Toxoplasma gondii: reactivity of murine sera against tachyzoite and cyst antigens via FAST-ELISA.

The murine serological response to Toxoplasma gondii tachyzoite and cyst antigens was determined using FAST-ELISA. The serum IgG response to tachyzoite antigen was much stronger than that to cyst antigen. Adsorption of immune sera with tachyzoite antigen sharply reduced the reactivity in ELISA with tachyzoite antigen, but had no effect on the titre against cyst antigen, implying that there is virtually no antigenic overlap between the 2 stages. In sequential sera from infected mice the IgG antibody response against tachyzoites was always higher than the response to cyst antigen, whereas the IgM response to cysts was always higher than that to tachyzoites and remained detectable for at least 11 months.