletion of the activated T cells from the lymph nodes was impaired. This defect in peripheral T cell deletion was accompanied by attenuated accumulation of CD8(+) T cells in the liver. In tetra-parental bone marrow chimeras, expression of CD1 on the T cells themselves was not required for T cell deletion, suggesting a role for CD1 on other cells with which the T cells interact. We tested whether this role was dependent on the Ag receptor-invariant, CD1-reactive subset of NK T cells using two other mutant mouse lines that lack most NK T cells, due to deletion of the genes encoding either beta(2)-microglobulin or the TCR element J alpha 281. However, these mice had no abnormality of peripheral T cell deletion. These findings indicate a novel role for CD1 in T cell deletion, and show that CD1 functions in this process through mechanisms that does not involve the major, TCR-invariant set of NK T cells.
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MESH Headings
- Animals
- Antigens, CD1/genetics
- Antigens, CD1/physiology
- CD3 Complex/immunology
- CD4-CD8 Ratio
- Cell Death/immunology
- Cell Movement/immunology
- Cytotoxicity, Immunologic/genetics
- Down-Regulation/immunology
- Immune Sera/administration & dosage
- Injections, Intraperitoneal
- Killer Cells, Natural/cytology
- Killer Cells, Natural/immunology
- Killer Cells, Natural/metabolism
- Killer Cells, Natural/pathology
- Liver/immunology
- Liver/pathology
- Lymphocyte Activation/genetics
- Lymphopenia/genetics
- Lymphopenia/immunology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Receptors, Antigen, T-Cell/antagonists & inhibitors
- Receptors, Antigen, T-Cell/biosynthesis
- T-Lymphocyte Subsets/cytology
- T-Lymphocyte Subsets/immunology
- T-Lymphocyte Subsets/metabolism
- T-Lymphocyte Subsets/pathology
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Affiliation(s)
- T Dao
- Immunobiology Section, Yale University School of Medicine, New Haven, CT 06510, USA
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134
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Attinger A, MacDonald H, Acha-Orbea H. Lymphoid environment limits superantigen and antigen-induced T cell proliferation at high precursor frequency. Eur J Immunol 2001. [DOI: 10.1002/1521-4141(200103)31:3<884::aid-immu884>3.0.co;2-m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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135
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Pahlavani MA, Vargas DA. Aging but not dietary restriction alters the activation-induced apoptosis in rat T cells. FEBS Lett 2001; 491:114-8. [PMID: 11226431 DOI: 10.1016/s0014-5793(01)02184-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The aim of this study was to determine if aging or dietary restriction (DR) alters activation-induced cell death, which is known to regulate cell proliferation and eliminate the high number of activated cells during an immune response. Splenic T cells were isolated from young (4-6 months) and old (25-26 months) Fischer 344 rats that had free access to food, ad libitum (AL), and from dietary-restricted (DR) old (25-26 months) rats that beginning at 6 weeks of age were fed 60% (40% food-restricted) of the diet consume by the AL rats. T cells were incubated with anti-CD3 antibody, or staphylococcal enterotoxin B (primary stimulus) for 72-96 h, followed by restimulation with anti-CD3 (secondary stimulus) for 72 h. Activation-induced apoptosis was assessed by DNA fragmentation and the expression of Fas/CD95 receptor and Fas ligand (Fas-L) was measured by flow cytometry. We found that the amount of DNA fragmentation was significantly (P<0.05) higher in the stimulated and restimulated T cells from AL old rats and DR old rats compared to young rats. The increase in DNA fragmentation with age was paralleled by an increase in the proportion of the cells expressing Fas and Fas-L. However, DR had no significant effect on the age-related increase in DNA fragmentation or the expression of Fas or Fas-L. We also measured the levels of Bcl-2 and Bax protein and found that the level of Bcl-2 decreased and Bax increased with age and that DR had no effect on the age-related changes in the level of Bcl-2 or Bax protein. These results demonstrate that aging but not DR alters activation-induced apoptosis in rat T cells.
