Comparative study of three immunoassays for detection of immunoglobulin M antibodies against Toxoplasma gondii.

Immunoglobulin M antibodies against a major serological antigen (Mr 6 kD) were detected in human sera by indirect ELISA, antibody capture ELISA, and immunoblot test. In contrast to indirect ELISA, the immunoblot test gave no false positive reactions, not even with those sera containing a high level of rheumatoid factor. However, the immunoblot test gave false negative results with sera which gave positive results in both ELISA tests. The antibody capture ELISA gave no false negative reactions. All positive sera except one reacted specifically with Toxoplasma gondii antigens.