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Abstract
Trl 1 is an essential 827-amino-acid enzyme that executes the end-healing and end-sealing steps of tRNA splicing in Saccharomyces cerevisiae. Trl1 consists of two catalytic domains--an N-terminal adenylyltransferase/ligase component (amino acids 1-388) and a C-terminal 5'-kinase/cyclic phosphodiesterase component (amino acids 389-827)--that can function in tRNA splicing in vivo when expressed as separate polypeptides. Sedimentation analysis indicates that the ligase and kinase/CPD domains are monomeric proteins that do not form a stable complex in trans. To understand the structural requirements for the RNA ligase component, we performed a mutational analysis of amino acids that are conserved in Trl1 homologs from other fungi. Alanine scanning identified 23 new residues as essential for Trl1-(1-388) activity in vivo. Structure-activity relationships at these positions, and four essential residues defined previously, were clarified by introducing 50 different conservative substitutions. Lethal mutations of Lys114, Glu184, Glu266, and Lys284 abolished Trl1 adenylyltransferase activity in vitro. The essential elements embrace (1) putative equivalents of nucleotidyltransferase motifs I, Ia, III, IV, and V found in DNA ligases, T4 RNA ligase 2, and mRNA capping enzymes; (2) an N-terminal segment shared with the T4 RNA ligase 1 subfamily only; and (3) a constellation of conserved residues specific to fungal tRNA splicing enzymes. We identify yeastlike tRNA ligases in the proteomes of Leishmania and Trypanosoma. These findings recommend tRNA ligase as a target for antifungal and antiprotozoal drug discovery.
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Affiliation(s)
- Li Kai Wang
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10021, USA
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202
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Yon C, Teramoto T, Mueller N, Phelan J, Ganesh VK, Murthy KHM, Padmanabhan R. Modulation of the nucleoside triphosphatase/RNA helicase and 5'-RNA triphosphatase activities of Dengue virus type 2 nonstructural protein 3 (NS3) by interaction with NS5, the RNA-dependent RNA polymerase. J Biol Chem 2005; 280:27412-9. [PMID: 15917225 DOI: 10.1074/jbc.m501393200] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dengue virus type 2 (DEN2), a member of the Flaviviridae family, is a re-emerging human pathogen of global significance. DEN2 nonstructural protein 3 (NS3) has a serine protease domain (NS3-pro) and requires the hydrophilic domain of NS2B (NS2BH) for activation. NS3 is also an RNA-stimulated nucleoside triphosphatase (NTPase)/RNA helicase and a 5'-RNA triphosphatase (RTPase). In this study the first biochemical and kinetic properties of full-length NS3 (NS3FL)-associated NTPase, RTPase, and RNA helicase are presented. The NS3FL showed an enhanced RNA helicase activity compared with the NS3-pro-minus NS3, which was further enhanced by the presence of the NS2BH (NS2BH-NS3FL). An active protease catalytic triad is not required for the stimulatory effect, suggesting that the overall folding of the N-terminal protease domain contributes to this enhancement. In DEN2-infected mammalian cells, NS3 and NS5, the viral 5'-RNA methyltransferase/polymerase, exist as a complex. Therefore, the effect of NS5 on the NS3 NTPase activity was examined. The results show that NS5 stimulated the NS3 NTPase and RTPase activities. The NS5 stimulation of NS3 NTPase was dose-dependent until an equimolar ratio was reached. Moreover, the conserved motif, 184RKRK, of NS3 played a crucial role in binding to RNA substrate and modulating the NTPase/RNA helicase and RTPase activities of NS3.
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Affiliation(s)
- Changsuek Yon
- Department of Microbiology and Immunology, Georgetown University School of Medicine, Washington D. C. 20057, USA
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203
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Hausmann S, Zheng S, Fabrega C, Schneller SW, Lima CD, Shuman S. Encephalitozoon cuniculi mRNA cap (guanine N-7) methyltransferase: methyl acceptor specificity, inhibition BY S-adenosylmethionine analogs, and structure-guided mutational analysis. J Biol Chem 2005; 280:20404-12. [PMID: 15760890 DOI: 10.1074/jbc.m501073200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Encephalitozoon cuniculi mRNA cap (guanine N-7) methyltransferase Ecm1 has been characterized structurally but not biochemically. Here we show that purified Ecm1 is a monomeric protein that catalyzes methyl transfer from S-adenosylmethionine (AdoMet) to GTP. The reaction is cofactor-independent and optimal at pH 7.5. Ecm1 also methylates GpppA, GDP, and dGTP but not ATP, CTP, UTP, ITP, or m(7)GTP. The affinity of Ecm1 for the cap dinucleotide GpppA (K 0.1 mm) is higher than that for GTP (K(m) 1 mm) or GDP (K(m) 2.4 mm). Methylation of GTP by Ecm1 in the presence of 5 microm AdoMet is inhibited by the reaction product AdoHcy (IC(50) 4 microm) and by substrate analogs sinefungin (IC(50) 1.5 microm), aza-AdoMet (IC(50) 100 microm), and carbocyclic aza-AdoMet (IC(50) 35 microm). The crystal structure of an Ecm1.aza-AdoMet binary complex reveals that the inhibitor occupies the same site as AdoMet. Structure-function analysis of Ecm1 by alanine scanning and conservative substitutions identified functional groups necessary for methyltransferase activity in vivo. Amino acids Lys-54, Asp-70, Asp-78, and Asp-94, which comprise the AdoMet-binding site, and Phe-141, which contacts the cap guanosine, are essential for cap methyltransferase activity in vitro.
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Affiliation(s)
- Stéphane Hausmann
- Molecular Biology and Structural Biology Programs, Sloan-Kettering Institute, New York, New York 10021, USA
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204
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Broderick L, Yokota SJ, Reineke J, Mathiowitz E, Stewart CC, Barcos M, Kelleher RJ, Bankert RB. Human CD4+ effector memory T cells persisting in the microenvironment of lung cancer xenografts are activated by local delivery of IL-12 to proliferate, produce IFN-gamma, and eradicate tumor cells. THE JOURNAL OF IMMUNOLOGY 2005; 174:898-906. [PMID: 15634912 DOI: 10.4049/jimmunol.174.2.898] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The implantation of small pieces of human primary lung tumor biopsy tissue into SCID mice results in a viable s.c. xenograft in which the tissue architecture, including tumor-associated leukocytes, tumor cells, and stromal cells, is preserved in a functional state. By monitoring changes in tumor volume, gene expression patterns, cell depletion analysis, and the use of function-blocking Abs, we previously established in this xenograft model that exogenous IL-12 mobilizes human tumor-associated leukocytes to kill tumor cells in situ by indirect mechanisms that are dependent upon IFN-gamma. In this study immunohistochemistry and FACS characterize the early cellular events in the tumor microenvironment induced by IL-12. By 5 days post-IL-12 treatment, the constitutively present human CD45(+) leukocytes have expanded and infiltrated into tumor-rich areas of the xenograft. Two weeks post-treatment, there is expansion of the human leukocytes and complete effacement of the tumor compared with tumor progression and gradual loss of most human leukocytes in control-treated xenografts. Immunohistochemical analyses reveal that the responding human leukocytes are primarily activated or memory T cells, with smaller populations of B cells, macrophages, plasma cells, and plasmacytoid dendritic cells capable of producing IFN-alpha. The predominant cell population was also characterized by FACS and was shown to have a phenotype consistent with a CD4(+) effector memory T cell. We conclude that quiescent CD4(+) effector memory T cells are present within the tumor microenvironment of human lung tumors and can be reactivated by the local and sustained release of IL-12 to proliferate and secrete IFN-gamma, leading to tumor cell eradication.
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Affiliation(s)
- Lori Broderick
- Department of Microbiology and Immunology, State University of New York, Buffalo, NY 14214, USA
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205
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Changela A, Martins A, Shuman S, Mondragón A. Crystal structure of baculovirus RNA triphosphatase complexed with phosphate. J Biol Chem 2005; 280:17848-56. [PMID: 15713658 DOI: 10.1074/jbc.m500885200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Baculovirus RNA 5'-triphosphatase (BVP) exemplifies a family of RNA-specific cysteine phosphatases that includes the RNA triphosphatase domains of metazoan and plant mRNA capping enzymes. Here we report the crystal structure of BVP in a phosphate-bound state at 1.5 A resolution. BVP adopts the characteristic cysteine-phosphatase alpha/beta fold and binds two phosphate ions in the active site region, one of which is proposed to mimic the phosphate of the product complex after hydrolysis of the covalent phosphoenzyme intermediate. The crystal structure highlights the role of backbone amides and side chains of the P-loop motif (118)HCTHGXNRT(126) in binding the cleavable phosphate and stabilizing the transition state. Comparison of the BVP structure to the apoenzyme of mammalian RNA triphosphatase reveals a concerted movement of the Arg-125 side chain (to engage the phosphate directly) and closure of an associated surface loop over the phosphate in the active site. The structure highlights a direct catalytic role of Asn-124, which is the signature P-loop residue of the RNA triphosphatase family and a likely determinant of the specificity of BVP for hydrolysis of phosphoanhydride linkages.
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Affiliation(s)
- Anita Changela
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA
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206
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Dickmanns A, Ficner R. Role of the 5’-cap in the biogenesis of spliceosomal snRNPs. FINE-TUNING OF RNA FUNCTIONS BY MODIFICATION AND EDITING 2005. [DOI: 10.1007/b106799] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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207
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Williams MA, Bevan MJ. Shortening the infectious period does not alter expansion of CD8 T cells but diminishes their capacity to differentiate into memory cells. THE JOURNAL OF IMMUNOLOGY 2005; 173:6694-702. [PMID: 15557161 DOI: 10.4049/jimmunol.173.11.6694] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Following a primary immune response, a portion of effector T cells gives rise to long-lived memory cells. Although primary expansion and differentiation of effector CD8 T cells is dictated by a brief exposure to Ag, it is unclear whether full memory differentiation is also programmed within the same short window. By carefully modulating the kinetics of Listeria monocytogenes infection, we analyzed the requirements for the programming of effector and memory T cell development in vivo. We find that although limiting the infectious period to the first 24-48 h does not impact the size of the primary CD8 response, the ensuing memory population is significantly diminished. This effect is particularly pronounced in the development of tissue-homing memory cells and is inversely proportional to the initial infectious dose. In contrast to CD8 responses, the differentiation of primary CD4 responses was highly dependent on the continued presence of the infection. Shortening the duration of the infection greatly reduced the development of CD4 effector responses in the spleen and prevented their trafficking to peripheral sites of infection. We propose that the stimulus received by CD8 T cells during the early stages of infection largely contribute to the differentiation of CD8 effector cells, whereas continued or distinct signals received at later stages influence their ability to differentiate into memory cells.