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Affiliation(s)
- M A Pahlavani
- Geriatric Research, Education, and Clinical Center (182), South Texas Veterans Health Care System, Audie L. Murphy Veterans Hospital, San Antonio, TX 78284, USA.
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136
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Wekerle T, Kurtz J, Sayegh M, Ito H, Wells A, Bensinger S, Shaffer J, Turka L, Sykes M. Peripheral deletion after bone marrow transplantation with costimulatory blockade has features of both activation-induced cell death and passive cell death. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:2311-6. [PMID: 11160287 DOI: 10.4049/jimmunol.166.4.2311] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Two major pathways of death of previously activated T cells have been described: activation-induced cell death can be triggered by restimulating activated T cells with high concentrations of Ag, is Fas-dependent, is not influenced by proteins of the Bcl family, and is blocked by cyclosporin A; in contrast, passive cell death is induced by the withdrawal of growth factors and activation stimuli, is Fas-independent, and is blocked by Bcl family proteins. We examined the role of these two forms of cell death in the peripheral deletion of donor-reactive host T cells after allogeneic bone marrow transplantation and costimulatory blockade with anti-CD154 plus CTLA4Ig in two murine models. The substantial decline in donor-reactive CD4 cells seen in wild-type recipients 1 wk after bone marrow transplantation with costimulatory blockade was largely inhibited in Fas-deficient recipients and in Bcl-x(L)-transgenic recipients. We observed these effects both in a model involving low-dose total body irradiation and a conventional dose of bone marrow, and in a radiation-free regimen using high-dose bone marrow transplantation. Furthermore, cyclosporin A did not completely block the deletion of donor-reactive CD4(+) T cells in recipients of bone marrow transplantation with costimulatory blockade. Thus, the deletion of donor-reactive T cells occurring early after bone marrow transplantation with costimulatory blockade has features of both activation-induced cell death and passive cell death. Furthermore, these in vivo data demonstrate for the first time the significance of in vitro results indicating that proteins of the Bcl family can prevent Fas-mediated apoptosis under certain circumstances.
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Affiliation(s)
- T Wekerle
- BMT Section, Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA
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137
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Utting O, Priatel JJ, Teh SJ, Teh HS. p59fyn (Fyn) promotes the survival of anergic CD4-CD8- alpha beta TCR+ cells but negatively regulates their proliferative response to antigen stimulation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:1540-6. [PMID: 11160194 DOI: 10.4049/jimmunol.166.3.1540] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
T cell anergy is characterized by alterations in TCR signaling that may play a role in controlling the unresponsiveness of the anergic cell. We have addressed questions regarding the importance of the Src kinase p59(fyn) (Fyn) in this process by using Fyn null mice. We demonstrate that a mature population of CD4(-)CD8(-) alphabeta TCR(+) anergic T cells lacking Fyn have a substantial recovery of their proliferation defect in response to Ag stimulation. This recovery cannot be explained by ameliorated production of IL-2, and the improved proliferation correlates with an enhanced ability of the Fyn(-/-) anergic T cells to up-regulate the high affinity IL-2 receptor. We also observe that anergic CD4(-)CD8(-) alphabeta TCR(+) T cells have a heightened survival ability that is partially dependent on the elevated levels of Fyn and IL-2 receptor beta-chain expressed by these cells. The enhanced survival correlates with an increased capacity of the anergic cells to respond to IL-15. We conclude that Fyn plays an important role in aspects of T cell anergy pertaining to TCR signaling and to cell survival.
