Lymphocytes Expressing Fcγ Receptors Suppress Antigen-Induced Proliferation in Cells from Guinea Pigs Infected with VirulentMycobacterium tuberculosis

The immunomodulatory role of T lymphocytes expressing receptors for the Fc portion of IgG (Tγ cells) in BCG-vaccinated guinea pigs following pulmonary infection with a low dose of virulentMycobacterium tuberculosisH37Rv was studied. Compared to uninfected animals, guinea pigs infected 2 or 4 weeks previously harbored significantly increased percentages of Tγ cells in the peripheral blood (twofold increase) and the spleen (50% increase), and at 4 weeks had nearly fourfold increases in Tγ cells in bronchotracheal lymph nodes draining the infected lungs. Removal of Tγ cells by panning on plastic dishes coated with a monoclonal antibody specific for guinea pig FcγR resulted in significant increases in proliferative responses of splenocytes to Con A and PPDin vitro.Removal of Tγ cells from peripheral blood lymphocytes resulted in significantly increased responses to PPD and to recombinant mycobacterial hsp 65 and hsp 70 antigens. The isolated Tγ 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 FcRγ-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.