CONSERVED T-CELL RECEPTOR CLASS-II MAJOR HISTOCOMPATIBILITY COMPLEX CONTACT DETECTED IN A T-LYMPHOCYTE POPULATION

T-cell receptor (TCR) interacts with an antigenic peptide deeply burie d in the major histocompatibility complex (MHC) molecule. How class II MHC is contacted by TCR during antigen recognition remains largely el usive. Here we used a panel of I-E-k mutants to identify two I-E-k res idues that were frequently contacted by TCR among a large pool of T ce lls specific for the same antigen. The restricted TCR interaction with I-E-k was independent of the antigen peptides. We also identified a d ominant heteroclitic residue oil I-E-k, beta 81H, in which mutation le d to increased recognition of antigens in individual T-cell clo:les. M oreover, both the conserved TCR-I-E-k interaction and the heteroclitic TCR-I-E-k recognition were detected in T lymphocytes freshly isolated from mice primed with the specific antigens. The identical TCR-I-E-k interaction in a heterogeneous T-cell population suggested the dominan ce of invariant TCR-class II MHC interaction.