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MESH Headings
- Animals
- Antigens/immunology
- CD4 Antigens/biosynthesis
- CD8 Antigens/biosynthesis
- Cell Survival/genetics
- Cell Survival/immunology
- Cells, Cultured
- Clonal Anergy/genetics
- Down-Regulation/genetics
- Down-Regulation/immunology
- H-2 Antigens/genetics
- Histocompatibility Antigen H-2D
- Interleukin-15/metabolism
- Interleukin-15/physiology
- Interleukin-2/biosynthesis
- Interleukin-2/metabolism
- Interleukin-2/physiology
- Lymphocyte Activation/genetics
- Mice
- Mice, Inbred C57BL
- Mice, Inbred DBA
- Mice, Knockout
- Mice, Transgenic
- Proto-Oncogene Proteins/deficiency
- Proto-Oncogene Proteins/genetics
- Proto-Oncogene Proteins/physiology
- Proto-Oncogene Proteins c-fyn
- Receptors, Antigen, T-Cell, alpha-beta/biosynthesis
- Receptors, Antigen, T-Cell, alpha-beta/genetics
- Receptors, Interleukin-2/biosynthesis
- Receptors, Interleukin-2/metabolism
- T-Lymphocyte Subsets/cytology
- T-Lymphocyte Subsets/enzymology
- T-Lymphocyte Subsets/immunology
- T-Lymphocyte Subsets/metabolism
- Up-Regulation/genetics
- Up-Regulation/immunology
- src-Family Kinases/deficiency
- src-Family Kinases/genetics
- src-Family Kinases/physiology
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Affiliation(s)
- O Utting
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
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138
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De Panfilis G, Caruso A, Sansoni P, Pasolini G, Semenza D, Torresani C. Identification of Fas-L-expressing apoptotic T lymphocytes in normal human peripheral blood : in vivo suicide. THE AMERICAN JOURNAL OF PATHOLOGY 2001; 158:387-91. [PMID: 11159176 PMCID: PMC1850331 DOI: 10.1016/s0002-9440(10)63981-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Fas-L molecules expressed by in vitro stimulated T cells may be critically involved in suicidal activation-induced cell death (AICD) of such cells through engagement of their Fas receptors. A similar suicide of T cells was postulated to occur even in vivo, to eliminate dangerous activated lymphocytes; however, the demonstration of suicidal AICD of T cells in healthy humans in vivo is still lacking. We therefore investigated the possible occurrence of Fas-L-linked suicidal apoptosis of T cells in normal human peripheral blood. For this purpose, we took advantage of immunoelectron microscopy, which allows simultaneous visualization of the morphological apoptotic cellular changes together with surface expression of Fas-L molecules. Very few T lymphocytes were observed showing the ultrastructural features of apoptotic lymphocytes; these occasional apoptotic T cells, together with the majority of the normal T cell population, expressed the Fas molecule on the plasma membrane, as expected. Interestingly, the apoptotic cells were also Fas-L-positive, whereas normal T cells were Fas-L-negative. Such Fas-L-associated T cell suicide operating in vivo in healthy individuals is presumably able to suppress immune responses and prevent autoreactivity, thus maintaining the homeostasis of human blood.
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Affiliation(s)
- G De Panfilis
- Department of Dermatology, Brescia University Hospital, Brescia, Italy
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139
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Izeradjene K, Revillard JP. Apoptosis of superantigen-activated T cells induced by mycophenolate mofetil treatment. Transplantation 2001; 71:118-25. [PMID: 11211176 DOI: 10.1097/00007890-200101150-00019] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND Mycophenolate mofetil (MMF), an ester prodrug of mycophenolic acid (MPA), is a potent immunosuppressive agent used in clinical organ transplantation. MPA preferentially inhibits the type II isoform of inosine monophosphate dehydrogenase, depletes GTP, suppresses transfer of mannose and fucose to glycoproteins, and prevents lymphocyte proliferation in vivo. Whether MMF can also delete activated T cells in vivo by triggering an apoptotic signal was addressed in this study. To this end we analyzed the activity of MMF in mice injected with the bacterial superantigen staphylococcal enterotoxin B (SEB). Superantigens bind to MHC class II molecules without requirement for processing, and activate subsets of CD4+ and CD8+ T cells whose T cell receptor beta chains express Vbeta family-specific homologous sequences. This model that shares several features with direct allorecognition has the unique advantage of allowing a precise monitoring of activated T cells. METHODS BALB/c mice treated with MMF (100 mg/kg/ day) or vehicle were injected with SEB. Serum cytokines, CD4+ and CD8+ Vbeta8+ cells were monitored in blood and lymphoid tissues, and apoptosis was determined by externalization of membrane phosphatidyl serine, double strand DNA breaks, and expression of B220 antigen by Vbeta8+ cells. RESULTS MMF treatment decreased tumor necrosis factor alpha, interferon gamma, and interleukin-10 secretion induced by SEB. It did not modify other early activation events (blast transformation, CD69 and CD25 expression) but completely inhibited SEB-induced expansion of Vbeta8+ cells by inducing apoptosis of SEB-reactive T cells. A similar effect was observed in CD95-ligand-deficient mice. Repeated SEB injections associated with MMF resulted in a marked decrease of CD8+ Vbeta8+ T cells. SEB-induced increase of Vbeta8+ thymocytes was not prevented by MMF treatment. CONCLUSION Results obtained in this in vivo model suggest that MMF treatment may induce deletion of activated peripheral T cells and decrease early cytokine responses.