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Affiliation(s)
- Matthew A Williams
- Department of Immunology and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA
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208
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Jansen VAA, Altes HK, Funk GA, Wodarz D. Contrasting B cell- and T cell-based protective vaccines. J Theor Biol 2004; 234:39-48. [PMID: 15721034 DOI: 10.1016/j.jtbi.2004.11.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2004] [Revised: 11/02/2004] [Accepted: 11/03/2004] [Indexed: 11/19/2022]
Abstract
A substantial research effort is devoted to the development of vaccines based on T cells. Such a vaccine would provide a means to protect against infection with HIV and stop the current pandemic. Here we investigate the possibility to develop a protective T cell-based vaccine. We do this by means of a mathematical model which describes the dynamics of a pathogen and the immune system in the early stages of infection. We compare an immune response that is near immediate--as is the case for a humoral response--with that of a response in which the effector cells have to be formed from precursor cells--as occurs in T cell responses. The latter applies to a T cell-based vaccine. A near immediate response is associated with a threshold number of effector cells above which an infection cannot take hold. For a T cell-based vaccine this threshold increases with the amount of antigen the immune system is exposed to. For small initial doses, as one would naturally expect to occur, this gives rise to impractically large thresholds. Thus, although a T cell vaccine might work against a high dose exposure, it might fail when exposed against to a low-dose exposure. This limits, we argue, the efficacy of T cell-based vaccines.
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Affiliation(s)
- Vincent A A Jansen
- School of Biological Sciences, Royal Holloway-University of London, Egham, Surrey TW20 0EX, UK.
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209
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Hausmann S, Altura MA, Witmer M, Singer SM, Elmendorf HG, Shuman S. Yeast-like mRNA capping apparatus in Giardia lamblia. J Biol Chem 2004; 280:12077-86. [PMID: 15556935 DOI: 10.1074/jbc.m412063200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
A scheme of eukaryotic phylogeny has been suggested based on the structure and physical linkage of the RNA triphosphatase and RNA guanylyltransferase enzymes that catalyze mRNA cap formation. Here we show that the unicellular pathogen Giardia lamblia encodes an mRNA capping apparatus consisting of separate triphosphatase and guanylyltransferase components, which we characterize biochemically. We also show that native Giardia mRNAs have blocked 5'-ends and that 7-methylguanosine caps promote translation of transfected mRNAs in Giardia in vivo. The Giardia triphosphatase belongs to the tunnel family of metal-dependent phosphohydrolases that includes the RNA triphosphatases of fungi, microsporidia, and protozoa such as Plasmodium and Trypanosoma. The tunnel enzymes adopt a unique active-site fold and are structurally and mechanistically unrelated to the cysteine-phosphatase-type RNA triphosphatases found in metazoans and plants, which comprise part of a bifunctional triphosphataseguanylyltransferase fusion protein. All available evidence now points to the separate tunnel-type triphosphatase and guanylyltransferase as the aboriginal state of the capping apparatus. We identify a putative tunnel-type triphosphatase and a separate guanylyltransferase encoded by the red alga Cyanidioschyzon merolae. These findings place fungi, protozoa, and red algae in a common lineage distinct from that of metazoa and plants.
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Affiliation(s)
- Stéphane Hausmann
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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210
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Wang XZ, Brehm MA, Welsh RM. Preapoptotic phenotype of viral epitope-specific CD8 T cells precludes memory development and is an intrinsic property of the epitope. THE JOURNAL OF IMMUNOLOGY 2004; 173:5138-47. [PMID: 15470058 DOI: 10.4049/jimmunol.173.8.5138] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Virus-specific CD8 T cells after clearance of infection reduce their number in lymphoid organs by apoptotic death and by migration into peripheral tissues. During and after infection, many lymphocytic choriomeningitis virus (LCMV)-specific CD8 T cells in lymphoid but not peripheral tissues are in a preapoptotic state, as detected by the early apoptosis marker annexin V. In this report, we investigated the significance of this preapoptotic state and how it may be influenced by viral epitope specificity. Stimulation with anti-CD3 or IL-2 in vitro postponed DNA fragmentation in annexin V+ cells, but adoptive transfer studies in vivo showed that this preapoptotic phenotype precluded the development of functional memory. CD8 T cells specific to LCMV epitopes NP396 and gp33 differed in their preapoptotic state, with NP396-specific T cells binding more annexin V than gp33-specific T cells. These epitope- and tissue-dependent differences were seen in primary, memory, and secondary responses and in mice receiving different displays of Ag by infection with LCMV strains of different tropisms or by infection with vaccinia virus recombinants expressing LCMV proteins. Thus, the epitope-dependent differences in apoptosis were independent of virus tropisms, duration of Ag exposure, and competition within APCs, and were an intrinsic property of the epitope. The tissue-dependent and epitope-dependent preapoptotic state correlated with reduced expression of IL-7Ralpha.
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Affiliation(s)
- Xiaoting Z Wang
- Program in Immunology and Virology, Department of Pathology, University of Massachusetts Medical School, Worcester 01655, USA
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211
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Corbin GA, Harty JT. Duration of Infection and Antigen Display Have Minimal Influence on the Kinetics of the CD4+T Cell Response toListeria monocytogenesInfection. THE JOURNAL OF IMMUNOLOGY 2004; 173:5679-87. [PMID: 15494519 DOI: 10.4049/jimmunol.173.9.5679] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The T cell response to infection consists of clonal expansion of effector cells, followed by contraction to memory levels. It was previously thought that the duration of infection determines the magnitude and kinetics of the T cell response. However, recent analysis revealed that transition between the expansion and contraction phases of the Ag-specific CD8+ T cell response is not affected by experimental manipulation in the duration of infection or Ag display. We studied whether the duration of infection and Ag display influenced the kinetics of the Ag-specific CD4+ T cell response to Listeria monocytogenes (LM) infection. We found that truncating infection and Ag display with antibiotic treatment as early as 24 h postinfection had minimal impact on the expansion or contraction of CD4+ T cells; however, the magnitudes of the Ag-specific CD4+ and CD8+ T cell responses were differentially affected by the timing of antibiotic treatment. Treatment of LM-infected mice with antibiotics at 24 h postinfection did not prevent generation of detectable CD4+ and CD8+ memory T cells at 28 days after infection, vigorous secondary expansion of these memory T cells, or protection against a subsequent LM challenge. These results demonstrate that events within the first few days of infection stimulate CD4+ and CD8+ T cell responses that are capable of carrying out the full program of expansion and contraction to functional memory, independently of prolonged infection or Ag display.
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Affiliation(s)
- Gail A Corbin
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
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212
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Obar JJ, Crist SG, Leung EK, Usherwood EJ. IL-15-independent proliferative renewal of memory CD8+ T cells in latent gammaherpesvirus infection. THE JOURNAL OF IMMUNOLOGY 2004; 173:2705-14. [PMID: 15294989 DOI: 10.4049/jimmunol.173.4.2705] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
IL-15 is known to be critical in the homeostasis of Ag-specific memory CD8(+) T cells following acute viral infection. However, little is known about the homeostatic requirements of memory CD8(+) T cells during a latent viral infection. We have used the murine gammaherpesvirus-68 (MHV-68) model system to investigate whether IL-15 is necessary for the maintenance of memory CD8(+) T cells during a latent viral infection. IL-15 is not essential either for the initial control of MHV-68 infection or for the maintenance of MHV-68-specific memory CD8(+) T cells. Even at 140 days postinfection, the proportion of CD8(+) T cells recognizing the MHV-68 epitopes were the same as in control mice. The maintenance of these memory CD8(+) T cells was attributable to their ability to turn over in vivo, probably in response to the presence of low levels of Ag. IL-15(-/-) mice had a significantly higher turnover rate within the virus-specific memory CD8(+) T cell population, which was the result of increased levels of viral gene expression rather than an increase in viral load. These cells did not accumulate in the spleens of the IL-15(-/-) mice due to an increased sensitivity to apoptosis as a result of decreased Bcl-2 levels. Intriguingly, memory CD8(+) T cells from latently infected mice failed to undergo homeostatic proliferation in a naive secondary host. These data highlight fundamental differences between memory CD8(+) T cells engaged in active immune surveillance of latent viral infections vs memory CD8(+) T cells found after acute viral infections.
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Affiliation(s)
- Joshua J Obar
- Department of Microbiology and Immunology, Dartmouth Medical School, Lebanon, NH 03756, USA
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213
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Montfort MJ, Bouwer HGA, Wagner CR, Hinrichs DJ. The Development of Functional CD8 T Cell Memory afterListeria monocytogenesInfection Is Not Dependent on CD40. THE JOURNAL OF IMMUNOLOGY 2004; 173:4084-90. [PMID: 15356158 DOI: 10.4049/jimmunol.173.6.4084] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The immunologic requirements for generating long-lived protective CD8 T cell memory remain unclear. Memory CD8 populations generated in the absence of CD4 Th cells reportedly have functional defects, and at least a subset of CD8 T cells transiently express CD40 after activation, suggesting that direct CD4-CD8 T cell interactions through CD40 may influence the magnitude and functional quality of memory CD8 populations. To ascertain the role of CD40 in such direct T cell interactions, we investigated CD8 T cell responses in CD40-/- mice after infection with Listeria monocytogenes, an intracellular bacterium that induces APC activation and thus priming of CD8 T cells independently of CD4 Th cell help through CD40. In this study we show that memory CD8 T cells generated in CD40-deficient mice show in vivo cytotoxicity and cytokine production equivalent to CD8 memory T cells from wild-type mice. Upon secondary Listeria infection, CD40-/- memory CD8 T cells expand to greater numbers than seen in wild-type mice. These results indicate that CD40 ligation on CD8 T cells, although reportedly a part of CD8 T cell memory development in an H-Y-directed response, is not needed for the development of functional memory CD8 T cell populations after Listeria infection.
