Induction of Protective Immunity by Primed B‐1 Cells in Toxoplasma gondii‐Infected B Cell‐Deficient Mice

We examined the role of B-1 cells in protection against Toxoplasma gondii infection using B cell-deficient mice (μMT mice). We found that primed but not naive B-1 cells from wild-type C57BL/6 mice protected B cell-deficient recipients from challenge infection. All μMT mice transferred with primed B-1 cells survived more than 5 months after T. gondii infection, whereas 100% of μMT mice transferred with naive B-1 cells succumbed by 18 days after infection. Additionally, high expression of both T help (Th) 1- and Th2-type cytokines and a high level of nitric oxide production were observed in T. gondii-infected μMT mice transferred with primed B-1 cells. Thus, it was clearly demonstrated that B-1 cells play an important role in host protection against T. gondii infection in μMT mice.