组织蛋白酶S在抗原提呈过程中的作用

效应T细胞激活需要两个或以上的信号诱导.抗原肽结合MHC-Ⅱ分子的溶酶体途径（第一信号）包括两个重要的步骤：不变链（invariant chain Ii）降解和抗原加工.目前所知的溶酶体蛋白酶中,组织蛋白酶S（cathepsin S,cat S）被认为以非冗长的作用参与了上述两步过程,其还参与了降解细胞外基质（extracellular matrix,ECM）的过程.因此被认为在调节免疫、自身免疫性疾病、抗肿瘤免疫、组织重塑等方面是具有潜力的研究靶点.     

The Cell Biology of Antigen Processing

Abstract

T lymphocytes recognize antigen only after a series of intracellular events known as antigen processing. The result of antigen processing is the production of short segments of the primary peptide sequence bound to a polypeptide-binding groove on major histo compatibility complex (MHC) molecules. Antigen originates from one of two sites: intracellular or extra cellular. There are two corresponding pathways for antigen processing and two corresponding classes of MHC molecule. Analysis of each pathway has demonstrated that their separation is not purely anatomical, but is maintained by molecular interactions with other molecules. Antigen processing has been shown to regulate the overall immune response, but the mechanisms involved remain obscure.     

Virus-Mediated Suppression of the Antigen Presentation Molecule MR1

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Multiple Structural and Epigenetic Defects in the Human Leukocyte Antigen Class I Antigen Presentation Pathway in a Recurrent Metastatic Melanoma Following Immunotherapy

Scant information is available about the molecular basis of multiple HLA class I antigen-processing machinery defects in malignant cells, although this information contributes to our understanding of the molecular immunoescape mechanisms utilized by tumor cells and may suggest strategies to counteract them. In the present study we reveal a combination of IFN-γ-irreversible structural and epigenetic defects in HLA class I antigen-processing machinery in a recurrent melanoma metastasis after immunotherapy. These defects include loss of tapasin and one HLA haplotype as well as selective silencing of HLA-A3 gene responsiveness to IFN-γ. Tapasin loss is caused by a germ-line frameshift mutation in exon 3 (TAPBP^684delA) along with a somatic loss of the other gene copy. Selective silencing of HLA-A3 gene and its IFN-γ responsiveness is associated with promoter CpG methylation nearby site-α and TATA box, reversible after DNA methyltransferase 1 depletion. This treatment combined with tapasin reconstitution and IFN-γ stimulation restored the highest level of HLA class I expression and its ability to elicit cytotoxic T cell responses. These results represent a novel tumor immune evasion mechanism through impairing multiple components at various levels in the HLA class I antigen presentation pathway. These findings may suggest a rational design of combinatorial cancer immunotherapy harnessing DNA demethylation and IFN-γ response.     

MHC Class I Presentation of an Exogenous Polypeptide Antigen Encoded by the Murine AIDS Defective Virus

Peptides derived from endogenous proteins are presented by MHC class I molecules, whereas those derived from exogenous proteins are presented by MHC class II molecules. This strict segregation has been reconsidered in recent reports in which exogenous antigens are shown to be presented by MHC class I molecules in the phagocytic pathway. In this report, the presentation pathway of an exogenously added highly antigenic polypeptide encoded by the murine AIDS (MAIDS) defective virus gag p12 gene is investigated. A 25-mer polypeptide (P12–25) encoded within the gag p12 region of the MAIDS defective virus was found to be effective in stimulating unprimed B6 (H-2^b) CD8⁺ T cells in vitro. The presentation of P12–25 is sensitive to cytochalasin B and D, brefeldin A and gelonin, a ribosome-inactivating protein synthesis inhibitor, but less sensitive or resistant to lactacystin, a highly specific inhibitor of the proteasome. Interestingly, CA-074, a selective inhibitor of cathepsin B, inhibited presentation of the polypeptide, indicating its involvement in the degradation of the P12–25 polypeptide. In fact, when P12–25 was digested with purified cathepsin B in vitro, a highly antigenic 11-mer peptide containing the class I (H-2D^b)-binding motif was obtained. Our results favor the phagosome/macropinosome-to-cytosol-to-endoplasmic reticulum (ER)-to-cell surface pathway for exogenous antigens presented by MHC class I molecules. These findings may be relevant to exploiting peptide vaccines that specifically elicit CD8⁺ T cell immunity in vivo.     

