Lymphocytes expressing Fc gamma receptors suppress antigen-induced proliferation in cells from guinea pigs infected with virulent Mycobacterium tuberculosis.

The immunomodulatory role of T lymphocytes expressing receptors for the Fc portion of IgG (T gamma cells) in BCG-vaccinated guinea pigs following pulmonary infection with a low dose of virulent Mycobacterium tuberculosis H37Rv was studied. Compared to uninfected animals, guinea pigs infected 2 or 4 weeks previously harbored significantly increased percentages of T gamma cells in the peripheral blood (twofold increase) and the spleen (50% increase), and at 4 weeks had nearly fourfold increases in T gamma cells in bronchotracheal lymph nodes draining the infected lungs. Removal of T gamma cells by panning on plastic dishes coated with a monoclonal antibody specific for guinea pig Fc gamma R resulted in significant increases in proliferative responses of splenocytes to Con A and PPD in vitro. Removal of T gamma cells from peripheral blood lymphocytes resulted in significantly increased responses to PPD and to recombinant mycobacterial hsp 65 and hsp 70 antigens. The isolated T gamma cells themselves did not proliferate when stimulated with Con A, PPD, or either of the specific mycobacterial antigens, even in the presence of syngeneic accessory cells. These results suggest that FcR gamma-bearing T cells may play an important immunomodulatory role in pulmonary tuberculosis, principally by suppressing antigen-induced proliferation in the rest of the lymphocyte population.