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Affiliation(s)
- K Izeradjene
- Laboratory of Immunopharmacology, Institut National de la Santé et de la Recherche Médicale U 503, Claude Bernard University, Hopital E Herriot, Lyon, France
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140
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Gonzalo JA, Delaney T, Corcoran J, Goodearl A, Gutierrez-Ramos JC, Coyle AJ. Cutting edge: the related molecules CD28 and inducible costimulator deliver both unique and complementary signals required for optimal T cell activation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:1-5. [PMID: 11123268 DOI: 10.4049/jimmunol.166.1.1] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Optimal T cell activation requires engagement of CD28 with its counterligands B7-1 and B7-2. Inducible costimulator (ICOS) is the third member of the CD28/CTLA4 family that binds a B7-like protein, B7RP-1. Administration of ICOS-Ig attenuates T cell expansion following superantigen (SAg) administration, but fails to regulate either peripheral deletion or anergy induction. ICOS-Ig, but not CTLA4-Ig, uniquely regulates SAg-induced TNF-alpha production, whereas IL-2 secretion is modulated by CTLA4-Ig, but not ICOS-Ig. In contrast, both ICOS and CD28 are required for complete attenuation of IL-4 production. Our data suggest that ICOS and CD28 regulate T cell expansion and that ligation of either CD28 or ICOS can either uniquely regulate cytokine production (IL-2/TNF-alpha) or synergize for optimal cytokine production (IL-4) after SAg administration.
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MESH Headings
- Abatacept
- Adjuvants, Immunologic/physiology
- Animals
- Antigens, Bacterial/administration & dosage
- Antigens, Bacterial/pharmacology
- Antigens, CD
- Antigens, Differentiation/pharmacology
- Antigens, Differentiation, T-Lymphocyte/physiology
- CD28 Antigens/physiology
- CTLA-4 Antigen
- Cells, Cultured
- Clonal Anergy/immunology
- Clonal Deletion/immunology
- Cytokines/antagonists & inhibitors
- Cytokines/biosynthesis
- Enterotoxins/administration & dosage
- Enterotoxins/pharmacology
- Immunoconjugates
- Inducible T-Cell Co-Stimulator Protein
- Injections, Intravenous
- Lymphocyte Activation/immunology
- Mice
- Mice, Inbred BALB C
- Receptors, Antigen, T-Cell, alpha-beta/biosynthesis
- Signal Transduction/immunology
- Staphylococcus aureus/immunology
- T-Lymphocytes/immunology
- T-Lymphocytes/metabolism
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Affiliation(s)
- J A Gonzalo
- Department of Biology, Inflammation Division, Millennium Pharmaceuticals, Cambridge, MA 02139, USA
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141
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Yurovsky VV, Cottler-Fox MH, Atamas SP, Shanholtz CB, Britt EJ, Sensenbrenner LL, White B. Pulmonary T cell repertoire in patients with graft-versus-host disease following blood and marrow transplantation. Am J Hematol 2001; 66:1-11. [PMID: 11426485 DOI: 10.1002/1096-8652(200101)66:1<1::aid-ajh1000>3.0.co;2-r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Pulmonary inflammation is one of the risk factors associated with blood and marrow transplantation (BMT). To determine the potential role of T cells in pulmonary complications after transplantation, we analyzed the T-cell repertoire expressed in