Analysis of the interaction of peptide hen egg white lysozyme (34-45) with the I-Ak molecule.

We examined the structural characteristics of a peptide Ag that determine its ability to interact with class II-MHC molecules and TCR. The studies reported here focused on recognition of the hen egg white lysozyme (HEL) tryptic fragment HEL(34-45) by two I-Ak-restricted T cell hybridomas. HEL(34-45) bound to I-Ak created more than one antigenic specificity. Experiments with truncated peptides and alanine-substituted peptides indicated that two T cell hybrids either recognized distinct regions of the HEL(34-45) peptide, or different determinants generated by interaction of the peptide with I-Ak. Although we identified residues of HEL(34-45) that were critical to T cell recognition, no positions in the peptide were identified as I-Ak contact sites using single alanine substitutions. This suggests that more than one site or region of the peptide contributes to the binding to I-Ak. Finally, the murine lysozyme equivalent of 34-45 did not bind to I-Ak. Substitution of the corresponding murine lysozyme (self) residue at position 41 of HEL(34-45) abrogated I-Ak binding of the peptide.