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Li H, Zhao Y, Guo Y, Li Z, Eisele L, Mourad W. Zinc induces dimerization of the class II major histocompatibility complex molecule that leads to cooperative binding to a superantigen. J Biol Chem 2006; 282:5991-6000. [PMID: 17166841 PMCID: PMC3924565 DOI: 10.1074/jbc.m608482200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Dimerization of class II major histocompatibility complex (MHC) plays an important role in the MHC biological function. Mycoplasma arthritidis-derived mitogen (MAM) is a superantigen that can activate large fractions of T cells bearing specific T cell receptor Vbeta elements. Here we have used structural, sedimentation, and surface plasmon resonance detection approaches to investigate the molecular interactions between MAM and the class II MHC molecule HLA-DR1 in the context of a hemagglutinin peptide-(306-318) (HA). Our results revealed that zinc ion can efficiently induce the dimerization of the HLA-DR1/HA complex. Because the crystal structure of the MAM/HLA-DR1/hemagglutinin complex in the presence of EDTA is nearly identical to the structure of the complex crystallized in the presence of zinc ion, Zn(2+) is evidently not directly involved in the binding between MAM and HLA-DR1. Sedimentation and surface plasmon resonance studies further revealed that MAM binds the HLA-DR1/HA complex with high affinity in a 1:1 stoichiometry, in the absence of Zn(2+). However, in the presence of Zn(2+), a dimerized MAM/HLA-DR1/HA complex can arise through the Zn(2+)-induced DR1 dimer. In the presence of Zn(2+), cooperative binding of MAM to the DR1 dimer was also observed.
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Affiliation(s)
- Hongmin Li
- Wadsworth Center, New York State Department of Health, University of Albany, State University of New York, Albany, New York 12208, USA.
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2
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Gross U, Schroder AK, Haylett RS, Arlt S, Rink L. The superantigen staphylococcal enterotoxin A (SEA) and monoclonal antibody L243 share a common epitope but differ in their ability to induce apoptosis via MHC-II. Immunobiology 2006; 211:807-14. [PMID: 17113918 DOI: 10.1016/j.imbio.2006.05.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2005] [Revised: 05/16/2006] [Accepted: 05/18/2006] [Indexed: 12/13/2022]
Abstract
Crosslinking of MHC class II (MHC-II) molecules by antibodies or by superantigens (SAg) induces a variety of functional responses in the antigen presenting cell. We were able to allocate K39 as the residue that is essential for binding of antibody L243 to the alpha chain of HLA-DR. K39 is also essential for binding of staphylococcal enterotoxin A (SEA). However, the functional responses of the two ligands differ considerably exemplified by the ability of L243 to induce apoptosis in monocytic cells and in B cells, whereas SEA is unable to activate the apoptosis pathway. Despite the differences in functional responses, both ligands induce cell aggregation in MonoMac-1 cells. The SEA molecule with its two different binding sites associates one MHC alpha chain with one beta chain as opposed to two alpha chains that are brought into close proximity by the two identical antigen binding sites of L243. We therefore conclude that the spatial orientation of dimerized MHC-II and their associated proteins is an important factor for the nature of the transduced signal and consequently the outcome of functional responses.
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Affiliation(s)
- Ulrike Gross
- Institute of Immunology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074 Aachen, Germany
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3
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Li H, Zhao Y, Guo Y, VanVranken SJ, Li Z, Eisele L, Mourad W. Mutagenesis, biochemical, and biophysical characterization of Mycoplasma arthritidis-derived mitogen. Mol Immunol 2006; 44:763-73. [PMID: 16753217 PMCID: PMC3923304 DOI: 10.1016/j.molimm.2006.04.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2006] [Accepted: 04/11/2006] [Indexed: 02/02/2023]
Abstract
Mycoplasma arthritidis-derived mitogen (MAM) is a superantigen (SAg) that can activate large fractions of T cells bearing particular TCR Vbeta elements. Here we report the mutagenesis, biochemical and biophysical studies on the dimerization of MAM in solution. Our studies showed that although MAM mainly exists as a monomer in solution, a small percentage of MAM molecules form homodimer at high protein concentration, regardless of the presence of Zn2+. A distinct peak corresponding to a MAM homodimer was detected in the presence of EDTA, using both chemical cross-linking and analytical ultracentrifugation methods. Further mutagenesis studies revealed that single mutation of residues at the interface of the crystallographic dimer of MAM does not significantly affect the dimerization of MAM in solution. Circular dichroism (CD) analysis indicated that addition of Zn2+ does not induce conformational changes of MAM from its apo-state. Thermal denaturation experiments indicated that addition of Zn2+ to MAM solution resulted in a decrease of melting point (Tm), whereas addition of EDTA did not affect the Tm of MAM. These results imply that there is no defined Zn2+-binding site on MAM.
