[Investigation of agretopic motifs in T cell responses specific for pigeon cytochrome c related peptides and restricted to I-E molecules]

Abstract

In our previous study, epitopic and agretopic residues of a peptide fragment deduced from pigeon cytochrome c43-58 (p43-58, AEGFSYTDANKNKGIT) and it's analogues in the T cell responses restricted to I-A molecules were determined. It has been shown that amino acid residue position 50 of the p43-58 works as an epitopic which contacts with T cell antigen receptor (TCR) and residues at positions 46 and 54 function as agretopes which contact with I-A molecules. In the present study, epitopic and agbretopic sites were analyzed in T cell proliferative responses that were restricted to the other class II, I-E, molecules. A peptide antigen, 46D50V54R, which had been prepared by substitution of amino acids at positions 46, 50 and 54 of p43-58 with aspartic acid (D), valine (V) and arginine (R), respectively was shown to induce class II restricted T cell responses in B10. A (3R) (I-Ab, I-Eb/k) but not in B10 (I-Ab, I-E-) mice. Similarly, 50V50R which had been prepared by substitution of amino acids at positions 50 and 54 with V and R, respectively induced T cell proliferation in B10. BR mice (I-Ak, I-Ek) but not in B10. A (4R) (I-Ak, I-E-) mice. These findings indicate that the 46D50V54R and 50V54R generate I-E restricted proliferative responses of T lymphocytes in I-Eb/k and I-Ek-carrying mice, respectively. Furthermore, it was shown that residue 50 functions an an epitope and residues 46 and 54 as agretopes in the I-E restricted responses. Almost identical results were obtained when I-E restricted responses of T lymphocytes were analyzed in B10. PL (H-2u) and B10. SM (H-2v) mice. However, sine no I-E negative counterpart strain for these two latter strains is available, complete analysis concerning the epitopic and agretopic functions has not been performed with B10. PL and B10. SM mice. The present findings demonstrate that the functional sites of the p43-58 analogues are preserved is the T cell responses restricted to each I-E haplotype studied. However, when most potent agretopic motif was determined in various mouse strains, the specific amino acid motifs on the agretopic positions were different among various I-E haplotypes. Furthermore, substitution of the epitopic residue showed no influence on the binding affinity between agretopic residues and class II molecules. Thus, these epitope and agretopes appear to function independently.(ABSTRACT TRUNCATED AT 400 WORDS)