Endoplasmic Reticulum Glycoprotein Quality Control Regulates CD1d Assembly and CD1d-mediated Antigen Presentation

The non-classical major histocompatibility complex (MHC) homologue CD1d presents lipid antigens to innate-like lymphocytes called natural-killer T (NKT) cells. These cells, by virtue of their broad cytokine repertoire, shape innate and adaptive immune responses. Here, we have assessed the role of endoplasmic reticulum glycoprotein quality control in CD1d assembly and function, specifically the role of a key component of the quality control machinery, the enzyme UDP glucose glycoprotein glucosyltransferase (UGT1). We observe that in UGT1-deficient cells, CD1d associates prematurely with β₂-microglobulin (β₂m) and is able to rapidly exit the endoplasmic reticulum. At least some of these CD1d-β₂m heterodimers are shorter-lived and can be rescued by provision of a defined exogenous antigen, α-galactosylceramide. Importantly, we show that in UGT1-deficient cells the CD1d-β₂m heterodimers have altered antigenicity despite the fact that their cell surface levels are unchanged. We propose that UGT1 serves as a quality control checkpoint during CD1d assembly and further suggest that UGT1-mediated quality control can shape the lipid repertoire of newly synthesized CD1d. The quality control process may play a role in ensuring stability of exported CD1d-β₂m complexes, in facilitating presentation of low abundance high affinity antigens, or in preventing deleterious responses to self lipids.     

An Evolutionary Analysis of Antigen Processing and Presentation across Different Timescales Reveals Pervasive Selection

The antigenic repertoire presented by MHC molecules is generated by the antigen processing and presentation (APP) pathway. We analyzed the evolutionary history of 45 genes involved in APP at the inter- and intra-species level. Results showed that 11 genes evolved adaptively in mammals. Several positively selected sites involve positions of fundamental importance to the protein function (e.g. the TAP1 peptide-binding domains, the sugar binding interface of langerin, and the CD1D trafficking signal region). In CYBB, all selected sites cluster in two loops protruding into the endosomal lumen; analysis of missense mutations responsible for chronic granulomatous disease (CGD) showed the action of different selective forces on the very same gene region, as most CGD substitutions involve aminoacid positions that are conserved in all mammals. As for ERAP2, different computational methods indicated that positive selection has driven the recurrent appearance of protein-destabilizing variants during mammalian evolution. Application of a population-genetics phylogenetics approach showed that purifying selection represented a major force acting on some APP components (e.g. immunoproteasome subunits and chaperones) and allowed identification of positive selection events in the human lineage.We also investigated the evolutionary history of APP genes in human populations by developing a new approach that uses several different tests to identify the selection target, and that integrates low-coverage whole-genome sequencing data with Sanger sequencing. This analysis revealed that 9 APP genes underwent local adaptation in human populations. Most positive selection targets are located within noncoding regions with regulatory function in myeloid cells or act as expression quantitative trait loci. Conversely, balancing selection targeted nonsynonymous variants in TAP1 and CD207 (langerin). Finally, we suggest that selected variants in PSMB10 and CD207 contribute to human phenotypes. Thus, we used evolutionary information to generate experimentally-testable hypotheses and to provide a list of sites to prioritize in follow-up analyses.     

Suppression of the Macrophage Proteasome by Ethanol Impairs MHC Class I Antigen Processing and Presentation

Alcohol binge-drinking (acute ethanol consumption) is immunosuppressive and alters both the innate and adaptive arms of the immune system. Antigen presentation by macrophages (and other antigen presenting cells) represents an important function of the innate immune system that, in part, determines the outcome of the host immune response. Ethanol has been shown to suppress antigen presentation in antigen presenting cells though mechanisms of this impairment are not well understood. The constitutive and immunoproteasomes are important components of the cellular proteolytic machinery responsible for the initial steps critical to the generation of MHC Class I peptides for antigen presentation. In this study, we used an in-vitro cell culture model of acute alcohol exposure to study the effect of ethanol on the proteasome function in RAW 264.7 cells. Additionally, primary murine peritoneal macrophages obtained by peritoneal lavage from C57BL/6 mice were used to confirm our cell culture findings. We demonstrate that ethanol impairs proteasome function in peritoneal macrophages through suppression of chymotrypsin-like (Cht-L) proteasome activity as well as composition of the immunoproteasome subunit LMP7. Using primary murine peritoneal macrophages, we have further demonstrated that, ethanol-induced impairment of the proteasome function suppresses processing of antigenic proteins and peptides by the macrophage and in turn suppresses the presentation of these antigens to cells of adaptive immunity. The results of this study provide an important mechanism to explain the immunosuppressive effects of acute ethanol exposure.     

