UNRESPONSIVENESS TO A SELF-PEPTIDE OF MOUSE LYSOZYME OWING TO HINDRANCE OF T-CELL RECEPTOR-MAJOR HISTOCOMPATIBILITY COMPLEX PEPTIDE INTERACTION CAUSED BY FLANKING EPITOPIC RESIDUES/

A self-peptide containing amino acid residues 46-61 (NRGDQSTDYGIFQINSR ) of mouse lysozyme (ML) (p46-61, which binds strongly to the A(k) mol ecule but does not bind to the E(k) molecule), can induce a strong pro liferative T cell response in CBA/J mice (A(k), E(k)) but no response at all in B10.A(4R) mice (A(k), E(o)). However, two truncated forms of p46-61, p48-61, or p46-59, are immunogenic in both B10.A(4R) and CBA/ J mice. The critical residues within p46-61 reside between amino acid positions 51 and 59. T cells of B10.A(4R) mice primed with the truncat ed peptides in vivo cannot be restimulated by p46-61 in vitro. This su ggests that T cell receptor (TCR) contact (epitopic) residue(sf flanki ng the minimal 51-59 determinant within p46-61 hinder the interaction of the p46-61/A(k) complex with the appropriate TCR(s), thereby causin g a lack of proliferative T cell response in this mouse strain. Unlike B10.A(4R) mice, [B10.A(4R)XCBA/J]F1 mice responded vigorously to p46- 61, suggesting that thymic APC of B10.A(4R) mice do not present a self ligand to T cells resulting in a p46-61-specific hole in the T cell r epertoire in B10.A(4R) or the F1 mice. Moreover, APC h-om B10.A(4R) mi ce are capable of efficiently presenting p46-61 to peptide-specific T cell lines from CBA/J mice. The proliferative unresponsiveness of B10. A(4R) mice to p46-61 is not due to non-major histocompatibility comple x genes because B10.A mice (A(k), E(k)) respond well to p46-61. Intere stingly, B10.A(4R) mice can raise a good proliferative response to p46 -61(R61A) (in which the arginine residue at position 61 (R61) of p46-6 1 had been substituted by an alanine residue) or equally well to p46-6 1 (R61L/F/N/K), indicating that R61 was indeed responsible for hinderi ng the interaction of p46-61 with the appropriate TCR. Finally, chimer ic mice [B10.A(4R)-->B10.A] responded vigorously to p46-61, suggesting that thymic antigen presentation environment of the B10.A mouse was c ritical for development of a p46-61-reactive T cell repertoire. Thus, we provide experimental demonstration of a novel mechanism for unrespo nsiveness to a self peptide, p46-61, in the B10.A(4R) mouse owing to h indrance: in this system it is the interaction between the available T CR and the A(k)/p46-61 complex, which is hindered by epitopic residue( s) within p46-61. We argue that besides possessing T cells that are hi ndered by R61 of p46-61, CBA/J and B10.A mice have developed an additi onal subset of T cells bearing TCRs which are not hinderable by R61, p resumably through positive selection with peptides derived from class II E(k), or class I D-k/D-d molecules. These results have important im plications in self tolerance, shaping of the T cell repertoire, and in defining susceptibility to autoimmunity.