Induction of tolerance toToxoplasma gondii in newborn mice by maternal antibody

To develop an animal model for analysing the suppressed immune response toToxoplasma gondii in newborn humans with congenital toxoplasmosis, newborn mice from chronically infected mothers were inoculated intraperitoneally with bradyzoites of an avirulent strain. The newborn mice with maternalToxoplasma antibodies showed a marked delay in the production ofToxoplasma antibodies when infected after birth. Many mice (11/13; 85%) developed a state of tolerance toT. gondii after disappearance of the maternal antibody, demonstrable by the absence ofToxoplasma antibody in their sera despite the fact that they were infected. The duration of tolerance differed between individuals, with two mice showing the longest tolerant state of 8 weeks. This murine model might be suitable for analysing the mechanism of suppressed immune response toT. gondii that has been observed in many human cases of congenital toxoplasmosis.