Cerebral toxoplasmosis. Pathogenesis and host resistance

IFN-γ-mediated immune responses play a central role in resistance against T. gondii in the brain. IFN-γ production by multiple types of cells, including T cells, is required for the resistance. Microglia is one type of the IFN-γ-producing cells that probably play an important role in controlling the parasite. Following the acute stage, the parasite forms cysts (latent stage) in various organs, especially the brain, heart, and skeletal muscle, establishing chronic infection. Infection in immunocompetent individuals is usually unnoticed or a benign, self-limiting illness, and results in a latent chronic infection. Immunosuppression in chronically infected individuals may result in reactivation of a latent infection, which is initiated by disruption of cysts, followed by proliferation of tachyzoites. Such reactivation of T. gondii infection usually presents as toxoplasmic encephalitis (TE). TE has emerged as a major opportunistic infectious disease in the central nervous system in AIDS patients. © 2007