Abstract
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.

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