Identification of mycobacterial peptide epitopes recognized by CD4+ T cells in association with multiple major histocompatibility complex class II molecules.

The mycobacterial 18-, 28-, and 65-kDa proteins are recognized by T cells in association with multiple class II HLA-DR molecules of the major histocompatibility complex (MHC). To identify the epitopes recognized by T cells in association with multiple HLA-DR molecules, we established CD4+ T cell lines and clones and tested them with overlapping synthetic peptides corresponding to the entire amino acid sequence of the 18- and 65-kDa antigens and to the carboxy terminus of the 28-kDa antigen. The T cell lines established against the 18-kDa antigen recognized three different epitopes, one of which was recognized in the presence of antigen-presenting cells from several allogeneic donors. The 65-kDa antigen-reactive T cell lines responded to nine different peptides, two of which were promiscuous with respect to MHC restriction. The T cell clones responding to the 28-kDa antigen proliferated in response to a single peptide from the carboxy terminus. This peptide was recognized by T cell clones in association with HLA-DRw53, which is coexpressed in individuals expressing HLA-DR4, HLA-DR7, and HLA-DR9. The T cells activated in response to the mycobacterial antigen from vaccinated donors belonged to the protective Th1 subset; hence, the peptides recognized in association with multiple HLA-DR molecules should be useful in subunit vaccines against mycobacterial diseases.