Molecular mechanisms of class I major histocompatibility complex antigen processing and presentation

The presentation of antigenic peptides by class I major histocompatibility complex molecules plays a central role in the cellular immune response, since immune surveillance for detection of viral infections or malignant transformations is achieved by CD8+ T lymphocytes which inspect peptides, derived from intracellular proteins, bind to class I molecules on the surface of most cells. The transporter associated with antigen processing selectively translocates cytoplasmically derived peptides of appropriate sequence and length into the lumen of the endoplasmic reticulum where they associate with newly synthesized class I molecules. The translocated peptides are generated by multicatalytic and multisubunit proteasomes which degrade cytoplasmic proteins in a ATP-ubiquitin-dependent manner. This review discusses our current molecular understanding of class I antigen processing and presentation.     

TAP-dependent major histocompatibility complex class I presentation of soluble proteins using listeriolysin

Immunization of mice with mixtures of listeriolysin, a pore-forming hemolysin secreted by the pathogenic bacterium Listeria monocytogenes, together with soluble ovalbumin, nucleoprotein of influenza virus, or beta-galactosidase of Escherichia coli, resulted in strong cytotoxic CD8 T cell responses to each of the respective passenger proteins in vivo. Also, the concomitant addition of either protein with listeriolysin to target cells elicited efficient sensitization of these cells which could be attributed to the pore-forming activity of listeriolysin. This response was dependent upon a functional TAP transporter and was inhibitable by brefeldin A, indicating the transfer of the soluble proteins into the cytosol and the classical major histocompatibility (MHC) class I presentation pathway. The treatment of target cells with listeriolysin under our experimental conditions did not affect cell viability and the pores generated by listeriolysin treatment were repaired within 60 min. Introduction of soluble proteins into the MHC class I presentation pathway by listeriolysin provides a powerful system to study the cytotoxic response towards intracellular pathogens and would allow for rapid screening of potential antigens in vaccine formulations.     

Helicobacter pylori infection in immunized mice lacking major histocompatibility complex class I and class II functions

The role of major histocompatibility complex (MHC) class I- and class II-restricted functions in Helicobacter pylori infection and immunity upon oral immunization was examined in vivo. Experimental challenge with H. pylori SS1 resulted in significantly greater (P 相似文献   

Cell stress-regulated human major histocompatibility complex class I gene expressed in gastrointestinal epithelium

Conventional major histocompatibility complex (MHC) class I genes encode molecules that present intracellular peptide antigens to T cells. They are ubiquitously expressed and regulated by interferon gamma. Two highly divergent human MHC class I genes, MICA and MICB, are regulated by promoter heat shock elements similar to those of HSP70 genes. MICA encodes a cell surface glycoprotein, which is not associated with beta 2-microglobulin, is conformationally stable independent of conventional class I peptide ligands, and almost exclusively expressed in gastrointestinal epithelium. Thus, this MHC class I molecule may function as an indicator of cell stress and may be recognized by a subset of gut mucosal T cells in an unusual interaction.     

Excessive degradation of intracellular protein in macrophages prevents presentation in the context of major histocompatibility complex class II molecules

The endogenous major histocompatibility complex (MHC) class II presentation pathway allows biosynthesized, intracellular antigens access for presentation to MHC class II-restricted T cells. This pathway has been well documented in B cells and fibroblasts, but may not be universally available in all antigen-presenting cell types. This study compares the ability of different antigen-presenting cells, expressing endogenous C5 protein (fifth component of mouse complement) as a result of transfection, to present their biosynthesized C5 to MHC class II-restricted T cells. B cells and fibroblasts expressing C5 were able to present several epitopes of this protein with MHC class II molecules, whereas macrophages were unable to do so, but readily presented C5 from an extracellular source. However, macrophage presentation of endogenous C5 could be achieved when they were treated with low doses of the lysosomotropic agent ammonium chloride. In the presence of an inhibitor of autophagy, presentation of endogenous C5 was abrogated, indicating that biosynthesized C5 is shuttled into lysosomal compartments for degradation before making contact with MHC class II molecules. Taken together, this suggests that proteolytic activity in lysosomes of macrophages may be excessive, compared with fibroblasts and B cells, and destroys epitopes of the C5 protein before they can gain access to MHC class II molecules. Thus, there are inherent differences in presentation pathways between antigen-presenting cell types; this could reflect their specialized functions within the immune system with macrophages focussing preferentially on internalization, degradation, and presentation of extracellular material.     

