Gammadelta T cells and Mycobacterium tuberculosis.

Since the first descriptions of mycobacterial reactivity for gammadelta T cells in 1989, studies of gammadelta T-cell responses to M. tuberculosis in humans and animal models have increased our understanding of the complex role(s) of this T-cell subset not only in the immune response to M. tuberculosis, but also to microbial pathogens in general. Although CD4+ T cells remain the dominant and critical T-cell subset in protection against M. tuberculosis, gammadelta T cells appear to have an important complementary role, which may be primarily expressed in and around maturing granulomas. This is a difficult area to study in humans. Gammadelta T cells are potent sources of IFN-gamma and competent cytotoxic effector cells, but differ from CD4+ T cells in the antigens they recognize and the manner in which M. tuberculosis-infected macrophages process and present antigens to these two subsets. One of the most fascinating features of Vgamma9/Vgamma2+ gammadelta T cells is their responsiveness to non-peptidic molecules. Solving the mechanism(s) of antigen recognition and presentation of these molecules to gammadelta T cells should help determine whether gammadelta T cells are responding to universal 'supernatigen'-like motifs expressed by a broad range of microbes or in fact discriminate among a diversity of peptidic and nonpeptidic microbial antigens. Enhanced understanding of the function of and antigen recognition by Vgamma9+/Vgamma2+ T cells is not only important for immunity to M. tuberculosis but also for T-cell responses to microbial pathogens in general.