Interferon-γ Production by Human T Cells and Natural Killer Cells In Vitro in Response to Antigens from the Two Intracellular Pathogens Mycobacterium tuberculosis and Leishmania major

Acquired resistance to both mycobacteria and Leishmania is primarily mediated by interferon-γ (IFN-γ), which triggers mechanisms leading to the death of the microorganism in macrophages. In this study, cell activation and IFN-γ production was investigated in human peripheral blood mononuclear cells (PBMC) from individuals previously sensitized to tuberculin and without known exposure to Leishmania parasites. Immune staining for intracellular IFN-γ and surface markers allowed flow cytometric identification of the cellular sources of IFN-γ in cell cultures incubated with purified protein derivative of tuberculin (PPD) and Leishmania antigens. It was found that IFN-γ was produced in response to both PPD and Leishmania stimulant by T cells in the cultures. Activation of IFN-γ producing natural killer (NK) cells was demonstrated only in some cultures, and only with concomitant T cell activation.