Differentiation-stage specific self-peptides bound by major histocompatibility complex class I molecules

We have tested the hypothesis that phenotypic changes of development are accompanied by expression of differentiation-stage specific peptides bound to major histocompatibility complex (MHC) class I molecules. The U937 cell line, when cultured in the presence of phorbol myristate acetate (PMA), undergoes differentiation from monoblasts to macrophage-like cells. The high-performance liquid chromatography profile of peptides eluted from purified human histocompatibility leukocyte antigen class I molecules expressed by U937 treated with PMA differs from that obtained from control, untreated U937 cells. Chemical sequencing of eluted peptides identified a peptide derived from cytomegalovirus in both treated and untreated cells. PMA-treated, but not untreated cells, displayed an additional peptide derived from interleukin 1 beta. Hence, differentiation-induction of U937 is accompanied by the presentation of at least one differentiation-stage specific peptide. Our results indicate that, similar to viral infection, cellular development and transformation is accompanied by the de novo synthesis of proteins which are processed and presented on MHC class I molecules.     

Presentation of exogenous protein antigens on major histocompatibility complex class I molecules by dendritic cells: pathway of presentation and regulation by cytokines

Several recent studies have shown that dendritic cells (DC) pulsed with soluble proteins can present peptide epitopes derived from these exogenous antigens on major histocompatability complex (MHC) class I molecules and induce an antigen-specific cytotoxic T lymphocyte (CTL) response. We provide evidence here that DC use macropinocytosis to capture soluble antigens that are then presented on MHC class I molecules. The presentation of an epitope derived from soluble ovalbumin was transporter associated with antigen presentation (TAP)-dependent, brefeldin A-sensitive, blocked by inhibitors of proteasomes, and resistant to chloroquine. These data suggest that exogenous antigens access the cytosol of DC and are proccessed for presentation via the same pathway described for conventional MHC class I-restricted cytosolic antigens. Proinflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS) reduced the efficiency of ovalbumin presentation via this pathway. This reduced presentation was not due to impaired expression of class I molecules because these substances upregulated the cell surface expression of Kb-molecules comparable to levels induced by interferon-gamma (IFN-gamma) treatment. The addition of IFN-gamma increased ovalbumin presentation even in the presence of TNF-alpha or LPS. These results show that DC might be involved in the cross-priming phenomenon. This could offer the immune system an additional pathway for effective priming of cytotoxic T cells and provide the possibility to activate both CD4 and CD8 T-cell responses.     

Alloantibodies can discriminate class I major histocompatibility complex molecules associated with various endogenous peptides

Molecules encoded by a single major histocompatibility complex class I gene can associate with any one of a large number of peptide ligands. T-cell receptors have the capacity to discriminate among these peptide-class I complexes and in many cases bind only a single peptide-class I complex with sufficient affinity to trigger effector function. In contrast, it is generally assumed that class I-specific alloantibodies are indifferent to peptide heterogeneity, being directed toward allele-specific determinants on the molecule. In this report, three monoclonal antibodies were used to precipitate Kb molecules from cell lysates. Surprisingly, in each case a different set of peptides was found to be associated with Kb as detected by peptide-dependent Kb-specific alloreactive cytolytic T lymphocytes or by biochemical resolution. These results demonstrate that the affinity of binding by alloantibodies can be affected by the endogenous peptide ligand.     

Cathepsins B and D are dispensable for major histocompatibility complex class II-mediated antigen presentation

Antigen presentation by major histocompatibility complex (MHC) class II molecules requires the participation of different proteases in the endocytic route to degrade endocytosed antigens as well as the MHC class II-associated invariant chain (Ii). Thus far, only the cysteine protease cathepsin (Cat) S appears essential for complete destruction of Ii. The enzymes involved in degradation of the antigens themselves remain to be identified. Degradation of antigens in vitro and experiments using protease inhibitors have suggested that Cat B and Cat D, two major aspartyl and cysteine proteases, respectively, are involved in antigen degradation. We have analyzed the antigen-presenting properties of cells derived from mice deficient in either Cat B or Cat D. Although the absence of these proteases provoked a modest shift in the efficiency of presentation of some antigenic determinants, the overall capacity of Cat B-/- or Cat D-/- antigen-presenting cells was unaffected. Degradation of Ii proceeded normally in Cat B-/- splenocytes, as it did in Cat D-/- cells. We conclude that neither Cat B nor Cat D are essential for MHC class II-mediated antigen presentation.     

