The enhancing effect of interferon-β and -γ on the killing of Leishmania tropica major in human mononuclear phagocytes in vitro

Both native human IFN-β or -γ added to human monocytes in culture increased their leishmaniacidal effect on intracellular Leishmania tropica major (L. major) amastigotes. This effect was dose-dependent, and was apparent if the IFN was added either before or after infection of the monocyte cultures with the promastigote form of the parasite. Compared on the basis of antiviral activity, IFN-γ was shown to have a leishmaniacidal effect approximately three times greater than IFN-β. Recombinant IFN preparations showed similar effects. In addition, IFN-γ increased H₂O₂ production from human monocytes in culture in a dose-dependent manner. Monoclonal antibody to IFN-γ abrogated both its effect on the leishmaniacidal capacity and on H₂O₂ production by the monocytes. These results suggest that IFN-γ may be of therapeutic value in cutaneous leishmaniasis.