Partial protection of severe combined immunodeficient mice against infection with Babesia microti by in vitro-generated CD4+ T cell clones.

Because CD4+ T cells were considered to be involved in protection against infection with Babesia microti, specific CD4+ T cells were generated in vitro from recovered BALB/c mice and their protective activity was tested in vivo. The cells produced varying amounts of interferon (IFN)-gamma in vitro in response to parasite antigen. In passive transfer experiments, three out of eleven T cell clones tested exerted protective activity in the early phase after infection. However, there seemed to be no correlation between this protection and in vitro IFN-gamma production by the T cell clones. Although the protection was partial and short-lived, the result provided direct evidence that CD4+ T cells play a crucial role in defense against B. microti.