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Affiliation(s)
- Hongmin Li
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
- Department of Biomedical Sciences, School of Public Health, University at Albany, State University of New York, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
- Corresponding author. Tel.: +1 518 486 9154; fax: +1 518 474 7992. (H. Li)
| | - Yiwei Zhao
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
| | - Yi Guo
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
| | - Sandra J. VanVranken
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
| | - Zhong Li
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
| | - Leslie Eisele
- Wadsworth Center, New York State Department of Health, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, United States
| | - Walid Mourad
- Université de Montreal, CHUM, Campus St-Luc, PEA, 264, Boul. René Lévesque Est, Bureau 313, Montréal, Qué. H2X 1P1, Canada
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4
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Zhao Y, Li Z, Drozd SJ, Guo Y, Mourad W, Li H. Crystal structure of Mycoplasma arthritidis mitogen complexed with HLA-DR1 reveals a novel superantigen fold and a dimerized superantigen-MHC complex. Structure 2004; 12:277-88. [PMID: 14962388 PMCID: PMC3923524 DOI: 10.1016/j.str.2004.01.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2003] [Revised: 10/15/2003] [Accepted: 10/16/2003] [Indexed: 01/24/2023]
Abstract
Mycoplasma arthritidis-derived mitogen (MAM) is a superantigen that can activate large fractions of T cells bearing particular TCR Vbeta elements. Here we report the crystal structure of MAM complexed with a major histocompatibility complex (MHC) antigen, HLA-DR1, loaded with haemagglutinin peptide 306-318 (HA). The structure reveals that MAM has a novel fold composed of two alpha-helical domains. This fold is entirely different from that of the pyrogenic superantigens, consisting of a beta-grasped motif and a beta barrel. In the complex, the N-terminal domain of MAM binds orthogonally to the MHC alpha1 domain and the bound HA peptide, and to a lesser extent to the MHC beta1 domain. Two MAM molecules form an asymmetric dimer and cross-link two MHC antigens to form a plausible, dimerized MAM-MHC complex. These data provide the first crystallographic evidence that superantigens can dimerize MHC molecules. Based on our structure, a model of the TCR2MAM2MHC2 complex is proposed.
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Affiliation(s)
- Yiwei Zhao
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
| | - Zhong Li
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
| | - Sandra J. Drozd
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
| | - Yi Guo
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
| | - Walid Mourad
- Centre de Recherche en Immunologie, et Rhumatologie, CHUQ, Pavillon CHUL, Université Laval, Québec, Québec G1V-4G2, Canada
| | - Hongmin Li
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
- Department of Biomedical Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201
- Correspondence:
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5
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Langlois MA, El Fakhry Y, Mourad W. Zinc-binding sites in the N terminus of Mycoplasma arthritidis-derived mitogen permit the dimer formation required for high affinity binding to HLA-DR and for T cell activation. J Biol Chem 2003; 278:22309-15. [PMID: 12676930 DOI: 10.1074/jbc.m300823200] [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: 11/06/2022] Open
Abstract
Zinc-dependent superantigens can be divided into two subfamilies based on how they use zinc ions for interactions with major histocompatibility complex (MHC) class II molecules. Members of the first subfamily use zinc ions for interactions with histidine 81 on the beta-chain of MHC class II molecules, whereas members of the second subfamily use zinc ions for dimer formation. The zinc-binding motif is located in the C terminus of the molecule in both subfamilies. While our recent studies with Mycoplasma arthritidis-derived mitogen (MAM) have provided the first direct evidence demonstrating the binding to MHC class II molecules in a zinc-dependent manner, it still not known how zinc coordinates the interaction. Data presented here show that the zinc ion is mainly required to induce MAM/MAM dimer formation. Residues in the N terminus of MAM are involved in dimer formation and MHC class II binding, while histidine 14 and aspartic acid 31 of the MAM sequence are the major residues mediating MAM/MAM dimerization. Zinc-induced dimer formation is necessary for MAM binding, MHC class II-induced cell-cell adhesion, and efficient T cell activation. Together these results depict the unique mode of interaction of MAM in comparison with other superantigens.
