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, epitope 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 epitope 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 stimulate 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, clear H-2-associated differences in the requirement for flanking residues were demonstrated with peptide-specific T-cell hybridomas. In particular, H-2d-derived hybridomas were much more stringent in their requirement for flanking residues than were H-2b hybridomas. All polyalanine-substituted peptides bound I-Ab molecules, with affinities similar to the native unsubstituted peptide. In contrast, significantly reduced binding to I-Ad was observed with several analogue peptides, although without a clear relationship to the degree of substitution. Furthermore, in H-2b mice, neither immunogenicity nor cross-reactivity with the native peptide showed a clear inverse relationship with respect to the degree of alanine substitution. The results presented in this paper indicate that flanking residues can influence T-cell specificity and that these effects may be controlled by major histocompatibility complex (MHC) haplotype.
D000409:Alanine / Q000276:immunology; D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D000939:Epitopes / Q000276:immunology*; D006183:H-2 Antigens / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D000942:Antigens, Bacterial; D000939:Epitopes; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments; D000409:Alanine