Detection of circulating antigens of Toxoplasma gondii in human infection.

Seventy-nine serum specimens from pregnant women and 29 from immunocompromised patients (12 from graft recipients and 17 from patients with acquired immunodeficiency syndrome) were classified into three groups according to their serologic status to Toxoplasma gondii as determined by immunofluorescence and an enzyme-linked immunosorbent assay (ELISA): no antibodies (group 1), acute acquired infection (group 2), and reactivation (group 3). These samples were tested for the presence of circulating antigens (CAg) of T. gondii by capture ELISA and immunoblotting. The presence of CAg was detected by at least one of the two techniques in six of 31 subjects in group 1, 51 of 68 subjects in group 2, and seven of nine subjects in group 3. Of a total of 108 serum specimens, 28 were found to be T. gondii-positive by capture ELISA, 57 by immunoblotting, and 21 by both techniques. Among the nine polypeptides detected by immunoblotting, 38 recognized p14, 17 recognized p8, and 16 recognized p8, and 16 recognized p30. These results demonstrate that the detection of CAg can aid in the diagnosis of infection by T. gondii in humans, especially in immunocompromised patients whose serologic response can be impaired.