ANALYSIS OF FUNCTIONAL SITES ON A PEPTIDE ANTIGEN, P43-58, IN I-A OR I-E-RESTRICTED T-CELL RESPONSES

It has been shown that two different sites (an agretope and an epitope) on a peptide antigen function independently in T cell responses to the antigen. By virtue of these sites, antigens, MHC molecules, and TCRs constitute trimolecule complexes which eventually result in T cell activation. In our previous reports, we have defined that residues 46 and 54 on a synthetic peptide composed of residues 43 - 58 of pigeon cytochrome c (p43 - 58, AEGFSYTDANKNKGIT) and its analogs function as an agretope and residue 50 as an epitope in both I-A(b) and I-A(k)-carrying mice. In the present study, to extend our method to the other MHC class II molecules (I-E), we used two peptide antigens, 46D5OV54R and 5OV54R, which had been prepared by substitution of amino acids at positions, 46, 50 and 54 or 50 and 54 of p43 - 58 with D, V, R or V, R, respectively, and compared the immunogenicity with those of other peptide analogs. The 46D5OV54R was shown to be non-immunogenic in I-A(b)-carrying mice and the 5OV54R was non-immunogenic in I-A(k)-carrying mice. In contrast, the 46D5OV54R or 5OV54R could induce I-E-restricted proliferative responses of T lymphocytes in I-E(b/k)- or I-E(k/k)-carrying mice, respectively. Furthermore, residues 46 and 54 were shown to function as agretopes and residue 50 as an epitope in the I-E-restricted responses as they did in the I-A-restricted responses, even though some differences were seen between peptide - I-E interaction and peptide - I-A interaction. These agretopes and epitope functioned independently.