Role of T Cell Subsets in the Modulation of Mycobacterium avium Growth within Human Monocytes

Mycobacterium avium frequently causes disseminated disease in patients with advanced AIDS with low CD4 counts. The effects of T lymphocyte on intracellular M. avium replication were examined. Plastic adherent monocytes and nonadherent lymphocytes were separated from peripheral blood mononuclear cells. After infection with M. avium, monocytes were cultured with or without autologous lymphocytes (1–10 cells/monocyte) for up to 7 days. Addition of lymphocytes to M. avium-infected monocytes significantly decreased intracellular M. avium growth after 7 days culture (n = 11, P < 0.01, paired t test) and increased IFN-γ production compared to monocytes alone. Neutralizing IFN-γ partially abrogated lymphocyte activity. CD4 depletion diminished anti-mycobactericidal effects and CD8+ lymphocytes increased intracellular M. avium growth (P < 0.05, n = 5, t test). These data suggest that interactions between monocytes and nonadherent cell fractions such as CD4+ T cells and NK cells are important in intracellular M. avium growth modulation in monocytes from healthy humans.