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Affiliation(s)
- Marc-André Langlois
- Centre de Recherche en Rhumatologie et Immunologie, Centre Hospitalier de l'université Laval, Faculté de Médecine, Université Laval, Quebec G1V 4G2, Canada
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6
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Ribeiro-Dias F, Shio MT, Timenetsky J, Oliane APC, Metran CC, Pessoa FB, Jancar S. Mycoplasma arthritidis superantigen (MAM)-induced macrophage nitric oxide release is MHC class II restricted, interferongamma dependent, and toll-like receptor 4 independent. Exp Cell Res 2003; 286:345-54. [PMID: 12749862 DOI: 10.1016/s0014-4827(03)00108-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mycoplasma arthritidis causes arthritis in rodents that resembles human rheumatoid arthritis. It produces a superantigen (MAM) that stimulates production of cytokines by making a bridge between lymphocyte T-cell receptor with the appropriate Vbeta chain, and H-2 1-Ealpha MHC class II molecules. Here we studied MAM-induced nitric oxide (NO) production in mouse peritoneal macrophages and found that it was: (1) time and concentration dependent, (2) possibly derived from inducible NOS synthase since it was reduced significantly by amino guanidine pretreatment, (3) restricted to H-2(K) (C3H/HePas and C3H/HeJ) and H-2(d) strains (BALB/c), (4) independent of TLR4 signaling since the coisogenic strains C3H/HePas and C3H/HeJ (TLR4 deficient) produced similar levels of NO following MAM stimulation, (5) potentiated by lipopolysaccharide, and (6) dependent on the presence of nonadherent peritoneal cells. Neutralization of interferon-gamma (IFNgamma in the peritoneal cell cultures with monoclonal antibodies abolished MAM-induced NO production. Addition of rIFNgamma to the adherent cells substituted the nonadherent cells for MAM-induced NO production. A macrophage cell line, J774A.1 (H-2(d)), also produced NO upon MAM stimulation but only when BALB/c spleen lymphocytes were added. Thus, in murine macrophages, MAM induces NO production that is dependent on signaling through MHC class II molecules and IFNgamma but independent of TLR4 expression.
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MESH Headings
- Animals
- Antigens
- Antigens, Bacterial
- Arthritis, Rheumatoid/immunology
- Arthritis, Rheumatoid/metabolism
- Cell Communication/immunology
- Cells, Cultured
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Histocompatibility Antigens Class II/drug effects
- Histocompatibility Antigens Class II/metabolism
- Interferon-gamma/metabolism
- Interferon-gamma/pharmacology
- Lymphocyte Activation/drug effects
- Lymphocyte Activation/immunology
- Lymphocytes/immunology
- Lymphocytes/metabolism
- Macrophages/drug effects
- Macrophages/metabolism
- Male
- Membrane Glycoproteins/drug effects
- Membrane Glycoproteins/metabolism
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C3H
- Mice, Inbred C57BL
- Mitogens/pharmacology
- Nitric Oxide/biosynthesis
- Nitric Oxide Synthase/drug effects
- Nitric Oxide Synthase/metabolism
- Proteins
- Receptors, Cell Surface/drug effects
- Receptors, Cell Surface/metabolism
- Signal Transduction/drug effects
- Signal Transduction/immunology
- Superantigens
- Toll-Like Receptor 4
- Toll-Like Receptors
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Affiliation(s)
- Fátima Ribeiro-Dias
- Immunology Section/DMIPP/IPTSP, Federal University of Goiás, Goiânia, Brazil
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7
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Bouillon M, El Fakhry Y, Girouard J, Khalil H, Thibodeau J, Mourad W. Lipid raft-dependent and -independent signaling through HLA-DR molecules. J Biol Chem 2003; 278:7099-107. [PMID: 12499388 DOI: 10.1074/jbc.m211566200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipid rafts are plasma membrane microdomains that are highly enriched in signaling molecules and that act as signal transduction platforms for many immune receptors. The involvement of these microdomains in HLA-DR-induced signaling is less well defined. We examined the constitutive presence of HLA-DR molecules in lipid rafts, their possible recruitment into these microdomains, and the role of these microdomains in HLA-DR-induced responses. We detected significant amounts of HLA-DR molecules in the lipid rafts of EBV(+) and EBV(-) B cell lines, monocytic cell lines, transfected HeLa cells, tonsillar B cells, and human monocytes. Localization of HLA-DR in these microdomains was unaffected by the deletion of the cytoplasmic domain of both the alpha and beta chains. Ligation of HLA-DR with a bivalent, but not a