Characterization of the circulating antigen of Toxoplasma gondii.

Circulating antigen of Toxoplasma gondii has been shown to be antigenically distinct from haemagglutinating or peritoneal exudate antigen. It is composed of two components that have molecular weights of approximately 150,000 and 324,000 daltons. Treatment of rats wih cyclophosphamide stopped both the production of circulating antigen and dye test-specific antibody without affecting the parasite yield. Immune lysis appears to be the major pathway for production of circulating antigen, although other possible mechanism of release are discussed.