Vaccination protects B cell-deficient mice against an oral challenge with mildly virulent Toxoplasma gondii.

Prior studies have demonstrated that B cells are important components of protection in vaccinated mice challenged intraperitoneally with a highly virulent type I strain of Toxoplasma gondii parasites. However, it is not known whether B cells are required for vaccinated mice to successfully resist a more physiologically relevant challenge infection with a mildly virulent type II strain of T. gondii. To investigate that question, we vaccinated B cell-deficient C57BL/6 (microMT) mice with an attenuated strain of T. gondii and challenged them with a potentially lethal oral dose of type II T. gondii cysts. Vaccinated microMT mice survived the challenge as well as vaccinated B6 controls, controlled parasites equally well in critical tissues, produced equivalent levels of mRNA for several type 1 cytokines, and exhibited comparably mild histopathology. Thus, a vaccine can protect against infection with a mildly virulent type II strain of T. gondii in the absence of a B cell-dependent immune response.