monovalent, ligand resulted in rapid tyrosine phosphorylation of many substrates, especially Lyn, and activation of ERK1/2 MAP kinase. However, the treatment failed to induce further recruitment of HLA-DR molecules into lipid rafts. The HLA-DR-induced signaling events were accompanied by the induction of cell-cell adhesion that could be inhibited by PTK and Lyn but not ERK1/2 inhibitors. Disruption of lipid rafts by methyl-beta-cyclodextrin (MbetaCD) resulted in the loss of membrane raft association with HLA-DR molecules, inhibition of HLA-DR-mediated protein tyrosine phosphorylation and cell-cell adhesion. MbetaCD did not affect the activation of ERK1/2, which was absent from lipid rafts. These results indicate that although all the HLA-DR-induced events studied are dependent on HLA-DR dimerization, some require the presence of HLA-DR molecules in lipid rafts, whereas others do not.
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Affiliation(s)
- Marlene Bouillon
- Centre de Recherche en Rhumatologie et Immunologie, (CHUL), Département de Médecine, Université Laval, Quebec City, Quebec G1V 4G2, Canada
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8
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Yang J, Hooper WC, Phillips DJ, Talkington DF. Regulation of proinflammatory cytokines in human lung epithelial cells infected with Mycoplasma pneumoniae. Infect Immun 2002; 70:3649-55. [PMID: 12065506 PMCID: PMC128054 DOI: 10.1128/iai.70.7.3649-3655.2002] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mycoplasma pneumoniae is a small bacterium without a cell wall that causes tracheobronchitis and atypical pneumonia in humans. It has also been associated with chronic conditions, such as arthritis, and extrapulmonary complications, such as encephalitis. Although the interaction of mycoplasmas with respiratory epithelial cells is a critical early phase of pathogenesis, little is known about the cascade of events initiated by infection of respiratory epithelial cells by mycoplasmas. Previous studies have shown that M. pneumoniae can induce proinflammatory cytokines in several different study systems including cultured murine and human monocytes. In this study, we demonstrate that M. pneumoniae infection also induces proinflammatory cytokine expression in A549 human lung carcinoma cells. Infection of A549 cells resulted in increased levels of interleukin-8 (IL-8) and tumor necrosis factor alpha mRNA, and both proteins were secreted into culture medium. IL-1 beta mRNA also increased after infection and IL-1 beta protein was synthesized, but it remained intracellular. In contrast, levels of IL-6 and gamma interferon mRNA and protein remained unchanged or undetectable. Using protease digestion and antibody blocking methods, we found that M. pneumoniae cytoadherence is important for the induction of cytokines. On the other hand, while M. pneumoniae protein synthesis and DNA synthesis do not appear to be prerequisites for the induction of cytokine gene expression, A549 cellular de novo protein synthesis is responsible for the increased cytokine protein levels. These results suggest a novel role for lung epithelial cells in the pathogenesis of M. pneumoniae infection and provide a better understanding of M. pneumoniae pathology at the cellular level.
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Affiliation(s)
- Jun Yang
- Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
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9
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Abstract
Superantigens (SAgs) are viral and bacterial proteins exhibiting a highly potent polyclonal lymphocyte-proliferating activity for CD4(+), CD8(+) and sometimes gammadelta(+) T cells of human and (or) various animal species. Unlike conventional antigens, SAgs bind as unprocessed proteins to invariant regions of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) and to particular motifs of the variable region of the beta chain (Vbeta) of T-cell receptor (TcR) outside the antigen-binding groove. As a consequence, SAgs stimulate at nano-to picogram concentrations up to 10 to 30% of host T-cell repertoire while only one in 10(5)-10(6) T cells (0.01-0.0001%) are activated upon conventional antigenic peptide binding to TcR. SAg activation of an unusually high percentage of T lymphocytes initiates massive release of pro-inflammatory and other cytokines which play a pivotal role in the pathogenesis of the diseases provoked by SAg-producing microorganisms. We briefly describe in this review the molecular and biological properties of the bacterial superantigen toxins and mitogens identified in the past decade.