bronchoalveolar lavage fluids from eleven patients with graft-versus-host disease following BMT. A reverse transcriptase-polymerase chain reaction was used to amplify rearranged TCR transcripts in unfractionated, CD4+, and CD8+ T cells from bronchoalveolar lavage fluids. The relative expression of TCR variable (V) gene families and the diversity of junctional region lengths associated with different AV and BV gene families were analyzed. Nearly all TCR AV and BV gene families were detected in bronchoalveolar lavage cells from BMT recipients. Oligoclonal patterns of TCR junctional region lengths were observed in unfractionated, CD4+, and CD8+ bronchoalveolar T cells. The oligoclonal expansion of bronchoalveolar T cells in patients was confirmed by DNA sequencing. TCRV gene expression is almost completely restored in the lungs of BMT recipients as early as two weeks after transplantation. Increased oligoclonality among TCR gene families suggests either an incomplete restoration of TCR diversity or an antigen-driven expansion of T cells in the lungs of BMT recipients with graft-versus-host disease, not necessarily related to pulmonary infection.
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Affiliation(s)
- V V Yurovsky
- Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA.
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142
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Izeradjene K, Revillard JP, Genestier L. Inhibition of thymidine synthesis by folate analogues induces a Fas-Fas ligand-independent deletion of superantigen-reactive peripheral T cells. Int Immunol 2001; 13:85-93. [PMID: 11133837 DOI: 10.1093/intimm/13.1.85] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Methotrexate (MTX), a folate antagonist with multiple enzymatic targets, is used in the treatment of malignancies as well as in autoimmune and chronic inflammatory diseases, and ZD1694 (tomudex), a water-soluble quinazoline specific inhibitor of thymidylate synthase (TS), is used in the treatment of adenocarcinomas. In this study, we investigated the effects of these folate analogues on superantigen (SAg)-reactive peripheral T cells in vivo. In BALB/c mice, staphylococcal enterotoxin B (SEB)-induced cytokine secretion, IL-2R (CD25) expression and early deletion of a fraction of SEB-reactive V(beta)8(+) T cells were not impaired by either MTX (7 mg/kg/day) or tomudex (5 mg/kg/day). However, both MTX and tomudex prevented V(beta)8-selective T cell expansion and accelerated their peripheral elimination. Administration of thymidine (500 mg/kg/12 h) completely abrogated this effect, indicating that inhibition of TS but not that of other folate-dependent enzymes was the main mechanism involved. Furthermore, a marked increase of apoptotic cells restricted to the V(beta)8(+) T cell subset indicated that proliferation inhibition was associated with apoptosis. In contrast with peripheral V(beta)8(+) T cell deletion, MTX and tomudex did not prevent the increase of V(beta)8(+) thymocytes triggered by SEB. Experiments in C57BL/6-lpr/lpr mice further demonstrated that deletion of V(beta)8(+) T cells induced by folate analogues was independent of Fas-Fas ligand interaction. Our results provide evidence that folate analogues may selectively delete dividing peripheral T cells through TS inhibition, but do not interfere with other events triggered by SAg.
