Effector mechanisms of gamma interferon against Toxoplasma gondii

Abstract

Toxoplasma gondii is an intracellular obligate protozoan parasite, Human infection is generally subclinical, but hosts with deffective cellular immunity are at risk of severe disease. In many countries, congenital toxoplasmosis and toxoplasmic encephalitis in HIV-infected individuals are significant causes of morbidity and mortality. We review here the effector mechanisms of gamma interferon, the major cytokine involved in the protection against T gondii The addition of IFN y to cultured infected THPl cells protected against Tgondii infection by an early mechanism involving a reduction in the number of parasitized cells.The reduction in the percentage of parasitized cells obtained by treatment with IFN y is linked to a decrease in parasite and cellular PLA, activity.This is a new effector mechanism of IFN y against T gondii infection. A second effect is by inducing indoleamine-oxigenase (IDO), an enzyme that reduces tryptophan stores.Tryptophan is essential for intracellular growth of T gondii. lnduction of IDO leads to a parasitostatic effect. In human monocytes induction of nitric oxide is not a part of the antitoxoplasmicidal effect induced by IFN y.