Gamma interferon-induced inhibition of Toxoplasma gondii in astrocytes is mediated by IGTP

Toxoplasma gondii is an important pathogen in the central nervous system, causing a severe and often fatal encephalitis in patients with AIDS. Gamma interferon (IFN-γ) is the main cytokine preventing reactivation of Toxoplasma encephalitis in the brain. Microglia are important IFN-γ-activated effector cells controlling the growth of T. gondii in the brain via a nitric oxide (NO)-mediated mechanism. IFN-γ can also activate astrocytes to inhibit the growth of T. gondii. Previous studies found that the mechanism in murine astrocytes is independent of NO and all other known anti-Toxoplasma mechanisms. In this study we investigated the role of IGTP, a recently identified IFN-γ-regulated gene, in IFN-γ inhibition of T. gondii in murine astrocytes. Primary astrocytes were cultivated from IGTP-deficient mice, treated with IFN-γ, and then tested for anti-Toxoplasma activity. In wild-type astrocytes T. gondii growth was significantly inhibited by IFN-γ, whereas in astrocytes from IGTP-deficient mice IFN-γ did not cause a significant inhibition of growth. Immunoblot analysis confirmed that IFN-γ induced significant levels of IGTP in wild-type murine astrocytes within 24 h. These results indicate that IGTP plays a central role in the IFN-γ-induced inhibition of T. gondii in murine astrocytes.