Enzyme-linked immunosorbent assay (ELISA) using antibody class capture for the detection of antitoxoplasma IgM.

Sera from 180 patients with suspected toxoplasmic lymphadenopathy were examined for antitoxoplasma IgM by an enzyme-linked immunosorbent assay (ELISA), using antibody class capture (ACCA). Of 82 positive ACCA results, 78 were confirmed by testing the IgM fractions of the sera, obtained by sucrose density gradient centrifugation (SDGC). The four positive results which could not be confirmed were all from patients with at least a year's history of lymphadenopathy. Sera from 10 patients with low Sabin Feldman dye test (DT) titers gave positive ACCA results and subsequent specimens from them showed a rise in antibody concentration, confirming the diagnosis of acute toxoplasmosis. The antitoxoplasma IgM immunofluorescent antibody test (IgM-IFA) on whole serum was relatively insensitive and gave false-positive results with sera containing rheumatoid factor (RF) and antinuclear factor (ANF). There were no false-positive ACCA results with such sera, probably because the conjugates were prepared from F(ab')2 fragments of antitoxoplasma serum. The ACCA proved to be sensitive, specific and easily automated enabling examination of large numbers of specimens.