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Affiliation(s)
- Megan J Montfort
- Department of Molecular Microbiology, Oregon Health and Science University, Portland 97239, USA
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214
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Robbins SH, Tessmer MS, Mikayama T, Brossay L. Expansion and contraction of the NK cell compartment in response to murine cytomegalovirus infection. THE JOURNAL OF IMMUNOLOGY 2004; 173:259-66. [PMID: 15210783 DOI: 10.4049/jimmunol.173.1.259] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
NK cells are capable of responding quickly to infectious challenge and contribute to the early defense against a wide variety of pathogens. Although the innate NK cell response to murine CMV (MCMV) has been extensively characterized, its resolution and the fate of the activated NK cell population remains unexplored. Herein, we characterize both the expansion and contraction phases of the NK cell response to MCMV. We demonstrate that NK cell recruitment into the immune response to MCMV infection is restricted to the first 3 days of infection and as the peripheral NK cell compartment expands, NK cells undergo accelerated phenotypic maturation. During the resolution of the immune response, NK cell compartmental contraction is marked by the selective death of responding NK cells. Additionally, throughout the infection, a naive NK cell pool that remains responsive to additional stimuli is actively maintained. These findings illustrate the plasticity of the NK cell compartment in response to pathogens and underscore the homeostatic maintenance of the resting peripheral NK cell pool.
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Affiliation(s)
- Scott H Robbins
- Department of Molecular Microbiology and Immunology and Graduate Program in Pathobiology, Division of Biology and Medicine, Brown University, Providence, RI 02912, USA
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215
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Boissonnas A, Combadiere C, Lavergne E, Maho M, Blanc C, Debré P, Combadiere B. Antigen distribution drives programmed antitumor CD8 cell migration and determines its efficiency. THE JOURNAL OF IMMUNOLOGY 2004; 173:222-9. [PMID: 15210778 DOI: 10.4049/jimmunol.173.1.222] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Understanding both the role of tumor Ag in CD8 cell differentiation and the reasons that CD8 cells may work inefficiently is crucial for therapeutic approaches in cancer. We studied OT-1 CD8 cell responses in vivo in a differential Ag-distribution model that used EG-7, the EL-4 thymoma transfected with OVA. On their initial Ag encounter, OT-1 CD8 cells underwent programmed expansion in the lymph nodes, where they acquired the ability to migrate to the encapsulated tumor site after > or =4 divisions, without continuous antigenic stimulation. This short antigenic stimulation was sufficient to induce the migration differentiation program, which included modulation of chemokine receptor mRNA expression and down-regulation of CD62L. Moreover, Ag quantity determined the behavior of the OT-1 CD8 cells, including their effector functions and sensitivity to apoptosis. Thus, the initial Ag encounter drives the programmed cell migration potencies, but neither effector functions nor cell death can occur without continuous TCR triggering.
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Affiliation(s)
- Alexandre Boissonnas
- Laboratoire d'Immunologie Cellulaire, Institut National de la Santé et de la Recherche Médicale, Unité 543, Faculté de Médecine Pitié-Salpêtrière, 91 Boulevard de l'Hôpital, 75634 Paris cedex 13, France
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216
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Matsutani S. Similarities in transcription factor IIIC subunits that bind to the posterior regions of internal promoters for RNA polymerase III. BMC Evol Biol 2004; 4:26. [PMID: 15298704 PMCID: PMC514540 DOI: 10.1186/1471-2148-4-26] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2004] [Accepted: 08/09/2004] [Indexed: 12/12/2022] Open
Abstract
Background In eukaryotes, RNA polymerase III (RNAP III) transcribes the genes for small RNAs like tRNAs, 5S rRNA, and several viral RNAs, and short interspersed repetitive elements (SINEs). The genes for these RNAs and SINEs have internal promoters that consist of two regions. These two regions are called the A and B blocks. The multisubunit transcription factor TFIIIC is required for transcription initiation of RNAP III; in transcription of tRNAs, the B-block binding subunit of TFIIIC recognizes a promoter. Although internal promoter sequences are conserved in eukaryotes, no evidence of homology between the B-block binding subunits of vertebrates and yeasts has been reported previously. Results Here, I reported the results of PSI-BLAST searches using the B-block binding subunits of human and Shizosacchromyces pombe as queries, showing that the same Arabidopsis proteins were hit with low E-values in both searches. Comparison of the convergent iterative alignments obtained by these PSI-BLAST searches revealed that the vertebrate, yeast, and Arabidopsis proteins have similarities in their N-terminal one-third regions. In these regions, there were three domains with conserved sequence similarities, one located in the N-terminal end region. The N-terminal end region of the B-block binding subunit of Saccharomyces cerevisiae is tentatively identified as a HMG box, which is the DNA binding motif. Although I compared the alignment of the N-terminal end regions of the B-block binding subunits, and their homologs, with that of the HMG boxes, it is not clear whether they are related. Conclusion Molecular phylogenetic analyses using the small subunit rRNA and ubiquitous proteins like actin and α-tubulin, show that fungi are more closely related to animals than either is to plants. Interestingly, the results obtained in this study show that, with respect to the B-block binding subunits of TFIIICs, animals appear to be evolutionarily closer to plants than to fungi.
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Affiliation(s)
- Sachiko Matsutani
- Division of Microbiology, National Institute of Health Sciences, Setagaya-ku, Tokyo 158-8501, Japan.
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217
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Haining WN, Anderson DG, Little SR, von Bergwelt-Baildon MS, Cardoso AA, Alves P, Kosmatopoulos K, Nadler LM, Langer R, Kohane DS, von Berwelt-Baildon MS. pH-Triggered Microparticles for Peptide Vaccination. THE JOURNAL OF IMMUNOLOGY 2004; 173:2578-85. [PMID: 15294974 DOI: 10.4049/jimmunol.173.4.2578] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Improving vaccine delivery to human APCs is a way to increase the CTL response to vaccines. We report the use of a novel pH-triggered microparticle that exploits the ability of APCs to cross-present MHC I-restricted Ags that have been engulfed in the low pH environment of the phagosome. A model MHC class I-restricted peptide Ag from the influenza A matrix protein was encapsulated in spray-dried microparticles composed of dipalmitoylphosphatidylcholine and the pH-sensitive polymethacrylate Eudragit E100. Release of the peptide from the particle was triggered by a drop in pH to the acidity normally found in the phagosome. The particles were efficiently phagocytosed by human monocytes and dendritic cells with minimal cellular toxicity and no functional impairment. Encapsulation of the peptide in the microparticles resulted in efficient presentation of the peptide to CD8(+) T cells by human dendritic cells in vitro, and was superior to unencapsulated peptide or peptide encapsulated in an analogous pH-insensitive particle. Vaccination of human HLA-A*0201 transgenic mice with peptide encapsulated in pH-triggering microparticles resulted in priming of CTL responses. These microparticles can be modified to coencapsulate a range of adjuvants along with the Ag of interest. Encapsulation of MHC I epitopes in pH-triggered microparticles increases Ag presentation and may improve CD8(+) T cell priming to peptide vaccines against viruses and cancer.
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Affiliation(s)
- W Nicholas Haining
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, and Division of Pediatric Hematology/Oncology, Children's Hospital, Boston, MA 02115, USA
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218
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Fuller MJ, Khanolkar A, Tebo AE, Zajac AJ. Maintenance, loss, and resurgence of T cell responses during acute, protracted, and chronic viral infections. THE JOURNAL OF IMMUNOLOGY 2004; 172:4204-14. [PMID: 15034033 DOI: 10.4049/jimmunol.172.7.4204] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The acute phase of many viral infections is associated with the induction of a pronounced CD8 T cell response which plays a principle role in clearing the infection. By contrast, certain infections are not as readily controlled. In this study, we have used the well-defined system of lymphocytic choriomeningitis virus (LCMV) infection of mice to determine quantitative and qualitative changes in virus-specific CD8 T cell responses that rapidly resolve acute infections, more slowly control protracted infections, or fail to clear chronic infections. Acute LCMV infection elicits potent, functional, multi-epitope-specific CD8 T cell responses. Virus-specific CD8 T cells also expand, albeit to a lesser extent, during protracted LCMV infection. Under these conditions, there is a progressive diminution in the capacity to produce IL-2, TNF-alpha, and IFN-gamma. Changes in cytotoxic activities are also detectable but differ depending upon the specificity of the responding cells. As the infection is slowly resolved, a resurgence of cytokine production by virus-specific CD8 T cells is observed. CD4-deficient mice cannot control infection with certain strains of LCMV, but do mount multi-epitope-specific CD8 T cell responses that also lose effector capabilities; however, they are not maintained indefinitely in an unresponsive state as these cells become deleted over time. Overall, our findings suggest that constant high viral loads result in the progressive diminution of T cell effector functions and subsequent physical loss of the responding cells, whereas if the viral load is brought under control a partial restoration of CD8 T cell functions can occur.
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Affiliation(s)
- Michael J Fuller
- Department of Microbiology, University of Alabama, Birmingham, AL 35294, USA
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219
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Marzo AL, Vezys V, Klonowski KD, Lee SJ, Muralimohan G, Moore M, Tough DF, Lefrançois L. Fully Functional Memory CD8 T Cells in the Absence of CD4 T Cells. THE JOURNAL OF IMMUNOLOGY 2004; 173:969-75. [PMID: 15240684 DOI: 10.4049/jimmunol.173.2.969] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The role of CD4 T cells in providing help to CD8 T cells in primary and secondary responses to infection remains controversial. Using recombinant strains of virus and bacteria expressing the same Ag, we determined the requirement for CD4 T cells in endogenous CD8 T cell responses to infection with vesicular stomatitis virus and Listeria monocytogenes (LM). Depletion of CD4 T cells had no effect on the frequency of primary or secondary vesicular stomatitis virus-specific CD8 T cells in either lymphoid or nonlymphoid tissues. In contrast, the primary LM-specific CD8 T cell response was CD4 T cell dependent. Surprisingly, the LM-specific CD8 T cell recall response was also CD4 T cell dependent, which correlated with a requirement for CD40/CD40L interactions. However, concomitant inhibition of CD40L and CD4 T cell removal revealed that these pathways may be operating independently. Importantly, despite the absence of CD4 T cells during the recall response or throughout the entire response, CD8 memory T cells were functional effectors and proliferated equivalently to their "helped" counterparts. These data call into question the contention that CD4 T cells condition memory CD8 T cells during the primary response and indicate that the principal role of CD4 T cells in generating CD8 memory cells after infection is augmentation of proliferation or survival through costimulatory signals.
