Circulating antigen of Toxoplasma gondii in patients with AIDS: significance of detection and structural properties.

232 sera and 40 cerebrospinal fluid samples of altogether 125 patients in stages III or IV of a HIV-infection were tested for circulating antigen of Toxoplasma gondii by means of a three-layer enzyme-linked immunosorbent assay. Circulating antigen was detected in 32 sera of 20 patients (= 16% of all persons investigated). These ELISA results were reexamined by an Immunoblot following a SDS-PAGE and confirmed in most cases. In addition, this test system led to a partial characterization of the circulating antigen; it consists of at least two proteins with atomic mass units of 27 and 57 kd respectively. The antigenemia was correlated with IgG- and IgM-antibody titres, with clinical symptoms, and with pathological findings also. Our results indicate that the detection of circulating antigen in sera offers a rapid and efficient method for the diagnosis of an acute toxoplasmosis in AIDS-patients.