Enzyme-linked immunosorbent assay for detection of soluble Toxoplasma gondii antigen in acute-phase toxoplasmosis.

Sixty-two sera from 51 patients with lymphadenopathy presumed to be due to acute-phase toxoplasmosis were tested for specific IgM class antibodies by both the immunofluorescence antibody to Toxoplasma gondii in sera were first dissociated in 3 M NaSCN. Antigen attached to the solid phase was detected with enzyme-coupled IgG antibody to Toxoplasma antibody to Toxoplasma gondii in sera were first dissociated in 3 M NaSCN. Antigen attached to the solid phase was detected with enzyme-coupled IgG antibody to Toxoplasma gondii. Neither hepatitis B surface antigen nor antigen of Mycoplasma pneumoniae, rubella, cytomegalovirus or herpes simplex virus interfered with this ELISA. Soluble antigen was detected in 13 (30%) of 42 IgM-positive acute-phase toxoplasmosis patients and in only one of 20 sera cleared of IgM. None of an additional 44 IgM-negative patients with low IgG titres had a positive result in the antigen ELISA. Follow-up studies in four acute-phase toxoplasmosis patients showed that the soluble antigen cleared in all cases before the specific IgM antibodies. Simultaneous detection of IgM antibodies to Toxoplasma gondii and soluble antigen would thus seem to indicate an early stage of the infection.