Effects of MHC II conformation and pH on the recognition of peptide by T cells.
In this study we analysed the binding of the peptide HEL46-61 to purified Ak molecules which have been altered by site-directed mutagenesis at polymorphic positions to include amino acids from the Ad alpha-chain. We find that changes in the floor of the peptide binding groove, at positions 11, 14 and 28, abolish T cell recognition without changing peptide binding affinity. We further show that amino acid changes at these positions in the Ad molecule result in a conformationally altered molecule as evidenced by loss of binding of the Ad alpha specific monoclonal antibody K24. Thus the T cell receptor is highly sensitive to subtle changes in MHC II structure induced at sites that are unlikely to be involved in direct T cell contact. This has important implications with respect to allorecognition. The binding studies reported here were performed both at pH 7, to reflect binding of peptides at the cell surface, and at pH 5.5, to mimic binding in an intracellular acidic compartment. Binding to wild-type Ak was increased 2-3-fold at pH 5.5, whereas binding to some MHC II mutants was increased by greater than 20-fold at pH 5.5 relative to pH 7. These results show that the apparent peptide binding specificity for the mutants differs at pH 7 and 5.5, and suggest that caution should be used in defining the MHC-restriction of peptide epitopes at neutral pH.
Bangia
N
N
Department of Immunology, University of Toronto, Ontario, Canada.
Ghumman
B
B
Watts
T H
TH
D000595:Amino Acid Sequence; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D000941:Antigens / Q000276:immunology*; D002460:Cell Line; D002645:Chickens; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000276:immunology*; D006863:Hydrogen-Ion Concentration; D008213:Lymphocyte Activation / Q000276:immunology; D008969:Molecular Sequence Data; D009113:Muramidase / Q000276:immunology; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation; D013601:T-Lymphocytes / Q000276:immunology*
D000941:Antigens; D000949:Histocompatibility Antigens Class II; D009113:Muramidase