Differential pattern of T cell recognition of the 65-kDa mycobacterial antigen following immunization with the whole protein or peptides.

The 65-kDa stress protein from Mycobacterium bovis (Bacillus Calmette Guérin) elicited T cell proliferation and antibody responses in seven B10 congenic mouse strains with different H-2 haplotypes. To analyze T cell determinants on this antigen, seven peptides corresponding to six predicted T cell epitopes, and one defined B cell epitope were synthesized. Mice were either immunized with the whole antigen and the specificity of the response was ascertained in respect of the six peptides, or mice were immunized with seven of the peptides and tested for proliferative responses to the whole molecule. The results showed that three peptides carried epitopes to which mice responded following injection of the whole molecule and that immunization with two additional peptides could prime for in vitro stimulation with the native antigen. The latter result indicates the feasibility of generating T cell responses to "cryptic" epitopes on proteins by immunizing with peptides. The peptide-specific T cell responses were distinctly influenced by the H-2 haplotype of mouse strains. However, two peptides were recognized by several H-2-disparate mouse strains, and one peptide could be presented by both I-A and I-E molecules. Immunization with several peptides induced a cross-reactive T cell proliferative response to the homologous GroEL protein isolated from E. coli. The amount of cross-reactivity was influenced by the extent of sequence homology between mycobacterial and E. coli proteins and the major histocompatibility complex class II molecule used to present the peptide.