Serological reactivity against cyst and tachyzoite antigens of Toxoplasma gondii determined by FAST-ELISA.

AIMS To obtain quantitative data on the human serological response to Toxoplasma gondii tachyzoite and bradyzoite antigens. METHODS Serum samples from 30 patients who had positive antibody titres against T gondii and from 14 who were seronegative, together with sequential serum samples from four infected individuals, were screened by FAST-ELISA. RESULTS Serum samples from the 30 seropositive patients showed high IgG and IgM titres against the T gondii tachyzoite antigen but very low responses to cyst antigen. This result was borne out in sequential serum samples from patients with toxoplasmosis. CONCLUSION Antibody recognition of the cystic stage of T gondii is low, implying that either this stage is poorly immunogenic or that the antigen load is low.