Mycobacterial proliferation in macrophages is prevented by incubation with lymphocytes activated in vitro with a...

Antigen A60 from Mycobacterium bovis bacillus Calmette Guérin was shown to trigger both humoral and cellular immune reactions. We explored the ability of A60 to block intracellular proliferation of phagocytosed mycobacteria with a model system involving peritoneal murine macrophages infected with Mycobacterium avium. Mixed lymphocytes from lymph nodes of mice inoculated with A60 hindered intracellular proliferation of this mycobacterium, owing to A60-specific cells, proliferation of which was induced in vitro in an antigen concentration-dependent manner. The lymphokines released by A60-stimulated T lymphocytes in vitro were identified as interleukin 2 (IL2) and interferon-gamma (IFN-gamma): their production showed a clear A60 dose dependence. When supernatants of such induced lymphocyte cultures were incubated with anti-IFN-gamma antibodies, macrophage activation was prevented, whereas anti-IL 2 immunoglobulin had little effect. Treatment of infected macrophages with recombinant IFN-gamma reduced intracellular proliferation of mycobacteria, while exogenous IL 2 and tumor necrosis factor were ineffective. Therefore, A60 elicits in vitro proliferation of T lymphocytes responding specifically to this antigen with production of IFN-gamma, which in turn activates macrophages and prevents multiplication of phagocytosed mycobacteria.