Mechanisms of resistance to Leishmania aethiopica. I. Interferon-gamma in combination with a cytokine (not tumor necrosis factor-alpha) is required, but cannot act alone in the inhibition of intracellular forms of L. aethiopica in THP1 cells.

Following exposure to promastigotes of various Leishmania species, mononuclear cells from non-exposed as well as potentially exposed individuals produced a cytokine response which inhibited intracellular forms of Leishmania aethiopica in a permissive monocytic cell line (THP1). Interferon-gamma (IFN-gamma), was one of the cytokines responsible for this anti-leishmanial effect. IFN-gamma was necessary for inhibition but could not act on its own inhibiting L. aethiopica. Tumor necrosis factor-alpha seemed not to be involved in the anti-L. aethiopica effect. The observed effects were in the absence of endotoxin. The results suggest that the mechanisms of killing of L. aethiopica in human cells may differ from those responsible for inhibition of other Leishmania parasites (such as Leishmania major) in mouse macrophages. Furthermore, that potentially relevant responses to Leishmania antigens may exist in normal individuals.