T-cell determinants and antibody binding sites on the major mycobacterial secretory protein MPB59 of Mycobacterium bovis.

Among the first proteins encountered by the host immune system upon infection or vaccination with mycobacteria are those secreted by the bacillus during growth. The antigen 85 complex of Mycobacterium bovis bacillus Calmette-Gúerin (BCG) is composed of three closely related members. The mature 85B protein of M. bovis (MPB59) has a high degree of amino acid identity with the M. bovis 85A protein (76%) and the Mycobacterium tuberculosis 85B (99%) and 85A (76%) proteins. We have examined the regions of MPB59 which stimulate human T- and B-cell responses by use of a set of 28 synthetic peptides, 20 amino acids (aa) in length and overlapping by 10 aa. Initial proliferative assays with recombinant MPB59 demonstrated that peripheral blood mononuclear cells from 95% of BCG vaccinees and 52% of tuberculosis patients responded to the whole mature protein. Peripheral blood mononuclear cells from MPB59 responders, but not nonresponders, were stimulated by peptides in a dose-dependent fashion. Five peptides were reactive in more than half of the MPB59 responders. The T-cell-reactive regions were essentially identical in the M. bovis and M. tuberculosis 85B proteins. Subjects with a variety of HLA-DR phenotypes responded to a number of these peptides. The dominant T-cell-reactive regions were distinct from the peptides recognized by sera from tuberculosis patients (aa 71 to 100) and the murine monoclonal antibody HYT27 (aa 61 to 90). The region reactive with antibodies overlapped part of the MPB59 sequence recently shown to participate in the binding of MPB59 to fibronectin.