Distinct recognition phenotypes exist for T cell clones specific for small peptide regions of proteins. Implications for the mechanisms underlying major histocompatibility complex-restricted antigen recognition and clonal deletion models of immune response gene defects.

Using synthetic peptides as antigens, it was found that T cell clones of a given haplotype specific for 13-16 amino acid peptides could be clearly distinguished by the varied influence of amino acid substitutions on recognition. This was true for different antigenic determinants within peptides 81-96 and 74-86 of hen egg-white lysozyme, recognized in the context of the I-Ab and I-Ak molecules, respectively. Considerable complexity was demonstrated in the induced T cell repertoire specific for apparently single determinants, which implies that diversity of T cell recognition approaches that for B cells. The implications of the degeneracy of T cell recognition are discussed in the context of mechanisms through which Ia molecules restrict recognition and theories of Ir gene defects.