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Affiliation(s)
- H Müller-Alouf
- Département de Microbiologie des Ecosystèmes, Institut Pasteur de Lille, Lille, France
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10
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Abstract
Zn is an essential trace element for all organisms. In human subjects body growth and development is strictly dependent on Zn. The nervous, reproductive and immune systems are particularly influenced by Zn deficiency, as well as by increased levels of Zn. The relationship between Zn and the immune system is complex, since there are four different types of influence associated with Zn. (1) The dietary intake and the resorption of Zn depends on the composition of the diet and also on age and disease status. (2) Zn is a cofactor in more than 300 enzymes influencing various organ functions having a secondary effect on the immune system. (3) Direct effects of Zn on the production, maturation and function of leucocytes. (4) Zn influences the function of immunostimulants used in the experimental systems. Here we summarize all four types of influence on the immune function. Nutritional aspects of Zn, the physiology of Zn, the influence of Zn on enzymes and cellular functions, direct effects of Zn on leucocytes at the cellular and molecular level, Zn-altered function of immunostimulants and the therapeutic use of Zn will be discussed in detail.
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Affiliation(s)
- L Rink
- Institute of Immunology and Transfusion Medicine, University of Lübeck School of Medicine, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
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11
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Abstract
Although the intriguing role of zinc as an essential trace element for immune function is well established, particular progress in determining the molecular principles of action of this ion was made recently. Leukocyte responsiveness is delicately regulated by zinc concentration. Zinc deficiency as well as supraphysiologic levels impair immune function. Furthermore, the activities of many immunostimulants frequently used in immunologic studies are influenced by zinc concentration. Therefore, our knowledge from in vitro studies is widely dependent on the zinc concentration, and when not in physiologic range, immunologic responses are artificially low. Decreased production of TH1 cytokines and interferon-alpha by leukocytes in the healthy elderly person is correlated with low zinc serum level. The defect in interferon-alpha production is reconstituted by the addition of physiologic amounts of zinc in vitro. Interestingly, zinc induces cytokine production by isolated leukocytes. Zinc induces monocytes to produce interleukin-1, interleukin-6 and tumor necrosis factor-alpha in peripheral blood mononuclear cells and separated monocytes. This effect is higher in serum-free medium. However, only in the presence of serum does zinc also induce T cells to produce lymphokines. This effect on T cells is mediated by cytokines produced by monocytes. Stimulation also requires cell-to-cell contact of monocytes and T cells. Information is presented to illustrate the concepts that the zinc concentration must be taken into account whenever in vitro studies are made or complex alterations of immune functions are observed in vivo.
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Affiliation(s)
- L Rink
- Institute of Immunology and Transfusion Medicine, University of Lübeck School of Medicine, Lübeck, Germany
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12
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13
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Guo W, Mourad W, Charron D, Al-Daccak R. Ligation of MHC class II molecules differentially upregulates TNF beta gene expression in B cell lines of different MHC class II haplotypes. Hum Immunol 1999; 60:312-22. [PMID: 10363722 DOI: 10.1016/s0198-8859(98)00131-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Although the production of selected cytokines by B cells is important for their regulation, little is known about MHC class II-induced cytokine expression in these cells. We designed the present studies to investigate MHC class II-mediated TNF-beta gene expression in 19 EBV-transformed homozygote B cell lines at similar stage of differentiation but presenting different MHC class II haplotypes. Our results demonstrate that in contrast to PMA, engagement of MHC class II with staphylococcal enterotoxin A (SEA), a natural ligand, or with anti-HLA-DR mAb L243, stimulates TNF-beta gene expression in some but not all B cell lines. The differential stimulation of TNF-beta gene expression via MHC class II was not due to the cells MHC class II expression level, nor to their capacity to bind the ligands as evidenced by SEA binding affinity studies. Together these results demonstrate that ligation of MHC class II molecules can stimulate TNF-beta gene expression in a B cell line-dependent manner. The differential cytokine gene expression might be due to an influence of MHC class II haplotype either by a linkage disequilibrium with TNF-beta gene or by a differential association with effector or cell surface molecules.