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Affiliation(s)
- K Izeradjene
- Laboratory of Immunopharmacology, Institut National de la Santé et de la Recherche Médicale U503, Claude Bernard University, Hopital E. Herriot, 5 Place d'Arsonval, 69437 Lyon Cedex 03, France
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143
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Dmoszynska A, Podhorecka M, Khmaj A, Surdacka A, Walter-Croneck A, Rolinski J. Short Communication: Expression of Apoptosis Regulating Factors on T Lymphocytes in Multiple Myeloma Patients. ACTA ACUST UNITED AC 2001; 6:393-7. [PMID: 27405696 DOI: 10.1080/10245332.2001.11746595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Multiple myeloma (MM) is a malignant proliferation of plasma cells in which dysregulation of programmed cell death (apoptosis) is responsible for tumor cell expansion. However some phenotypic and functional alterations of T cells in MM patients have been reported, that also can influence the plasma cell growth. The aim of the study was to assess some aspects of T lymphocyte apoptosis in MM to obtain a better understanding of the changes in the immune system in this disease. Flow cytometry was used to analyze the expression of two main regulators of apoptosis: the pro-apoptotic Fas antigen and the anti-apoptotic protein BCL-2 in patients with untreated MM and in healthy controls. ELISA was used to determine soluble Fas ligand (sFasL) serum levels in patients and control groups. We detected statistically significant higher Fas expression in patients than in controls both on CD4 and CD8 lymphocytes, but no differences in BCL-2 expression by these cells. The sFasL level was statistically significant lower in patients than in controls. Our results indicate that T cells in MM are controlled by up-regulation of Fas. The Fas/FasL system induces the killing of T cells expressing Fas antigen, what could account for the incapability of the immune system to protect host against tumor expansion.
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Affiliation(s)
- A Dmoszynska
- a Department of Haematology , University School of Medicine , Lublin , Poland
| | - M Podhorecka
- b Department of Clinical Immunology , University School of Medicine , Lublin , Poland
| | - A Khmaj
- a Department of Haematology , University School of Medicine , Lublin , Poland
| | - A Surdacka
- a Department of Haematology , University School of Medicine , Lublin , Poland
| | - A Walter-Croneck
- b Department of Clinical Immunology , University School of Medicine , Lublin , Poland
| | - J Rolinski
- a Department of Haematology , University School of Medicine , Lublin , Poland
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144
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Takenaka K, Fujiyama Y, Andoh A, Sasaki T, Amakata Y, Matsubara H, Hodohara K, Bamba T. Prevention of murine acute graft-versus-host disease by staphylococcal enterotoxin B treatment. Clin Exp Immunol 2001; 123:155-61. [PMID: 11168013 PMCID: PMC1905963 DOI: 10.1046/j.1365-2249.2001.01426.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Retroviral superantigens such as minor lymphocyte stimulating (Mls) antigen play an important role in the pathogenesis of acute graft-versus-host disease (GVHD). However, it remains unclear how exogenous bacterial superantigens modulate acute GVHD. In this study, we tested the effects of staphylococcal enterotoxin B (SEB) on the development of acute GVHD in a model involving the systemic transfer of parental C57Bl/6 spleen cells into BDF1 mice. SEB treatment suppressed the expansion of donor-derived T cells and blocked the decrease in the number of host cells. Impaired haematopoiesis was actually rescued by treatment with SEB. In SEB-treated mice, both spontaneous proliferation and IL-2 production in T cells were suppressed on day 2 after parental cell infusion. On day 21, the number of donor-derived CD4+ Vbeta8+ T cells markedly decreased in the spleen of SEB-treated mice. Donor-derived CD4+ T cells failed to proliferate in response to host alloantigens, and both donor- and host-derived T cells were unable to produce IL-2 in response to concanavalin A stimulation, suggesting that SEB treatment induced a general immunosuppressive state. Our results indicate that SEB treatment prevents the development of acute GVHD by leading to unresponsiveness of donor-derived T cells against host alloantigens in a Vbeta-restricted and unrestricted manner.
