Induction of toxoplasmostasis in a human glioblastoma by interferon gamma

In the course of human toxoplasmosis central nervous system involvement often occurs. As a model for toxoplasma growth within human brain cells the proliferation of Toxoplasma gondii strain BK within the human glioblastoma cell line 86HG39 was analysed. We found that 86HG39 cells support the growth of toxoplasma similar to human monocyte derived macrophages and in contrast to human monocytes. The growth of Toxoplasma gondii within interferon gamma (IFN gamma) treated 86HG39 cells is reduced due to toxoplasmostasis and not due to toxoplasmocide effects. The mechanism of IFN gamma induced toxoplasmostasis was also investigated. It was found that IFN gamma did not induce O2- production and/or nitrite oxide production, and inhibitors of O2- and NO2- did not influence IFN gamma induced toxoplasmostasis. In contrast, the supplementation of L-tryptophan to the culture medium completely abolished the IFN gamma effect. We therefore conclude that the induction of L-tryptophan degradation in 86HG39 cells by IFN gamma, possibly by activation of the indoleamine-2,3-dioxygenase, is responsible for the IFN gamma induced toxoplasmostasis within the glioblastoma cell line.