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Affiliation(s)
- Amanda L Marzo
- Division of Immunology, University of Connecticut Health Center, Farmington, CT 06030, USA
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220
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Wong P, Pamer EG. Disparate in vitro and in vivo requirements for IL-2 during antigen-independent CD8 T cell expansion. THE JOURNAL OF IMMUNOLOGY 2004; 172:2171-6. [PMID: 14764683 DOI: 10.4049/jimmunol.172.4.2171] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Transient TCR stimulation induces multiple rounds of CD8 T cell division without further requirement for Ag. The mechanism driving Ag-independent proliferation, however, remains unclear. In this study, we show that the initial duration of TCR stimulation positively correlates with the number of divisions that CD8 T cells subsequently undergo. We find that increased periods of Ag stimulation result in enhanced CD25 up-regulation and greater IL-2 production by CD8 T cells. Depletion of IL-2 from T cell cultures with specific Abs dramatically impairs programmed proliferation. Consistent with this result, IL-2-deficient T cells undergo markedly attenuated Ag-independent proliferation in vitro. Although IL-2 production by stimulated CD8 T cells appears to be essential for in vitro proliferation, upon transfer into recipient mice, IL-2-deficient CD8 T cells undergo extensive proliferation in vivo after transient stimulation. Furthermore, the extent of in vivo proliferation correlates with the duration of in vitro Ag stimulation. These results indicate that the requirements for autocrine IL-2 production by CD8 T cells differs between in vitro and in vivo conditions and suggests that factors in addition to IL-2 can support Ag-independent CD8 T cell proliferation.
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Affiliation(s)
- Phillip Wong
- Department of Medicine, Immunology Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
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221
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Carrio R, Bathe OF, Malek TR. Initial Antigen Encounter Programs CD8+T Cells Competent to Develop into Memory Cells That Are Activated in an Antigen-Free, IL-7- and IL-15-Rich Environment. THE JOURNAL OF IMMUNOLOGY 2004; 172:7315-23. [PMID: 15187107 DOI: 10.4049/jimmunol.172.12.7315] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Although much is known concerning the immunobiology of CD8+ T memory cells, the initial events favoring the generation of CD8+ T memory cells remain poorly defined. Using a culture system that yields memory-like CD8+ T cells, we show that 1 day after Ag encounter, Ag-activated T cells developed into memory-like T cells, but this optimally occurred 3 days after Ag encounter. Key phenotypic, functional, and molecular properties that typify central memory T cells were expressed within 48 h when the activated CD8+ T cells were cultured with IL-7 or IL-15 in the absence of Ag or following transfer into normal mice. These data support a model whereby Ag activation of naive CD8+ T cells not only programs effector cell expansion and contraction but the potential to develop into a memory cell which ensues in an Ag-free environment containing IL-7 or IL-15.
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Affiliation(s)
- Roberto Carrio
- Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, FL 33101, USA
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222
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Accapezzato D, Francavilla V, Paroli M, Casciaro M, Chircu LV, Cividini A, Abrignani S, Mondelli MU, Barnaba V. Hepatic expansion of a virus-specific regulatory CD8(+) T cell population in chronic hepatitis C virus infection. J Clin Invest 2004. [PMID: 15057302 DOI: 10.1172/jci200420515] [Citation(s) in RCA: 242] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Regulatory T (T(R)) cells consist of phenotypically and functionally distinct CD4(+) and CD8(+) T cell subsets engaged both in maintaining self-tolerance and in preventing anti-non-self effector responses (microbial, tumor, transplant, and so on) that may be harmful to the host. Here we propose that the proinflammatory function of virus-specific memory effector CCR7(-)CD8(+) T cells, which are massively recruited in the liver, are inefficient (in terms of IFN-gamma production) in patients with chronic hepatitis C virus (HCV) infection because of the concomitant presence of virus-specific CCR7(-)CD8(+) T(R) cells producing considerable amounts of IL-10. These CD8(+) T(R) cells are antigen specific, as they can be stimulated by HCV epitopes and suppress T cell responses that are in turn restored by the addition of neutralizing anti-IL-10. This study provides for the first time to our knowledge direct evidence of the existence of virus-specific CD8(+) T(R) cells that infiltrate the livers of patients with chronic HCV infection, identifies IL-10 as a soluble inhibitory factor mediating suppression, and suggests that these cells play a pivotal role in controlling hepatic effector CD8(+) T cell responses.
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Affiliation(s)
- Daniele Accapezzato
- Fondazione Andrea Cesalpino, Dipartimento di Medicina Interna, Università degli Studi di Roma La Sapienza, Rome, Italy
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223
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Gamadia LE, van Leeuwen EMM, Remmerswaal EBM, Yong SL, Surachno S, Wertheim-van Dillen PME, Ten Berge IJM, Van Lier RAW. The Size and Phenotype of Virus-Specific T Cell Populations Is Determined by Repetitive Antigenic Stimulation and Environmental Cytokines. THE JOURNAL OF IMMUNOLOGY 2004; 172:6107-14. [PMID: 15128796 DOI: 10.4049/jimmunol.172.10.6107] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Based on the expression of the TNFR SFP CD27, two Ag-primed CD8(+) T cell subsets can be discerned in the circulation of healthy individuals: CD27(+) T cells that produce a variety of cytokines but do not display immediate cytolytic activity; and cytotoxic CD27(-) T cells, which secrete only IFN-gamma and TNF-alpha. The mechanism that controls the generation of these different phenotypes is unknown. We show that CMV reactivation not only increases the number of virus-specific T cells but also induces their transition from a CD27(+) to a CD27(-) phenotype. In support of a relation between pool size and phenotype in a cohort of latently infected individuals, the number of Ag-specific CD27(-) CD8(+) T cells was found to be linearly related to the total number of CMV-specific CD8(+) T cells. In vitro studies revealed that the acquisition of the CD27(-) phenotype on CMV-specific T cells depended on the interaction of CD27 with its cellular ligand, CD70. Expression of CD70 was proportional to the amount of antigenic stimulation and blocked by the CD4(+) T cell-derived cytokine IL-21. Thus, induction of CD70, which may vary in distinct viral infections, appears to be a key factor in determining the size and phenotype of the CMV-specific T cell population in latently infected individuals.
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Affiliation(s)
- Laila E Gamadia
- Renal Transplant Unit, Department of Internal Medicine, Laboratory for Experimental Immunology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
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224
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Matsutani S. Question of the Animal-Plant-Fungal Divergence. GENOMICS, PROTEOMICS & BIOINFORMATICS 2004; 2:69. [PMID: 15629045 PMCID: PMC5172444 DOI: 10.1016/s1672-0229(04)02011-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Sachiko Matsutani
- Division of Microbiology, National Institute of Health Sciences, Japan.
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225
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Ha SJ, Kim DJ, Baek KH, Yun YD, Sung YC. IL-23 induces stronger sustained CTL and Th1 immune responses than IL-12 in hepatitis C virus envelope protein 2 DNA immunization. THE JOURNAL OF IMMUNOLOGY 2004; 172:525-31. [PMID: 14688363 DOI: 10.4049/jimmunol.172.1.525] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
IL-23 is a heterodimeric cytokine consisting of p19 and the p40 subunit of IL-12. IL-23 has been shown to possess IL-12-like biological activities, but is different in its capacity to stimulate memory T cells in vitro. In this study, we investigated whether IL-23 could influence envelope protein 2 (E2)-specific cell-mediated immunity induced by immunization of hepatitis C virus E2 DNA. We found that IL-23 induced long-lasting Th1 and CTL immune responses to E2, which are much stronger than IL-12-mediated immune responses. Interestingly, IL-23N220L, an N-glycosylation mutant showing reduced expression of excess p40 without changing the level of IL-23, exhibited a higher ratio of IFN-gamma- to IL-4-producing CD4(+) T cell frequency than did wild-type IL-23, suggesting a negative regulatory effect of p40 on Th1-prone immune response induced by IL-23. These data suggest that IL-23, particularly IL-23N220L, would be an effective adjuvant of DNA vaccine for the induction of durable Ag-specific T cell immunity.
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MESH Headings
- Adjuvants, Immunologic/administration & dosage
- Adjuvants, Immunologic/genetics
- Adjuvants, Immunologic/therapeutic use
- Amino Acid Sequence
- Animals
- Cytotoxicity, Immunologic/genetics
- Female
- Genetic Vectors
- Hepacivirus/genetics
- Hepacivirus/immunology
- Humans
- Immunity, Cellular/genetics
- Injections, Intramuscular
- Interleukin-12/administration & dosage
- Interleukin-12/genetics
- Interleukin-12/therapeutic use
- Interleukin-12 Subunit p40
- Interleukin-23
- Interleukin-23 Subunit p19
- Interleukins/administration & dosage
- Interleukins/genetics
- Interleukins/therapeutic use
- Mice
- Mice, Inbred BALB C
- Molecular Sequence Data
- Protein Subunits/administration & dosage
- T-Lymphocytes, Cytotoxic/immunology
- T-Lymphocytes, Cytotoxic/virology
- Th1 Cells/immunology
- Th1 Cells/virology
- Vaccines, DNA/administration & dosage
- Vaccines, DNA/genetics
- Vaccines, DNA/immunology
- Viral Envelope Proteins/administration & dosage
- Viral Envelope Proteins/genetics
- Viral Envelope Proteins/immunology
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Affiliation(s)
- Sang-Jun Ha
- National Research Laboratory of DNA Medicine, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-gu, Pohang 790-784, Republic of Korea
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226
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Fabrega C, Hausmann S, Shen V, Shuman S, Lima CD. Structure and mechanism of mRNA cap (guanine-N7) methyltransferase. Mol Cell 2004; 13:77-89. [PMID: 14731396 DOI: 10.1016/s1097-2765(03)00522-7] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A suite of crystal structures is reported for a cellular mRNA cap (guanine-N7) methyltransferase in complex with AdoMet, AdoHcy, and the cap guanylate. Superposition of ligand complexes suggests an in-line mechanism of methyl transfer, albeit without direct contacts between the enzyme and either the N7 atom of guanine (the attacking nucleophile), the methyl carbon of AdoMet, or the sulfur of AdoMet/AdoHcy (the leaving group). The structures indicate that catalysis of cap N7 methylation is accomplished by optimizing proximity and orientation of the substrates, assisted by a favorable electrostatic environment. The enzyme-ligand structures, together with new mutational data, fully account for the biochemical specificity of the cap guanine-N7 methylation reaction, an essential and defining step of eukaryotic mRNA synthesis.