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Affiliation(s)
- W Guo
- Centre de Recherche en Rhumatologie et Immunologie, Le Centre Hospitalier de Québec, Sainte-Foy, Canada
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14
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Abstract
The recent sequencing of the entire genomes of Mycoplasma genitalium and M. pneumoniae has attracted considerable attention to the molecular biology of mycoplasmas, the smallest self-replicating organisms. It appears that we are now much closer to the goal of defining, in molecular terms, the entire machinery of a self-replicating cell. Comparative genomics based on comparison of the genomic makeup of mycoplasmal genomes with those of other bacteria, has opened new ways of looking at the evolutionary history of the mycoplasmas. There is now solid genetic support for the hypothesis that mycoplasmas have evolved as a branch of gram-positive bacteria by a process of reductive evolution. During this process, the mycoplasmas lost considerable portions of their ancestors' chromosomes but retained the genes essential for life. Thus, the mycoplasmal genomes carry a high percentage of conserved genes, greatly facilitating gene annotation. The significant genome compaction that occurred in mycoplasmas was made possible by adopting a parasitic mode of life. The supply of nutrients from their hosts apparently enabled mycoplasmas to lose, during evolution, the genes for many assimilative processes. During their evolution and adaptation to a parasitic mode of life, the mycoplasmas have developed various genetic systems providing a highly plastic set of variable surface proteins to evade the host immune system. The uniqueness of the mycoplasmal systems is manifested by the presence of highly mutable modules combined with an ability to expand the antigenic repertoire by generating structural alternatives, all compressed into limited genomic sequences. In the absence of a cell wall and a periplasmic space, the majority of surface variable antigens in mycoplasmas are lipoproteins. Apart from providing specific antimycoplasmal defense, the host immune system is also involved in the development of pathogenic lesions and exacerbation of mycoplasma induced diseases. Mycoplasmas are able to stimulate as well as suppress lymphocytes in a nonspecific, polyclonal manner, both in vitro and in vivo. As well as to affecting various subsets of lymphocytes, mycoplasmas and mycoplasma-derived cell components modulate the activities of monocytes/macrophages and NK cells and trigger the production of a wide variety of up-regulating and down-regulating cytokines and chemokines. Mycoplasma-mediated secretion of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6, by macrophages and of up-regulating cytokines by mitogenically stimulated lymphocytes plays a major role in mycoplasma-induced immune system modulation and inflammatory responses.
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Affiliation(s)
- S Razin
- Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
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15
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Abstract
In this paper I will discuss the possible role of sperm as cofactors in the genital-mucosal transmission of HIV. The ideas involved arose from my laboratory's discovery that sperm bind to HLA-DR molecules expressed on somatic cells, and from our subsequent findings that lymphocytes are activated by these interactions. Sperm binding to HLA-DR mimics one of the two ligand binding characteristics of superantigens, which also bind to T-cell receptors in a V-beta-specific fashion. This property of sperm may be significant in HIV transmission because: (a) HLA-DR plays a central role in immune recognition and response; and (b) cell interactions involving HLA-DR are involved in HIV infection and disease development. After sexual contact, sperm elicit a transient leukocytic infiltration of the mammalian cervix (Thompson, L.A., Barratt, C.L., Bolton, A.E., Cooke, I.D., 1992. The leukocytic reaction of the human cervix. Am. J. Reprod. Immunol. 28, 85; Pandya, I.J., Cohen, J., 1985. The leukocytic reaction of the human uterine cervix to sperm. Fertil. Steril. 43, 417), and human cervical cells are bound and penetrated by sperm at this time (Sievers-Altermann, R., Engelbrecht, D.V., 1990. Entry of spermatozoa into the cervical mucosa and transmission of the AIDS virus. S. Afr. Med. J. 77, 319). At present, little is known about these in vivo events, but sperm-somatic cell interactions in vitro are also followed by sperm entry into the target cell cytoplasm and target cell activation. When the target cells are leukocytes, sperm interactions increase their susceptibility to HIV infection. If similar interactions occur in the cervicovaginal environment after sexual contact, they are likely to enhance the genital-mucosal transfer of HIV from semen.
