Major histocompatibility class II molecules prevent destructive processing of exogenous peptides at the cell surface of macrophages for presentation to CD4 T cells

Abstract

Summary We studied factors affecting major histocompatibility complex class II (MHC‐II)‐restricted presentation of exogenous peptides at the surface of macrophages. We have previously shown that peptide presentation is modulated by surface‐associated proteolytic enzymes, and in this report the role of the binding of MHC‐II molecules in preventing proteolysis of exogenous synthetic peptides was addressed. Two peptides containing CD4 T‐cell epitopes were incubated with fixed macrophages expressing binding and non‐binding MHC‐II, and supernatants were analysed by high‐performance liquid chromatography and mass spectrometry to monitor peptide degradation. The proportion of full‐length peptides that were degraded and the number of peptide fragments increased when non‐binding macrophages were used, leading to reduction in peptide presentation. When MHC‐II molecules expressed on the surface of fixed macrophages were blocked with monoclonal antibody and incubated with peptides and the supernatants were transferred to fixed macrophages, a significant reduction in peptide presentation was observed. Peptide presentation was up‐regulated at pH 5·5 compared to neutral pH, and the latter was found to be the pH optimum of the proteolytic activity of the surface enzymes involved in the degradation of exogenous peptides and proteins. The data suggest that MHC‐II alleles that bind peptides protect them from degradation at the antigen‐presenting cell surface for presentation to CD4 T cells and we argue that this mechanism could be particularly pronounced at sites of inflammation.

Hyperglycaemia is inversely correlated with live M. bovis BCG‐specific CD4+ T cell responses in Tanzanian adults with latent or active tuberculosis

“…Antigen processing of whole mycobacteria‐derived antigens for MHC class II presentation on the surface of antigen presenting cells requires phagocytosis, processing, and intracellular vesicular trafficking to allow the formation of peptide‐MHC‐II complexes . Soluble, exogenous synthetic peptides can be directly loaded onto MHC class II molecules present on the surface of antigen‐presenting cells and presented to CD4 + T cells . Head to head comparison of synthetic peptides versus whole‐mycobacteria to recall immune memory in vitro distinguishes between ex vivo assessment of CD4 + T cell frequencies directed against a specific antigen from the capacity of antigen‐presenting cells to uptake bacteria, process and present bacteria‐derived antigens to CD4 + T cells.…”

Comprehensive Analysis of Contributions from Protein Conformational Stability and Major Histocompatibility Complex Class II-Peptide Binding Affinity to CD4+Epitope Immunogenicity in HIV-1 Envelope Glycoprotein

“…Alternatively, the protease activities could be similar in the different mouse strains, but the MHC-II of the BALB/c strain (I-A d ) could have lower average peptide-binding affinity than the MHC-II of the other mouse strains; and therefore, I-A d protects a smaller fraction of epitope molecules from destruction. MHC-II proteins have been shown to protect epitopes from proteolytic destruction (61)(62)(63). Further studies in the genetically defined MHC backgrounds of mice will be necessary to generalize mechanisms of antigen processing and then extend them to heterogeneous systems such as in humans.…”

Generation of T cell hybridoma as a technique for study the immune response against bacterial infections

“…The results of such studies [5-8, 11,12] have demonstrated an effective processing of bacterial antigens and binding of antigenic fragments to MHC class II molecule for presentation to CD4 T cells. Two epitopes from streptococcal M5 protein (M5 17-31 and M5 308-319) have been studied to investigate the mechanism of Ag processing and presentation using mouse macrophages and T cell hybridomas specific for each epitopes [23][24][25][26][27][28][29]. This approach is the basis for bacterial vaccines development.…”