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Affiliation(s)
- Carme Fabrega
- Biochemistry Department, Structural Biology Program, Weill Medical College, Cornell University, New York, NY 10021, USA
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227
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Huang YL, Han YT, Chang YT, Hsu YH, Meng M. Critical residues for GTP methylation and formation of the covalent m7GMP-enzyme intermediate in the capping enzyme domain of bamboo mosaic virus. J Virol 2004; 78:1271-80. [PMID: 14722282 PMCID: PMC321370 DOI: 10.1128/jvi.78.3.1271-1280.2004] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Open reading frame 1 of Bamboo mosaic virus (BaMV), a Potexvirus in the alphavirus-like superfamily, encodes a 155-kDa replicase responsible for the formation of the 5' cap structure and replication of the viral RNA genome. The N-terminal domain of the viral replicase functions as an mRNA capping enzyme, which exhibits both GTP methyltransferase and S-adenosylmethionine (AdoMet)-dependent guanylyltransferase activities. We mutated each of the four conserved amino acids among the capping enzymes of members within alphavirus-like superfamily and a dozen of other residues to gain insight into the structure-function relationship of the viral enzyme. The mutant enzymes were purified and subsequently characterized. H68A, the mutant enzyme bearing a substitution at the conserved histidine residue, has an approximately 10-fold increase in GTP methyltransferase activity but completely loses the ability to form the covalent m(7)GMP-enzyme intermediate. High-pressure liquid chromatography analysis confirmed the production of m(7)GTP by the GTP methyltransferase activity of H68A. Furthermore, the produced m(7)GTP sustained the formation of the m(7)GMP-enzyme intermediate for the wild-type enzyme in the presence of S-adenosylhomocysteine (AdoHcy), suggesting that the previously observed AdoMet-dependent guanylation of the enzyme using GTP results from reactions of GTP methylation and subsequently guanylation of the enzyme using m(7)GTP. Mutations occurred at the other three conserved residues (D122, R125, and Y213), and H66 resulted in abolition of activities for both GTP methylation and formation of the covalent m(7)GMP-enzyme intermediate. Mutations of amino acids such as K121, C234, D310, W312, R316, K344, W406, and K409 decreased both activities by various degrees, and the extents of mutational effects follow similar trends. The affinity to AdoMet of the various BaMV capping enzymes, except H68A, was found in good correlations with not only the magnitude of GTP methyltransferase activity but also the capability of forming the m(7)GMP-enzyme intermediate. Taken together with the AdoHcy dependence of guanylation of the enzyme using m(7)GTP, a basic working mechanism, with the contents of critical roles played by the binding of AdoMet/AdoHcy, of the BaMV capping enzyme is proposed and discussed.
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Affiliation(s)
- Yih-Leh Huang
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227, Republic of China
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228
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Khanolkar A, Fuller MJ, Zajac AJ. CD4 T Cell-Dependent CD8 T Cell Maturation. THE JOURNAL OF IMMUNOLOGY 2004; 172:2834-44. [PMID: 14978084 DOI: 10.4049/jimmunol.172.5.2834] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have investigated the contribution of CD4 T cells to the optimal priming of functionally robust memory CD8 T cell subsets. Intranasal infection of CD4 T cell-deficient (CD4(-/-)) mice with lymphocytic choriomeningitis virus resulted in the elaboration of virus-specific CD8 T cell responses that cleared the infection. However, by comparison with normal mice, the virus-specific CD8 T cells in CD4(-/-) mice were quantitatively and qualitatively different. In normal mice, lymphocytic choriomeningitis virus-specific memory CD8 T cells are CD44(high), many are CD122(high), and a majority of these cells regain expression of CD62L overtime. These cells produce IFN-gamma and TNF-alpha, and a subset also produces IL-2. In the absence of CD4 T cell help, a distinct subset of memory CD8 T cells develops that remains CD62L(low) up to 1 year after infection and exhibits a CD44(int)CD122(low) phenotype. These cells are qualitatively different from their counterparts in normal hosts, as their capacity to produce TNF-alpha and IL-2 is diminished. In addition, although CD4-independent CD8 T cells can contain the infection following secondary viral challenge, their ability to expand is impaired. These findings suggest that CD4 T cell responses not only contribute to the optimal priming of CD8 T cells in chronically infected hosts, but are also critical for the phenotypic and functional maturation of CD8 T cell responses to Ags that are more rapidly cleared. Moreover, these data imply that the development of CD62L(high) central memory CD8 T cells is arrested in the absence of CD4 T cell help.
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Affiliation(s)
- Aaruni Khanolkar
- Department of Microbiology, University of Alabama, Birmingham, AL 35294, USA
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229
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Chang J, Cho JH, Lee SW, Choi SY, Ha SJ, Sung YC. IL-12 Priming during In Vitro Antigenic Stimulation Changes Properties of CD8 T Cells and Increases Generation of Effector and Memory Cells. THE JOURNAL OF IMMUNOLOGY 2004; 172:2818-26. [PMID: 14978082 DOI: 10.4049/jimmunol.172.5.2818] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Antigenic and costimulatory signals trigger a developmental program by which naive CD8 T cells differentiate into effector and memory cells. However, initial cytokine signals that regulate the generation of effector and memory CD8 T cells are not well understood. In this study, we show that IL-12 priming during in vitro antigenic stimulation results in the significant increase of both primary and memory CD8 T cell population in mice after adoptive transfer of activated cells. The effect of IL-12 priming is closely associated with qualitative changes in CD8 T cells, such as reduced MHC I tetramer binding and CD69 expression, altered distribution of lipid rafts, decreased cytolytic activity, and less susceptibility to apoptosis. Furthermore, exogenous IL-12 priming improved the intrinsic survival properties of memory CD8 T cells, leading to better protective immunity and vaccine-induced memory CD8 T cell responses. However, the experiments with IL-12p40- and IL-12Rbeta1-deficient mice showed similar levels of primary and memory CD8 T cell responses compared with wild-type mice, implying that endogenous IL-12 and/or IL-12R signaling in vivo is not critical for CD8 T cell immunity. Together, our results suggest that IL-12 can serve as an important, but dispensable regulatory factor for the development of CD8 T cells, and IL-12 priming could be useful in many medical applications.
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Affiliation(s)
- Jun Chang
- Division of Molecular and Life Science, National Laboratory of DNA Medicine, Pohang University of Science and Technology, Hyoja-Dong, Pohang, Kyungbuk, Republic of Korea
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230
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Tewari K, Sacha J, Gao X, Suresh M. Effect of chronic viral infection on epitope selection, cytokine production, and surface phenotype of CD8 T cells and the role of IFN-gamma receptor in immune regulation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2004; 172:1491-500. [PMID: 14734726 DOI: 10.4049/jimmunol.172.3.1491] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Regulation of CD8 T cell responses in chronic viral infections is not well understood. In this study, we have compared the CD8 T cell responses to immunodominant and subdominant epitopes during an acute and a chronic lymphocytic choriomeningitis virus (LCMV) infection in mice. The epitope hierarchy of the primary CD8 T cell response was similar in acute and chronic LCMV infections. However, strikingly, the epitope hierarchy of the primary CD8 T cell response was conserved in the T cell memory only in an acute but not in a chronic LCMV infection. Interestingly, in an acute infection, increasing the viral dose caused significant changes in the epitope hierarchy of the LCMV-specific memory CD8 T cell pool, with no effect on the primary CD8 T cell response. Functional and phenotypic analyses revealed that exposure of CD8 T cells to extended periods of antigenic stimulation could lead to long-term defects in cytokine production and alteration in expression of cell surface L-selectin (CD62L). Whereas expression of CD44 was minimally altered, a greater proportion of LCMV-specific memory CD8 T cells were CD62L(low) in mice that have recovered from a chronic LCMV infection, compared with acutely infected mice. Mechanistic studies showed that IFN-gammaR deficiency altered the epitope hierarchy of the pool of LCMV-specific memory CD8 T cells without significantly affecting the immunodominance of the primary CD8 T cell response in an acute infection. Taken together, these findings should further our understanding about the regulation of T cell responses in human chronic viral infections.
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Affiliation(s)
- Kavita Tewari
- Department of Pathobiological Sciences, University of Wisconsin, Madison, WI 53706
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231
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Boonman ZFHM, van Mierlo GJD, Fransen MF, Franken KLMC, Offringa R, Melief CJM, Jager MJ, Toes REM. Intraocular Tumor Antigen Drains Specifically to Submandibular Lymph Nodes, Resulting in an Abortive Cytotoxic T Cell Reaction. THE JOURNAL OF IMMUNOLOGY 2004; 172:1567-74. [PMID: 14734736 DOI: 10.4049/jimmunol.172.3.1567] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ocular immune privilege is considered essential in the protection against sight-threatening immune responses, as illustrated by the ability of the ocular environment to permit the growth of tumors that are rejected when implanted at other sites. Although several studies indicate that soluble Ag can drain directly into the spleen when injected into the anterior chamber, the primary site of intraocular tumor Ag presentation to tumor-specific CTLs has not been studied. To gain a better understanding of the mechanism involved in ocular immune privilege, we examined to which lymphoid organs anterior chamber tumor Ags primarily drain. Our data show that intraocular tumor Ag drains exclusively to the submandibular lymph nodes, resulting in activation of tumor-specific CTLs, whereas no Ag drainage was found in spleen. However, these tumor-specific CTLs do not distribute systemically and, as a consequence, intraocular tumor growth is unhampered. A similar lack of CTL efficacy has been observed in mice bearing s.c. tumors, which is converted to a systemic tumoricidal CTL response by administration of agonistic anti-CD40 mAb. In contrast, systemic anti-CD40 treatment of eye tumor-bearing mice did not result in mobilizing tumor-specific CTLs or tumor eradication. Together, these results show that intraocular tumor Ag drains to regional lymph nodes for activation of tumor-specific CTLs. However, the induced tumor-specific immunity is insufficient for tumor clearance, even combined with otherwise highly effective immune intervention protocols.