Major histocompatibility complex class II-dependent antigen presentation by human intestinal endothelial cells

BACKGROUND & AIMS: In the normal gut, human intestinal microvascular endothelial cells (HIMECs) express major histocompatibility complex (MHC) class II molecules. Enhanced expression is found in chronic inflammation. We examined the cytokine regulation of MHC class II molecules and the associated invariant chain (Ii) in HIMECs and investigated whether such cells can process and present a complex protein antigen to T cells. METHODS: Enzyme-linked immunosorbent assay, flow cytometry, immunoelectron microscopy, as well as T-cell activation assay with HIMECs and HLA-DR-restricted T-cell clones were employed. RESULTS: In unstimulated HIMEC monolayers, HLA-DR, -DP, and -DQ and Ii were undetectable at the protein level, but interferon gamma (IFN-gamma) (100 U/mL) induced expression that peaked for DR after 2-3 days, for DP after 4-6 days, for DQ after 10-12 days, and for Ii after 2-3 days. Tumor necrosis factor alpha had no effect alone but enhanced class II expression in combination with IFN-gamma, most notably for DQ and DP. HLA-DR3-restricted and Mycobacterium tuberculosis heat shock 65-kilodalton-specific T-cell clones were activated to produce IFN-gamma in response to relevant antigen presented by IFN-gamma-treated HIMECs. This response was inhibited by blocking monoclonal antibody to HLA-DR and by chloroquine when compared to professional antigen-presenting cells, HIMECs activated T-cell clones quite efficiently. CONCLUSIONS: These data suggest that microvascular endothelial cells can present complex protein antigens in the human gut.     

The presentation of a hepatitis C viral peptide by distinct major histocompatibility complex class I allotypes from two chimpanzee species

A cytotoxic T lymphocyte (CTL) line, derived from the liver of a common chimpanzee (Pan troglodytes) with hepatitis C, specifically recognized a hepatitis C viral 9-mer peptide (KHP-DATYSR in single-letter amino acid code) bound by the major histocompatibility complex (MHC) class I molecule, Patr-A04. This same CTL line also recognized the identical peptide bound by a structurally different class I molecule, Papa-A06, derived from the separate chimpanzee species, Pan paniscus or pygmy chimpanzee. These class I allotypes differ by six amino acids but, in spite of the structural differences, share the same antigen-presenting function. This is the first observation of antigen presentation to a given T cell receptor by different MHC class I allotypes from separate species.     

Efficient presentation of phagocytosed cellular fragments on the major histocompatibility complex class II products of dendritic cells

Cells from the bone marrow can present peptides that are derived from tumors, transplants, and self-tissues. Here we describe how dendritic cells (DCs) process phagocytosed cell fragments onto major histocompatibility complex (MHC) class II products with unusual efficacy. This was monitored with the Y-Ae monoclonal antibody that is specific for complexes of I-Ab MHC class II presenting a peptide derived from I-Ealpha. When immature DCs from I-Ab mice were cultured for 5-20 h with activated I-E+ B blasts, either necrotic or apoptotic, the DCs produced the epitope recognized by the Y-Ae monoclonal antibody and stimulated T cells reactive with the same MHC-peptide complex. Antigen transfer was also observed with human cells, where human histocompatibility leukocyte antigen (HLA)-DRalpha includes the same peptide sequence as mouse I-Ealpha. Antigen transfer was preceded by uptake of B cell fragments into MHC class II-rich compartments. Quantitation of the amount of I-E protein in the B cell fragments revealed that phagocytosed I-E was 1-10 thousand times more efficient in generating MHC-peptide complexes than preprocessed I-E peptide. When we injected different I-E- bearing cells into C57BL/6 mice to look for a similar phenomenon in vivo, we found that short-lived migrating DCs could be processed by most of the recipient DCs in the lymph node. The consequence of antigen transfer from migratory DCs to lymph node DCs is not yet known, but we suggest that in the steady state, i.e., in the absence of stimuli for DC maturation, this transfer leads to peripheral tolerance of the T cell repertoire to self.     