Rapid immunoassay to detect antibodies against human T-cell lymphotropic virus type 1 (HTLV-1) by the recombinant immunodominant antigens

A rapid immunochromatographic assay, using the recombinant immunodominant antigens of HTLV-1, has been developed to detect circulating antibodies to HTLV-1. The method was compared with an enzyme-linked immunosorbent assay by evaluating 1,631 serum or plasma samples. This HTLV-1 rapid assay was easy to perform and required no special equipment which provided visual result within 5 min with an excellent sensitivity and specificity in detecting HTLV-1 infection.     

Two endogenous protein kinase activities in heterogeneous nuclear ribonucleoprotein particles (hnRNP)

Two protein kinase activities which differ in their catalytic activity towards endogenous and exogenous substrates have been detected and partially purified from heterogeneous nuclear ribonucleoprotein particles (hnRNP).Abbreviations hnRNP heterogeneous nuclear ribonucleoprotein particles - MOPS 3-[N-Morpholino] propanesulphonic acid - MES 2-[N-Morpholino] ethanesulphonic acid - IBMX isobutylmethylxanthine     

Tumor-Associated Antigen Peptides as Anti-Metastatic Vaccines

Summary Cytotoxic T-lymphocytes (CTLs) kill abnormal cells. CTLs recognize major histocompatibility complex class I molecules in complex with peptides derived from relevant antigens. The identification of tumor associated antigen peptides enabled the design of anti-tumor and anti-metastatic vaccines in a murine lung carcinoma.     

Tumor-Associated Antigen Peptides as Anti-Metastatic Vaccines

Cytotoxic T-lymphocytes (CTLs) kill abnormal cells. CTLs recognize major histocompatibility complex class I molecules in complex with peptides derived from relevant antigens. The identification of tumor associated antigen peptides enabled the design of anti-tumor and anti-metastatic vaccines in a murine lung carcinoma.     

A Viral,Transporter Associated with Antigen Processing (TAP)-independent,High Affinity Ligand with Alternative Interactions Endogenously Presented by the Nonclassical Human Leukocyte Antigen E Class I Molecule

The transporter associated with antigen processing (TAP) enables the flow of viral peptides generated in the cytosol by the proteasome and other proteases to the endoplasmic reticulum, where they complex with nascent human leukocyte antigen (HLA) class I. Later, these peptide-HLA class I complexes can be recognized by CD8⁺ lymphocytes. Cancerous cells and infected cells in which TAP is blocked, as well as individuals with unusable TAP complexes, are able to present peptides on HLA class I by generating them through TAP-independent processing pathways. Here, we identify a physiologically processed HLA-E ligand derived from the D8L protein in TAP-deficient vaccinia virus-infected cells. This natural high affinity HLA-E class I ligand uses alternative interactions to the anchor motifs previously described to be presented on nonclassical HLA class I molecules. This octameric peptide was also presented on HLA-Cw1 with similar binding affinity on both classical and nonclassical class I molecules. In addition, this viral peptide inhibits HLA-E-mediated cytolysis by natural killer cells. Comparison between the amino acid sequences of the presenting HLA-E and HLA-Cw1 alleles revealed a shared structural motif in both HLA class molecules, which could be related to their observed similar cross-reactivity affinities. This motif consists of several residues located on the floor of the peptide-binding site. These data expand the role of HLA-E as an antigen-presenting molecule.     

Antigen traffic pathways in dendritic cells

Dendritic cells (DC) are now believed to be the principal initiators of T cell-mediated immune responses. Their location in body tissues, migratory behaviour in response to inflammatory stimuli, endocytic properties, expression of MHC molecules and key T cell stimulatory molecules and many other attributes place these remarkable cells in a unique and influential position in the immune system. Progress in DC culture methods has recently allowed in-depth studies on the cell biological features that enable them to fulfil their crucial role in the immune response.     

The Cellular Redox Environment Alters Antigen Presentation

Cysteine-containing peptides represent an important class of T cell epitopes, yet their prevalence remains underestimated. We have established and interrogated a database of around 70,000 naturally processed MHC-bound peptides and demonstrate that cysteine-containing peptides are presented on the surface of cells in an MHC allomorph-dependent manner and comprise on average 5–10% of the immunopeptidome. A significant proportion of these peptides are oxidatively modified, most commonly through covalent linkage with the antioxidant glutathione. Unlike some of the previously reported cysteine-based modifications, this represents a true physiological alteration of cysteine residues. Furthermore, our results suggest that alterations in the cellular redox state induced by viral infection are communicated to the immune system through the presentation of S-glutathionylated viral peptides, resulting in altered T cell recognition. Our data provide a structural basis for how the glutathione modification alters recognition by virus-specific T cells. Collectively, these results suggest that oxidative stress represents a mechanism for modulating the virus-specific T cell response.     

