PARTIAL PROTECTION OF SEVERE COMBINED IMMUNODEFICIENT MICE AGAINST INFECTION WITH BABESIA-MICROTI BY IN VITRO-GENERATED CD4(-CELL CLONES() T)

Because CD4(+) T cells were considered to be involved in protection ag ainst infection with Babesia microti, specific CD4(+) T cells were gen erated in vitro from recovered BALB/c mice and their protective activi ty was tested in vivo. The cells produced varying amounts of interfero n (IFN)-gamma in vitro in response to parasite antigen. In passive tra nsfer experiments, three out of eleven T cell clones tested exerted pr otective activity in the early phase after infection. However, there s eemed to be no correlation between this protection and in vitro IFN-ga mma production by the T cell clones. Although the protection was parti al and short-lived, the result provided direct evidence that CD4(+) T cells play a crucial role in defense against B. microti.