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MESH Headings
- Adenovirus E1A Proteins/biosynthesis
- Adenovirus E1A Proteins/genetics
- Adenovirus E1A Proteins/immunology
- Adenoviruses, Human/genetics
- Adenoviruses, Human/immunology
- Animals
- Anterior Chamber/immunology
- Anterior Chamber/pathology
- Anterior Chamber/virology
- Antigens, Neoplasm/genetics
- Antigens, Neoplasm/immunology
- CD40 Antigens/physiology
- Cell Division/genetics
- Cell Division/immunology
- Cell Line, Tumor
- Cell Movement/genetics
- Cell Movement/immunology
- Cytotoxicity, Immunologic/genetics
- Epitopes, T-Lymphocyte/immunology
- Eye Neoplasms/immunology
- Eye Neoplasms/pathology
- Eye Neoplasms/virology
- Graft Rejection/immunology
- Graft Rejection/pathology
- Graft Rejection/virology
- Lymph Nodes/immunology
- Lymph Nodes/pathology
- Lymph Nodes/virology
- Lymphocyte Activation/genetics
- Lymphocyte Activation/immunology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Skin Neoplasms/immunology
- Skin Neoplasms/pathology
- Skin Neoplasms/virology
- Submandibular Gland/immunology
- Submandibular Gland/pathology
- Submandibular Gland/virology
- T-Lymphocytes, Cytotoxic/immunology
- T-Lymphocytes, Cytotoxic/metabolism
- T-Lymphocytes, Cytotoxic/virology
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Affiliation(s)
- Zita F H M Boonman
- Department of Ophthalmology, Leiden University Medical Center, Leiden, The Netherlands
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232
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Messingham KAN, Badovinac VP, Harty JT. Deficient anti-listerial immunity in the absence of perforin can be restored by increasing memory CD8+ T cell numbers. THE JOURNAL OF IMMUNOLOGY 2004; 171:4254-62. [PMID: 14530349 DOI: 10.4049/jimmunol.171.8.4254] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Compared with wild-type (WT) mice, Listeria monocytogenes (LM)-vaccinated perforin-deficient (PKO) mice have elevated levels of CD8(+) T cell memory, but exhibit reduced levels of protection against virulent LM. In this study, Ag-specific CD8(+) T cells from LM-vaccinated WT and PKO mice were used in adoptive transfer assays to determine the contribution of perforin-dependent cytolysis in protective immunity to LM. Perforin deficiency resulted in an approximately 5-fold reduction in the per-cell protective capacity of Ag-specific memory CD8(+) T cells that was not caused by differences in memory cell quality as measured by CD62L/CD27 expression, TCR repertoire use, functional avidity, differences in expansion of Ag-specific cells upon infection, or maintenance of memory levels over time. However, perforin-deficient CD8(+) T cells exhibited reduced in vivo cytotoxic function compared to WT CD8(+) T cells. Consistent with the existence of perforin-independent effector pathways, double-vaccinated PKO mice were as resistant to challenge with LM as single-vaccinated WT mice. Thus, increasing the number of memory CD8(+) T cells can overcome diminished per-cell protective immunity in the absence of perforin.
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233
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De Boer RJ, Homann D, Perelson AS. Different dynamics of CD4+ and CD8+ T cell responses during and after acute lymphocytic choriomeningitis virus infection. THE JOURNAL OF IMMUNOLOGY 2004; 171:3928-35. [PMID: 14530309 DOI: 10.4049/jimmunol.171.8.3928] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We fit a mathematical model to data characterizing the primary cellular immune response to lymphocytic choriomeningitis virus. The data enumerate the specific CD8(+) T cell response to six MHC class I-restricted epitopes and the specific CD4(+) T cell responses to two MHC class II-restricted epitopes. The peak of the response occurs around day 8 for CD8(+) T cells and around day 9 for CD4(+) T cells. By fitting a model to the data, we characterize the kinetic differences between CD4(+) and CD8(+) T cell responses and among the immunodominant and subdominant responses to the various epitopes. CD8(+) T cell responses have faster kinetics in almost every aspect of the response. For CD8(+) and CD4(+) T cells, the doubling time during the initial expansion phase is 8 and 11 h, respectively. The half-life during the contraction phase following the peak of the response is 41 h and 3 days, respectively. CD4(+) responses are even slower because their contraction phase appears to be biphasic, approaching a 35-day half-life 8 days after the peak of the response. The half-life during the memory phase is 500 days for the CD4(+) T cell responses and appears to be lifelong for the six CD8(+) T cell responses. Comparing the responses between the various epitopes, we find that immunodominant responses have an earlier and/or larger recruitment of precursors cells before the expansion phase and/or have a faster proliferation rate during the expansion phase.
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Affiliation(s)
- Rob J De Boer
- Theoretical Biology, Utrecht University, Utrecht, The Netherlands.
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234
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Bertram EM, Dawicki W, Sedgmen B, Bramson JL, Lynch DH, Watts TH. A Switch in Costimulation from CD28 to 4-1BB during Primary versus Secondary CD8 T Cell Response to Influenza In Vivo. THE JOURNAL OF IMMUNOLOGY 2004; 172:981-8. [PMID: 14707071 DOI: 10.4049/jimmunol.172.2.981] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
4-1BBL(-/-) mice exhibit normal primary CD8 T cell responses to influenza virus, but show decreased CD8 T cell numbers late in the primary response as well as decreased secondary responses. In contrast, CD28(-/-) mice are defective in initial CD8 T cell expansion. Using agonistic anti-4-1BB Ab to replace the CD28 or 4-1BB signal, we examined the timing of the required signals for CD28 vs 4-1BB costimulation. A single dose of agonistic anti-4-1BB Ab added only during priming restores the secondary CD8 T cell response in CD28(-/-) mice. Once the T cell numbers in the primary response reach a minimum threshold, a full secondary response is achieved even in the absence of CD28. In contrast, anti-4-1BB added during priming fails to correct the defective secondary response in 4-1BBL(-/-) mice, whereas addition of anti-4-1BB during challenge fully restores this response. Thus, there is a switch in costimulatory requirement from CD28 to 4-1BB during primary vs recall responses. Adoptive transfer studies show that T cells primed in 4-1BBL(-/-) or wild-type mice are equally capable of re-expansion when rechallenged in wild-type mice. These studies rule out a model in which signals delivered through 4-1BB during priming program the T cells to give a full recall response and suggest that 4-1BB-4-1BBL interactions take place at later stages in the immune response. The results indicate that anti-4-1BB or 4-1BBL therapy will be most effective during the boost phase of a prime-boost vaccination strategy.
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MESH Headings
- 4-1BB Ligand
- Animals
- Antibodies, Viral/biosynthesis
- Antigens, CD
- CD28 Antigens/genetics
- CD28 Antigens/physiology
- CD4-Positive T-Lymphocytes/immunology
- CD4-Positive T-Lymphocytes/virology
- CD8-Positive T-Lymphocytes/immunology
- CD8-Positive T-Lymphocytes/metabolism
- CD8-Positive T-Lymphocytes/virology
- Immune Sera/administration & dosage
- Immune Sera/physiology
- Immunization, Secondary/methods
- Immunologic Memory/genetics
- Influenza A virus/immunology
- Influenza Vaccines/administration & dosage
- Influenza Vaccines/immunology
- Injections, Intraperitoneal
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Orthomyxoviridae Infections/genetics
- Orthomyxoviridae Infections/immunology
- Receptors, Nerve Growth Factor/deficiency
- Receptors, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/immunology
- Receptors, Nerve Growth Factor/physiology
- Receptors, Tumor Necrosis Factor/deficiency
- Receptors, Tumor Necrosis Factor/genetics
- Receptors, Tumor Necrosis Factor/immunology
- Receptors, Tumor Necrosis Factor/physiology
- Tumor Necrosis Factor Receptor Superfamily, Member 9
- Tumor Necrosis Factor-alpha/deficiency
- Tumor Necrosis Factor-alpha/genetics
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Affiliation(s)
- Edward M Bertram
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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235
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Na D, Park I, Lee KH, Lee D. Integration of Immune Models Using Petri Nets. LECTURE NOTES IN COMPUTER SCIENCE 2004. [DOI: 10.1007/978-3-540-30220-9_17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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236
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Gong C, Martins A, Shuman S. Structure-Function Analysis of Trypanosoma brucei RNA Triphosphatase and Evidence for a Two-metal Mechanism. J Biol Chem 2003; 278:50843-52. [PMID: 14525979 DOI: 10.1074/jbc.m309188200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Trypanosoma brucei RNA triphosphatase TbCet1 is a 252-amino acid polypeptide that catalyzes the first step in mRNA cap formation. By performing an alanine scan of TbCet1, we identified six amino acids that are essential for triphosphatase activity (Glu-52, Arg-127, Glu-168, Arg-186, Glu-216, and Glu-218). These results consolidate the proposal that protozoan, fungal, and Chlorella virus RNA triphosphatases belong to a single family of metal-dependent NTP phosphohydrolases with a unique tunnel active site composed of eight beta strands. Limited proteolysis of TbCet1 suggests that the hydrophilic N terminus is surface-exposed, whereas the catalytic core domain is tightly folded with the exception of a protease-sensitive loop (76WKGRRARKT84) between two of the putative tunnel strands. The catalytic domain of TbCet1 is extraordinarily thermostable. It remains active after heating for 2 h at 75 degrees C. Analysis by zonal velocity sedimentation indicates that TbCet1 is a monomeric enzyme, unlike fungal RNA triphosphatases, which are homodimers. We show that tripolyphosphate is a potent competitive inhibitor of TbCet1 (Ki 1.4 microm) that binds more avidly to the active site than the ATP substrate (Km 25 microm). We present evidence of synergistic activation of the TbCet1 triphosphatase by manganese and magnesium, consistent with a two-metal mechanism of catalysis. Our findings provide new insight to the similarities (in active site tertiary structure and catalytic mechanism) and differences (in quaternary structure and thermal stability) among the different branches of the tunnel enzyme family.