Methods and protocols for prediction of immunogenic epitopes

T-cell recognition of peptide/major histocompatibility complex (MHC) is a prerequisite for cellular immunity. Recently, there has been an influx of bioinformatics tools to facilitate the identification of T-cell epitopes to specific MHC alleles. This article examines existing computational strategies for the study of peptide/MHC interactions. The most important bioinformatics tools and methods with relevance to the study of peptide/MHC interactions have been reviewed. We have also provided guidelines for predicting antigenic peptides based on the availability of existing experimental data.     

MHC antigen expression by melanomas recovered from mice treated with allogeneic mouse fibroblasts genetically modified for interleukin-2 secretion and the expression of melanoma-associated antigens

Recent approaches toward the immunotherapy of neoplastic disease involve the introduction of expression-competent genes for interleukin-2 (IL-2) into autologous malignant cells. Treatment of tumor-bearing experimental animals with the IL-2-secreting cells successfully induces partial and at times complete remissions. In most instances, however, although delayed, progressive tumor growth continues. Here, certain of the characteristic of B16 melanomas (H-2^b) persisting in C57BL/6 mice (H-2^b) treated with an IL-2-secreting, melanoma-antigen-positive cellular immunogen (RLBA-IL-2 cells) are described. Unlike the melanoma cells first injected, B16 cells recovered from mice treated with RLBA-IL-2 cells were deficient in the experssion of MHC class I, but not class II determinants. Deficient MHC class I expression correlated with the cells' resistance to cytotoxic T lymphocytes (CTL) from the spleens of mice immunized with RLBA-IL-2 cells. Melanomas persisting in mice treated with non-IL-2-secreting, melanoma-antigen-positive cell constructs (RLBA-ZipNeo cells) were also deficient in the expression of MHC class I determinants, and the melanoma cells were resistant to CTL from mice immunized with RLBA-ZipNeo cells. Thus, the expression of melanoma-associated antigens rather than IL-2-secretion correlated with deficient MHC class I expression by the persistent melanomas. This point was substantiated by the expression of MHC class I antigens by melanomas persisting in mice treated with IL-2-secreting, melanoma-antigen-negative LM cells (LM-IL-2); it was equivalent to that of melanomas in untreated mice. The involvement of MHC class I antigens in the immune resistance of persistent melanoma cells from mice treated with the melanoma-autigen-positive immunogens was indicated by the effect of interferon (IFN) orN-methyl-N-nitro-N-nitrosoguanidine (MNNG) on the susceptibility of the cells to anti-melanoma CTL. Treatment of the resistant melanomas with IFN or MNNG stimulated MHC class I antigen expression and restored the cells' sensitivity to CTL from mice immunized with IL-2-secreting or nonsecreting, melanoma-antigen-positive cellular immunogens. Prior treatment of the treated cells with antibodies to MHC class I determinants inhibited the cells' susceptibility to CTL from mice immunized with RLBA-IL-2 cells.     

Shifting patterns: malaria dynamics and rainfall variability in an African highland

The long-term patterns of malaria in the East African highlands typically involve not only a general upward trend in cases but also a dramatic increase in the size of epidemic outbreaks. The role of climate variability in driving epidemic cycles at interannual time scales remains controversial, in part because it has been seen as conflicting with the alternative explanation of purely endogenous cycles exclusively generated by the nonlinear dynamics of the disease. We analyse a long temporal record of monthly cases from 1970 to 2003 in a highland of western Kenya with both a time-series epidemiological model (time-series susceptible-infected-recovered) and a statistical approach specifically developed for non-stationary patterns. Results show that multiyear cycles of malaria outbreaks appear in the 1980s, concomitant with the timing of a regime shift in the dynamics of cases; the cycles become more pronounced in the 1990s, when the coupling between disease and rainfall is also stronger as the variance of rainfall increased at the frequencies of coupling. Disease dynamics and climate forcing play complementary and interacting roles at different temporal scales. Thus, these mechanisms should not be viewed as alternative and their interaction needs to be integrated in the development of future predictive models.