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MESH Headings
- Acute Disease
- Animals
- Cell Division/immunology
- Cells, Cultured
- Cytotoxicity Tests, Immunologic
- Disease Models, Animal
- Enterotoxins/administration & dosage
- Enterotoxins/therapeutic use
- Female
- Graft vs Host Disease/blood
- Graft vs Host Disease/immunology
- Graft vs Host Disease/pathology
- Graft vs Host Disease/prevention & control
- Hematopoiesis/immunology
- Immunosuppressive Agents/administration & dosage
- Injections, Intraperitoneal
- Lymphocyte Activation/immunology
- Lymphocyte Depletion
- Mice
- Mice, Inbred C57BL
- Mice, Inbred DBA
- Receptors, Antigen, T-Cell, alpha-beta/antagonists & inhibitors
- Receptors, Antigen, T-Cell, alpha-beta/biosynthesis
- Staphylococcus aureus/immunology
- T-Lymphocyte Subsets/immunology
- T-Lymphocyte Subsets/metabolism
- T-Lymphocyte Subsets/pathology
- T-Lymphocytes, Cytotoxic/immunology
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Affiliation(s)
- K Takenaka
- Department of Internal Medicine, Medical Coordination Centre and Blood Services Division,Shiga University of Medical Science, Seta-Tukinowa, Otsu, Japan
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145
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Uncovering the Differences between T Cell Tolerance and Immunity. Autoimmunity 2001. [DOI: 10.1007/978-94-010-0981-2_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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146
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Noorchashm H, Moore DJ, Noto LE, Noorchashm N, Reed AJ, Reed AL, Song HK, Mozaffari R, Jevnikar AM, Barker CF, Naji A. Impaired CD4 T cell activation due to reliance upon B cell-mediated costimulation in nonobese diabetic (NOD) mice. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:4685-96. [PMID: 11035112 DOI: 10.4049/jimmunol.165.8.4685] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Diabetes in nonobese diabetic (NOD) mice results from the activation of I-A(g7)-restricted, islet-reactive T cells. This study delineates several characteristics of NOD CD4 T cell activation, which, independent of I-A(g7), are likely to promote a dysregulated state of peripheral T cell tolerance. NOD CD4 T cell activation was found to be resistant to antigenic stimulation via the TCR complex, using the progression of cell division as a measure. The extent of NOD CD4 T cell division was highly sensitive to changes in Ag ligand density. Moreover, even upon maximal TCR complex-mediated stimulation, NOD CD4 T cell division prematurely terminated. Maximally stimulated NOD CD4 T cells failed to achieve the threshold number of division cycles required for optimal susceptibility to activation-induced death, a critical mechanism for the regulation of peripheral T cell tolerance. Importantly, these aberrant activation characteristics were not T cell-intrinsic but resulted from reliance on B cell costimulatory function in NOD mice. Costimulation delivered by nonautoimmune strain APCs normalized NOD CD4 T cell division and the extent of activation-induced death. Thus, by disrupting the progression of CD4 T cell division, polarization of APC costimulatory function to the B cell compartment could allow the persistence and activation of diabetogenic cells in NOD mice.
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Affiliation(s)
- H Noorchashm
- Department of Surgery, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA
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147
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Abstract
Immune responses are by necessity highly regulated to achieve the appropriate balance of aggression and restraint. Among the many factors involved in maintaining this balance are the interactions between accessory molecule receptors expressed on T cells and their ligands on antigen-presenting cells. Our studies during the past several years have focused on defining how particular accessory molecule interactions influence the activation of naïve CD4+ T cells and the subsequent development of effector function. In this article, we discuss our findings on the effects of distinct accessory molecules with particular attention to the unique roles of LFA-1 and CD28 during different phases of the naïve CD4+ cell response.