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Affiliation(s)
- Chunling Gong
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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237
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Sawaya R, Schwer B, Shuman S. Genetic and biochemical analysis of the functional domains of yeast tRNA ligase. J Biol Chem 2003; 278:43928-38. [PMID: 12933796 DOI: 10.1074/jbc.m307839200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Yeast tRNA ligase (Trl1) converts cleaved tRNA half-molecules into spliced tRNAs containing a 2'-PO4, 3'-5' phosphodiester at the splice junction. Trl1 performs three reactions: (i) the 2',3'-cyclic phosphate of the proximal fragment is hydrolyzed to a 3'-OH, 2'-PO4 by a cyclic phosphodiesterase (CPD); (ii) the 5'-OH of the distal fragment is phosphorylated by an NTP-dependent polynucleotide kinase; and (iii) the 3'-OH, 2'-PO4, and 5'-PO4 ends are sealed by an ATP-dependent RNA ligase. Trl1 consists of an N-terminal adenylyltransferase domain that resembles T4 RNA ligase 1, a central domain that resembles T4 polynucleotide kinase, and a C-terminal CPD domain that resembles the 2H phosphotransferase enzyme superfamily. Here we show that all three domains are essential in vivo, although they need not be linked in the same polypeptide. We identify five amino acids in the adenylyltransferase domain (Lys114, Glu266, Gly267, Lys284, and Lys286) that are essential for Trl1 activity and are located within motifs I (114KANG117), IV (266EGFVI270), and V (282FFKIK286) that comprise the active sites of DNA ligases, RNA capping enzymes, and T4 RNA ligases 1 and 2. Mutations K404A and T405A in the P-loop (401GXGKT405) of the central kinase-like domain had no effect on Trl1 function in vivo. The K404A and T405A mutations eliminated ATP-dependent kinase activity but preserved GTP-dependent kinase activity. A double alanine mutant in the P-loop was lethal in vivo and abolished GTP-dependent kinase activity. These results suggest that GTP is the physiological substrate and that the Trl1 kinase has a single NTP binding site of which the P-loop is a component. Two other mutations in the central domain were lethal in vivo and either abolished (D425A) or severely reduced (R511A) GTP-dependent RNA kinase activity in vitro. Mutations of the signature histidines of the CPD domain were either lethal (H777A) or conferred a ts growth phenotype (H673A).
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Affiliation(s)
- Rana Sawaya
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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238
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Lefrançois L, Marzo A, Williams K. Sustained response initiation is required for T cell clonal expansion but not for effector or memory development in vivo. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:2832-9. [PMID: 12960304 DOI: 10.4049/jimmunol.171.6.2832] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The factors determining whether an immune response is productive are poorly understood. To understand the circumstances affecting the early stage of the immune response which determine whether memory is generated, the CD8 T cell response was mapped in detail following immunization with live or heat-killed bacteria. Our results demonstrate that even in response to a weak immunogen, functional memory cell development is linked to effector cell induction in lymphoid and nonlymphoid tissues. The main defect in the response to killed microorganisms is inefficient induction of clonal expansion. This failure is due to a contracted, but costimulation-dependent activation phase in the lymphoid tissues, resulting in rapid but abortive growth. Conversely, the response to live bacteria is characterized by protracted early T cell sequestration in lymphoid tissues. Thus, memory development requires effector induction, while optimal clonal expansion is regulated by the duration of response initiation.
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Affiliation(s)
- Leo Lefrançois
- Department of Medicine, Division of Immunology, University of Connecticut Health Center, Farmington, CT 06030, USA.
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239
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Abstract
Retrotransposons have proliferated extensively in eukaryotic lineages; the genomes of many animals and plants comprise 50% or more retrotransposon sequences by weight. There are several persuasive arguments that the enzymatic lynchpin of retrotransposon replication, reverse transcriptase (RT), is an ancient enzyme. Moreover, the direct progenitors of retrotransposons are thought to be mobile self-splicing introns that actively propagate themselves via reverse transcription, the group II introns, also known as retrointrons. Retrointrons are represented in modern genomes in very modest numbers, and thus far, only in certain eubacterial and organellar genomes. Archaeal genomes are nearly devoid of RT in any form. In this study, I propose a model to explain this unusual distribution, and rationalize it with the proposed ancient origin of the RT gene. A cap and tail hypothesis is proposed. By this hypothesis, the specialized terminal structures of eukaryotic mRNA provide the ideal molecular environment for the lengthening, evolution, and subsequent massive expansion of highly mobile retrotransposons, leading directly to the retrotransposon-cluttered structure that typifies modern metazoan genomes and the eventual emergence of retroviruses.
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Affiliation(s)
- Jef D Boeke
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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240
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Maris CH, Miller JD, Altman JD, Jacob J. A transgenic mouse model genetically tags all activated CD8 T cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:2393-401. [PMID: 12928386 DOI: 10.4049/jimmunol.171.5.2393] [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: 01/06/2023]
Abstract
Identifying and characterizing Ag-specific CD8+ T cells are central to the study of immunological memory. Although powerful strategies such as MHC tetramers and peptide-induced cytokine production assays exist for identifying Ag-specific CD8+ T cells, alternate strategies that are not dependent upon a priori knowledge of the immunodominant and subdominant antigenic epitopes, as well as the MHC background of the animal are of obvious utility. In this study, we present a transgenic mouse model that uses Cre-loxP recombination to permanently mark all activated CD8+ T cells with beta-galactosidase. We used the lymphocytic choriomeningitis virus infection model to track the dynamics of the antiviral CD8+ T cell responses. We show that in this transgenic mouse model system, all of the antiviral effector and memory CD8+ T cells are contained within the beta-gal-marked CD8+ T cell population.
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Affiliation(s)
- Charles H Maris
- Department of Microbiology and Immunology, Emory Vaccine Center, Emory University, Atlanta, GA 30329, USA
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241
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Abstract
CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.
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Affiliation(s)
- Phillip Wong
- Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
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242
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Abstract
In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.
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Affiliation(s)
- Daniel C Douek
- Human Immunology Section Vaccine Research Center, NIAID, NIH, Bethesda, Maryland 20892, USA.
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243
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Hausmann S, Pei Y, Shuman S. Homodimeric quaternary structure is required for the in vivo function and thermal stability of Saccharomyces cerevisiae and Schizosaccharomyces pombe RNA triphosphatases. J Biol Chem 2003; 278:30487-96. [PMID: 12788946 DOI: 10.1074/jbc.m303060200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Saccharomyces cerevisiae Cet1 and Schizosaccharomyces pombe Pct1 are the essential RNA triphosphatase components of the mRNA capping apparatus of budding and fission yeast, respectively. Cet1 and Pct1 share a baroque active site architecture and a homodimeric quaternary structure. The active site is located within a topologically closed hydrophilic beta-barrel (the triphosphate tunnel) that rests on a globular core domain (the pedestal) composed of elements from both protomers of the homodimer. Earlier studies of the effects of alanine cluster mutations at the crystallographic dimer interface of Cet1 suggested that homodimerization is important for triphosphatase function in vivo, albeit not for catalysis. Here, we studied the effects of 14 single-alanine mutations on Cet1 activity and thereby pinpointed Asp280 as a critical side chain required for dimer formation. We find that disruption of the dimer interface is lethal in vivo and renders Cet1 activity thermolabile at physiological temperatures in vitro. In addition, we identify individual residues within the pedestal domain (Ile470, Leu519, Ile520, Phe523, Leu524, and Ile530) that stabilize Cet1 in vivo and in vitro. In the case of Pct1, we show that dimerization depends on the peptide segment 41VPKIEMNFLN50 located immediately prior to the start of the Pct1 catalytic domain. Deletion of this peptide converts Pct1 into a catalytically active monomer that is defective in vivo in S. pombe and hypersensitive to thermal inactivation in vitro. Our findings suggest an explanation for the conservation of quaternary structure in fungal RNA triphosphatases, whereby the delicate tunnel architecture of the active site is stabilized by the homodimeric pedestal domain.
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Affiliation(s)
- Stéphane Hausmann
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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244
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Berenzon D, Schwenk RJ, Letellier L, Guebre-Xabier M, Williams J, Krzych U. Protracted protection to Plasmodium berghei malaria is linked to functionally and phenotypically heterogeneous liver memory CD8+ T cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:2024-34. [PMID: 12902507 DOI: 10.4049/jimmunol.171.4.2024] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We previously demonstrated that protection induced by radiation-attenuated (gamma) Plasmodium berghei sporozoites is linked to MHC class I-restricted CD8(+) T cells specific for exoerythrocytic-stage Ags, and that activated intrahepatic memory CD8(+) T cells are associated with protracted protection. In this study, we further investigated intrahepatic memory CD8(+) T cells to elucidate mechanisms required for their maintenance. Using phenotypic markers indicative of activation (CD44, CD45RB), migration (CD62L), and IFN-gamma production, we identified two subsets of intrahepatic memory CD8(+) T cells: the CD44(high)CD45RB(low)CD62L(low)CD122(low) phenotype, representing the dominant effector memory set, and the CD44(high)CD45RB(high)CD62L(low/high)CD122(high) phenotype, representing the central memory set. Only the effector memory CD8(+) T cells responded swiftly to sporozoite challenge by producing sustained IFN-gamma; the central memory T cells responded with delay, and the IFN-gamma reactivity was short-lived. In addition, the subsets of liver memory CD8(+) T cells segregated according to the expression of CD122 (IL-15R) in that only the central memory CD8(+) T cells were CD122(high), whereas the effector memory CD8(+) T cells were CD122(low). Moreover, the effector memory CD8(+) T cells declined as protection waned in mice treated with primaquine, a drug that interferes with the formation of liver-stage Ags. We propose that protracted protection induced by P. berghei radiation-attenuated sporozoites depends in part on a network of interactive liver memory CD8(+) T cell subsets, each representing a different phase of activation or differentiation, and the balance of which is profoundly affected by the repository of liver-stage Ag and IL-15.