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Affiliation(s)
- V L Scofield
- Department of Biological Sciences, University of Southern California, Los Angeles 90089-2031, USA
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16
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Alvarez-Ossorio L, Johannsen M, Alvarez-Ossorio R, Nicklas W, Kirchner H, Rink L. Cytokine induction by Mycoplasma arthritidis-derived superantigen (MAS), but not by TSST-1 or SEC-3, is correlated to certain HLA-DR types. Scand J Immunol 1998; 47:43-7. [PMID: 9467657 DOI: 10.1046/j.1365-3083.1998.00252.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Superantigens bind to major histocompatibility complex (MHC) class II molecules on antigen presenting cells and T cells in a V beta-restricted manner. Both cell types are activated resulting in cytokine production. Although the MHC-II binding site for superantigens has been well described, little is known as to whether this binding complex has an influence on cytokine induction. In order to assess superantigen induced cytokine production and its correlation to HLA-DR types, the authors stimulated peripheral blood from 40 subjects with superantigens toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin C-3 (SEC-3) and Mycoplasma arthritidis-derived superantigen (MAS), and measured cytokine levels thereafter. The HLA-DR type was determined in each subject. A statistical evaluation was carried out between the highest superantigen cytokine induction and the presence of certain HLA-DR types. Whereas MAS presented a statistical association between the highest cytokine production with HLA-DR4, DR7 and DR12, no such associations were observed for TSST-1 and SEC-3. These results demonstrate that T cell stimulation, and consequently its cytokine production by MAS but not by TSST-1 and SEC-3, depends on the presenting HLA-DR type. Because the diverse HLA-DR specificities are given according to the variability of the beta chain of the HLA-DR molecule, the data suggest the participation of the human MHC-II beta chain in the MAS/MHC-II binding.
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Affiliation(s)
- L Alvarez-Ossorio
- Institute of Immunology and Transfusion Medicine, University of Lübeck School of Medicine, Germany
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Cole BC, Sawitzke AD, Ahmed EA, Atkin CL, David CS. Allelic polymorphisms at the H-2A and HLA-DQ loci influence the response of murine lymphocytes to the Mycoplasma arthritidis superantigen MAM. Infect Immun 1997; 65:4190-8. [PMID: 9317026 PMCID: PMC175602 DOI: 10.1128/iai.65.10.4190-4198.1997] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Mycoplasma arthritidis, an agent of rodent arthritis, produces a potent superantigen (SAg), MAM. Previous work established that MAM is presented to T cells by murine H-2E or the homologous human HLA-DR molecules and that lymphocytes lacking a functional H-2E molecule fail to respond to MAM. Recently, more potent and purified preparations of MAM of known protein content have become available. This enabled us to more effectively compare the response of MAM with that of other SAgs by using lymphocytes from mice whose cells express different H-2A and HLA-DQ molecules. Here we demonstrate that cells from some H-2E-negative mouse strains respond to higher concentrations of MAM. By use of inbred, congenic, and recombinant mice, we show that these differences are, in fact, exercised at the level of the major histocompatibility complex (MHC) and that allelic polymorphisms at H-2A influence reactivity to MAM. In addition, polymorphisms at HLA-DQ, the human homolog of H-2A, also influence responsiveness to MAM. Cells expressing DQw6 (HLA-DQA1*0103 and DQBI*0601 chains) gave much higher responses to MAM than did cells expressing DQw8 (DQA1*0301 and DQB1*0302 chains). In fact, responses of lymphocytes expressing DQB1*0601 chains homozygously were as high as those observed for cells expressing a functional H-2E molecule. Murine lymphocytes responded less well to staphylococcal enterotoxin B (SEB) and SEA, but mouse cells expressing human MHC molecules gave much higher responses. The patterns of reactivity observed with cells expressing the various murine and human alleles differed for MAM, SEB, and SEA, suggesting that each of these SAgs interacts with different regions or residues on MHC molecules. It has been hypothesized that SAgs might play a role in susceptibility to autoimmune disease. Allelic polymorphisms at MHC loci might therefore influence susceptibility to autoimmune disease by affecting immunoreactivity to specific superantigens.
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Affiliation(s)
- B C Cole
- Division of Rheumatology, University of Utah School of Medicine, Salt Lake City 84132, USA.
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