Expression of class II, but not class I, major histocompatibility complex molecules is required for granuloma formation in infection with Schistosoma mansoni

Previous studies have suggested that granulomatous inflammation in schistosomiasis is mediated by CD4+ T helper lymphocytes sensitized to parasite egg antigens. However, CD8+ T cells have also frequently been associated with the immune response to schistosome eggs. To examine more precisely the role of CD4+ and CD8+ T cells in the pathology of the schistosomal infection, we used mice with targeted mutations in major histocompatibility complex (MHC) class II or class I molecules. These mutations lead, respectively, to the virtual absence of CD4+ and CD8+ T cells. The results clearly show that schistosome-infected MHC class II mutant mice failed to form granulomas around parasite eggs. In contrast, infected MHC class I mutant mice displayed characteristic granulomatous lesions that were comparable to those in wild-type control mice. Moreover, lymphoid cells from MHC class II mutant mice were unable to react to egg antigens with either proliferative or cytokine [interferon-gamma, interleukin (IL)-4, IL-10] responses; nor were they able to present egg antigens to specifically sensitized CD4+ T helper cells from infected syngeneic control mice. By comparison, cells from MHC class I mutant mice exercised all these functions in a manner comparable with those from wild-type controls. These observations clearly demonstrate that schistosomal egg granulomas are mediated by MHC class II-restricted CD4+ T helper cells. They also suggest that CD8+ T cells do not become sensitized to egg antigens and play little role, if any, in the pathogenesis of schistosomiasis.     

Cytomegalovirus infection enhances the neointima formation in rat aortic allografts: effect of major histocompatibility complex class I and class II antigen differences

BACKGROUND: The development of chronic rejection has emerged as a major cause of long-term graft failure. Previous studies have demonstrated that cytomegalovirus (CMV) infection is associated with an increased incidence of chronic allograft rejection in renal, cardiac, and aortic allografts. This study was designed to investigate the effects of the major histocompatibility complex (MHC) class I or class II mismatches on CMV-enhanced chronic rejection. METHODS: Aortic transplantation was performed between different inbred rat strain combinations; the Lewis to RP combination was class I-mismatched and Wag/Rij to RP class II-mismatched. At 7, 28, and 90 days after transplantation, the intensity of chronic rejection in mismatched grafts with or without CMV infection was evaluated using histological and immunohistological analysis. RESULTS: The results of this study demonstrated that CMV infection led to an increased influx of monocytes/ macrophages in class I-mismatched grafts at 1 week after transplantation and enhanced infiltration of T lymphocytes in class II-mismatched grafts at 4 weeks. Although more vascular lesions were observed in the class II-mismatched combinations, an intensified neointima formation by CMV infection was observed only in the MHC class I-mismatched allografts. CONCLUSIONS: CMV infection may increase neointima formation of allografts when an MHC class I disparity between donor and recipient is present. This may be associated with the increased perivascular influx of monocytes/macrophages observed in CMV-infected animals early after transplantation.     

Infection of cells with varicella-zoster virus down-regulates surface expression of class I major histocompatibility complex antigens

In vitro assays indicate that both major histocompatibility complex (MHC) class I and II-restricted cytotoxic T lymphocytes are important for recognition of varicella-zoster virus (VZV)-infected cells. This study demonstrates that infection of human fibroblasts with wild-type or recombinant-derived strain Oka VZV results in down-regulation of surface expression of class I MHC heavy chains. Radioactive labeling of infected cells indicated that the amount of newly synthesized class I antigen was similar in uninfected and VZV-infected cells. In addition, immunoblotting showed that the amount of total cellular class I MHC heavy chains was unaffected by VZV infection. These results suggest that the reduction of class I heavy chains on the surface of VZV-infected cells is due to a defect in posttranslational processing. The down-regulation of class I MHC antigens in VZV-infected cells may provide a mechanism for the virus to escape the host immune response.     

Deficient major histocompatibility complex class II antigen presentation in a subset of Hodgkin's disease tumor cells

Hodgkin's disease is a common malignancy of the lymphoid system. Although the scarce Hodgkin and Reed-Sternberg (HRS) tumor cells in involved tissue synthesize major histocompatibility complex (MHC) class II and costimulatory molecules such as CD40 or CD86, it is unclear whether these tumor cells are operational antigen-presenting cells (APC). We developed an immunofluorescence-based assay to determine the number of MHC class II molecules present on the surface of single living HRS cells. We found that in fresh Hodgkin's disease lymph node biopsies, a subset of HRS cells express a substantial number of surface MHC class II molecules that are occupied by MHC class II-associated invariant chain peptides (CLIP), indicating deficient loading of MHC class II molecules with antigenic peptides. Cultured Hodgkin's disease-derived (HD) cell lines, however, were found to express few MHC class II molecules carrying CLIP peptides on the cell surface and were shown to generate sodium dodecyl sulphate (SDS)-stable MHC class II alphabeta dimers. In addition to showing deficient MHC class II antigen presentation in a subset of HRS cells, our results show that the widely used HD-cell lines are not ideal in vitro models for the disease. The disruption of MHC class II-restricted antigen presentation in HRS cells could represent a key mechanism by which these tumor cells escape immune surveillance.