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Affiliation(s)
- Dmitri Berenzon
- Department of Immunology and Entomology, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA
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245
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Hafalla JCR, Morrot A, Sano GI, Milon G, Lafaille JJ, Zavala F. Early self-regulatory mechanisms control the magnitude of CD8+ T cell responses against liver stages of murine malaria. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:964-70. [PMID: 12847268 DOI: 10.4049/jimmunol.171.2.964] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Following immunization with Plasmodium yoelii sporozoites, the CD8(+) T cell population specific for the SYVPSAEQI epitope expressed in sporozoite and liver stages of this malaria parasite revealed the existence of a short term Ag presentation process that translated into a single clonal burst. Further expansion of this CD8(+) T cell population in conditions of sustained Ag exposure and additional supply of naive cells was inhibited by regulatory mechanisms that were developed as early as 24-48 h after priming. Studies using mouse models for Plasmodium or influenza virus infections revealed that this mechanism is Ag specific and is mediated by activated CD8(+) T cells that inhibit the priming of naive cells. This interference of the priming of naive cells appeared to result from limited access to Ag-presenting dendritic cells, which become disabled or are eliminated after contact with activated cells. Thus, concomitantly with the development of their effector antimicrobial capacity, CD8(+) T cells also acquire a self-regulatory role that is likely to represent one of the earliest mechanisms induced in the course of an immune response and that limits the magnitude of the early expansion of CD8(+) T lymphocytes reactive to microorganisms.
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MESH Headings
- Animals
- Antigen-Presenting Cells/immunology
- Antigen-Presenting Cells/metabolism
- Antigens, Protozoan/administration & dosage
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- CD8-Positive T-Lymphocytes/cytology
- CD8-Positive T-Lymphocytes/immunology
- CD8-Positive T-Lymphocytes/parasitology
- CD8-Positive T-Lymphocytes/transplantation
- Cell Communication/immunology
- Cell Division/immunology
- Clone Cells
- Down-Regulation/immunology
- Interphase/immunology
- Liver Diseases, Parasitic/immunology
- Liver Diseases, Parasitic/parasitology
- Lymphocyte Activation/immunology
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Mice, Transgenic
- Plasmodium yoelii/growth & development
- Plasmodium yoelii/immunology
- Protozoan Proteins/administration & dosage
- Protozoan Proteins/genetics
- Protozoan Proteins/immunology
- Spleen/cytology
- Spleen/immunology
- Spleen/transplantation
- Sporozoites/growth & development
- Sporozoites/immunology
- T-Lymphocytes, Regulatory/cytology
- T-Lymphocytes, Regulatory/immunology
- T-Lymphocytes, Regulatory/parasitology
- T-Lymphocytes, Regulatory/transplantation
- Vaccination
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Affiliation(s)
- Julius C R Hafalla
- Department of Medical and Molecular Parasitology, New York University School of Medicine, New York, NY 10010, USA
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246
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Sawaya R, Shuman S. Mutational analysis of the guanylyltransferase component of Mammalian mRNA capping enzyme. Biochemistry 2003; 42:8240-9. [PMID: 12846573 DOI: 10.1021/bi034396d] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
RNA guanylyltransferase is an essential enzyme that catalyzes the second of three steps in the synthesis of the 5'-cap structure of eukaryotic mRNA. Here we conducted a mutational analysis of the guanylyltransferase domain of the mouse capping enzyme Mce1. We introduced 50 different mutations at 22 individual amino acids and assessed their effects on Mce1 function in vivo in yeast. We identified 16 amino acids as being essential for Mce1 activity (Arg299, Arg315, Asp343, Glu345, Tyr362, Asp363, Arg380, Asp438, Gly439, Lys458, Lys460, Asp468, Arg530, Asp532, Lys533, and Asn537) and clarified structure-activity relationships by testing the effects of conservative substitutions. The new mutational data for Mce1, together with prior mutational studies of Saccharomyces cerevisiae guanylyltransferase and the crystal structures of Chlorella virus and Candida albicans guanylyltransferases, provide a coherent picture of the functional groups that comprise and stabilize the active site. Our results extend and consolidate the hypothesis of a shared structural basis for catalysis by RNA capping enzymes, DNA ligases, and RNA ligases, which comprise a superfamily of covalent nucleotidyl transferases defined by a constellation of conserved motifs. Analysis of the effects of motif VI mutations on Mce1 guanylyltransferase activity in vitro highlights essential roles for Arg530, Asp532, Lys533, and Asn537 in GTP binding and nucleotidyl transfer.
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Affiliation(s)
- Rana Sawaya
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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247
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Peacock CD, Kim SK, Welsh RM. Attrition of virus-specific memory CD8+ T cells during reconstitution of lymphopenic environments. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:655-63. [PMID: 12847230 DOI: 10.4049/jimmunol.171.2.655] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Viruses can cause a severe lymphopenia early in infection and a subsequent, lasting loss of pre-existing CD8(+) memory T cells. We therefore questioned how well virus Ag-specific memory CD8(+) T cells could reconstitute mice rendered lymphopenic as a consequence of genetics, irradiation, or viral or poly(I:C)-induced cytokines. In each case, reconstitution of the CD8(+) compartment was associated with limited division of virus-specific memory T cells and a reduction in their proportion. This indicates that foreign Ag-experienced CD44(high)CD8(+) memory T cells may respond differently to homeostatic signals than other CD44(high)CD8(+) cells, and that events inducing lymphopenia may lead to a permanent reduction in T cell memory.
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Affiliation(s)
- Craig D Peacock
- Department of Pathology, University of Massachusetts Medical Center, Worcester, MA 01655, USA
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de Saint Basile G, Fischer A. Defective cytotoxic granule-mediated cell death pathway impairs T lymphocyte homeostasis. Curr Opin Rheumatol 2003; 15:436-45. [PMID: 12819472 DOI: 10.1097/00002281-200307000-00011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Hemophagocytic syndrome is a severe and often fatal syndrome resulting from excessive activation and proliferation of T lymphocytes and macrophages. Onset of a hemophagocytic syndrome characterized the course of several human inherited immune disorders, all of them resulting from molecular defects of the perforin-dependent cytotoxic process exerted by both T and Natural Killer (NK) lymphocytes. These disorders highlight the determinant role of this lytic pathway in the control of lymphocyte expansion and homeostasis. New effectors of this secretory pathway have been thus identified.
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Badovinac VP, Messingham KAN, Hamilton SE, Harty JT. Regulation of CD8+ T cells undergoing primary and secondary responses to infection in the same host. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 170:4933-42. [PMID: 12734336 DOI: 10.4049/jimmunol.170.10.4933] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Naive Ag-specific CD8(+) T cells expand, contract, and become memory cells after infection and/or vaccination. Memory CD8(+) T cells provide faster, more effective secondary responses against repeated exposure to the same pathogen. Using an adoptive transfer system with low numbers of trackable nontransgenic memory CD8(+) T cells, we showed that secondary responses can be comprised of both primary (naive) and secondary (memory) CD8(+) T cells after bacterial (Listeria monocytogenes) and/or viral (lymphocytic choriomeningitis virus) infections. The level of memory CD8(+) T cells present at the time of infection inversely correlated with the magnitude of primary CD8(+) T cell responses against the same epitope but directly correlated with the level of protection against infection. However, similar numbers of Ag-specific CD8(+) T cells were found 8 days postinfection no matter how many memory cells were present at the time of infection. Rapid contraction of primary CD8(+) T cell responses was not influenced by the presence of memory CD8(+) T cells. However, contraction of secondary CD8(+) T cell responses was markedly prolonged compared with primary responses in the same host mice. This situation occurred in response to lymphocytic choriomeningitis virus or L. monocytogenes infection and for CD8(+) T cell responses against multiple epitopes. The delayed contraction of secondary CD8(+) T cells was also observed after immunization with peptide-coated dendritic cells. Together, the results show that the level of memory CD8(+) T cells influences protective immunity and activation of naive precursors specific for the same epitope but has little impact on the magnitude or program of the CD8(+) T cell response.
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Abstract
The RNA triphosphatase component of vaccinia virus mRNA capping enzyme (the product of the viral D1 gene) belongs to a family of metal-dependent phosphohydrolases that includes the RNA triphosphatases of fungi, protozoa, Chlorella virus, and baculoviruses. The family is defined by two glutamate-containing motifs (A and C) that form the metal-binding site. Most of the family members resemble the fungal and Chlorella virus enzymes, which have a complex active site located within the hydrophilic interior of a topologically closed eight-stranded beta barrel (the so-called "triphosphate tunnel"). Here we queried whether vaccinia virus capping enzyme is a member of the tunnel subfamily, via mutational mapping of amino acids required for vaccinia triphosphatase activity. We identified four new essential side chains in vaccinia D1 via alanine scanning and illuminated structure-activity relationships by conservative substitutions. Our results, together with previous mutational data, highlight a constellation of six acidic and three basic amino acids that likely compose the vaccinia triphosphatase active site (Glu37, Glu39, Arg77, Lys107, Glu126, Asp159, Lys161, Glu192, and Glu194). These nine essential residues are conserved in all vertebrate and invertebrate poxvirus RNA capping enzymes. We discerned no pattern of clustering of the catalytic residues of the poxvirus triphosphatase that would suggest structural similarity to the tunnel proteins (exclusive of motifs A and C). We infer that the poxvirus triphosphatases are a distinct lineage within the metal-dependent RNA triphosphatase family. Their unique active site, which is completely different from that of the host cell's capping enzyme, recommends the poxvirus RNA triphosphatase as a molecular target for antipoxviral drug discovery.
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Affiliation(s)
- Chunling Gong
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10021, USA
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