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Affiliation(s)
- M E Ozaki
- Department of Immunology, The Scripps Research Institute, La Jolla, CA 92037, USA
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148
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Canalejo A, Almadén Y, Torregrosa V, Gomez-Villamandos JC, Ramos B, Campistol JM, Felsenfeld AJ, Rodríguez M. The in vitro effect of calcitriol on parathyroid cell proliferation and apoptosis. J Am Soc Nephrol 2000; 11:1865-1872. [PMID: 11004217 DOI: 10.1681/asn.v11101865] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Calcitriol treatment is used to reduce parathyroid hormone levels in azotemic patients with secondary hyperparathyroidism (HPT). Whether long-term calcitriol administration reduces parathyroid gland size in patients with severe secondary hyperparathyroidism is not clear. The aim of the study was to evaluate in vitro the effect of calcitriol on parathyroid cell proliferation and apoptosis in normal parathyroid glands and in adenomatous and hyperplastic human parathyroid glands. Freshly harvested parathyroid glands from normal dogs and hyperplastic and adenomatous glands from patients with secondary (2 degrees) and primary (1 degree) HPT undergoing parathyroidectomy were studied. Flow cytometry was used to quantify the cell cycle and apoptosis of parathyroid cells. Apoptosis was also evaluated by DNA electrophoresis and light and electron microscopy. In normal dog parathyroid glands, culture with calcitriol (10(-10) to 10(-7) M) for 24 h produced a dose-dependent inhibitory effect on the progression of cells into the cell cycle and into apoptosis. When glands from patients with 2 degrees HPT were cultured for 24 h, only high calcitriol concentrations (10(-7) M) inhibited the progression through the cell cycle and the induction of apoptosis. In parathyroid adenomas (1 degrees HPT), even a high concentration of calcitriol (10(-7) M) had no significant effect on the cell cycle or apoptosis. The present study shows that in vitro, calcitriol inhibits in a dose-dependent manner in normal parathyroid glands both parathyroid cell proliferation and apoptosis. However, in secondary hyperplasia, only high concentrations of calcitriol inhibited cell proliferation and apoptosis. In 1 degree HPT, even high concentrations of calcitriol had no effect. Because calcitriol simultaneously inhibits both cell proliferation and apoptosis, a reduction in the parathyroid gland mass may not occur as a direct effect of calcitriol treatment.
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Affiliation(s)
- Antonio Canalejo
- Research Unit and Nephrology Service, Reina Sofia University Hospital, Córdoba
| | - Yolanda Almadén
- Research Unit and Nephrology Service, Reina Sofia University Hospital, Córdoba
| | | | | | - Blanca Ramos
- Nephrology Service, Carlos Haya Hospital, Malaga, Spain
| | | | - Arnold J Felsenfeld
- Department of Medicine, West Los Angeles VA Medical Center and UCLA, Los Angeles, California
| | - Mariano Rodríguez
- Research Unit and Nephrology Service, Reina Sofia University Hospital, Córdoba
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149
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Abstract
Ion fluxes and volume changes of the whole cell as well as of organelles belong to the hallmarks of apoptosis; however, the molecular mechanism regulating these changes is only poorly characterized. Several ion channels in the plasma membrane, in particular the N-type K(+) channel, the chloride channel cystic fibrosis conductance regulator, and an outward rectifying chloride channel, as well as the mitochondrial permeability transition pore, have been implicated to be involved in signal transduction cascades regulating apoptosis. Furthermore, Bcl-2-like proteins have been suggested to function, at least in part, as ion channels, because they display some homology to bacterial pore-forming toxins. In contrast to the demonstration of the involvement of these different ion channels in apoptosis, the molecular consequences regulated by these ion channels, and finally triggering apoptosis, are almost completely unknown.
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Affiliation(s)
- E Gulbins
- Department of Physiology, University of Tuebingen, 72076 Tuebingen, Germany.
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150
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Abstract
Rejection of fully MHC-mismatched allografts entails the direct recognition of donor MHC molecules (direct antigen presentation) and the activation of an unusually large mass of alloreactive T cells. There is compelling evidence that apoptotic cell death of activated T cells is a critical initial step in the induction of peripheral allograft tolerance with regimens that are not inherently lymphoablative and that therapies that block T cell activation and T cell apoptosis also block the acquisition of tolerance. Thus, T cell apoptosis may play an important role in reducing the size of cytopathic T cell clones and this process may also promote the development and expansion of immune regulatory cells that are essential in the maintenance of allograft tolerance.
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Affiliation(s)
- X C Li
- Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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