H-2-ASSOCIATED EFFECTS OF FLANKING RESIDUES ON THE RECOGNITION OF A PERMISSIVE MYCOBACTERIAL T-CELL EPITOPE

Previously we have identified an immunodominant, eight-residue, epitop e core sequence (TAAGNVNI) from the 19 000 MW protein of Mycobacterium tuberculosis, which is recognized in the context of multiple H-2 I-A molecules. In this study, the role of residues flanking this T-cell ep itope core was examined, using a series of 20 mer analogue peptides in which the native flanking residues were progressively replaced with L -alanine. Analogue peptides were tested for their capacity to stimulat e a CD4(+) 19 000 MW protein-specific T-cell line, revealing that all but one N-terminal flanking residue could be replaced collectively by alanine without significant loss of stimulatory activity. However, cle ar H-2-associated differences in the requirement for flanking residues were demonstrated with peptide-specific T-cell hybridomas. In particu lar, H-2(d)-derived hybridomas were much more stringent in their requi rement for flanking residues than were H-2(b) hybridomas. All polyalan ine-substituted peptides bound I-A(b) molecules, with affinities simil ar to the native unsubstituted peptide. In contrast, significantly red uced binding to I-A(d) was observed with several analogue peptides, al though without a clear relationship to the degree of substitution. Fur thermore, in H-2(b) mice, neither immunogenicity nor cross-reactivity with the native peptide showed a clear inverse relationship with respe ct to the degree of alanine substitution. The results presented in thi s paper indicate that flanking residues can influence T-cell specifici ty and that these effects may be controlled by major histocompatibilit y complex (MHC) haplotype.