Mapping of V beta 11+ helper T cell epitopes on mycobacterial antigen in mouse primed with Mycobacterium tuberculosis.

Antigenic epitopes for Mycobacterium tuberculosis-reactive T cell immune responses have been mapped using the purified Mycobacterium protein antigen. Lymph node cells from C57BL/6 mice that had been immunized with heat-killed M. tuberculosis were cultured with various Mycobacterium protein antigens and their reactivity was monitored by proliferative response. Usage of the TCR β chain repertoire was analyzed by flow cytometry. Stimulation of M. tuberculosis-primed lymph node cells with MPT59 (antigen 85B, α antigen) induced proliferative response, production of IL-2 and IFN-γ, and the expansion of Vβ11 CD4F T cells in conjunction with antigen-presenting cells in an I-Ab-restricted manner. Lymph node cells from non-primed mice failed to proliferate in response to MPT59. Using peptides covering the complete mature 285 amino acids long MPT59 protein as 15-mer molecules overlapping by five amino acids, we identified the antigenic epitope for MPT59-specific Vβ11 T cells. The 15-mer peptide, covering amino acid residues 240–254 of MPT59 [peptide-25 (amino acids 240–254)], contains the motif that is conserved for I-Ab and requires processing by antigen-presenting cells to trigger peptide-25specific Vβ11 CD4F T cells. We conclude from these results that MPT59 and peptide-25 (amino acids 240–254) are not superantigens and require antigen processing in order to stimulate Vβ11 Th1 cells. This experimental system will provide us with a useful tool for delineating the regulation of T cell development in a particular subset of M. tuberculosis infection and for developing antigenic peptides for Th1-dominant immune responses.