ROLE OF CD4(-CELLS IN THE CONTROL OF PRIMARY INFECTION WITH BABESIA-MICROTI IN MICE() T)

The role of T cells for the resolution of acute primary infection with Babesia microti was investigated in the present study. BALB/c mice ex hibited a peak parasitemia of approximately 40% of parasitemia and sub sequently recovered naturally from their primary infection. Nude mice, however, could not resolve primary infection and developed persistent high parasitemia. Mice depleted of CD4(+) T cells with monoclonal ant ibody (mAb) had high parasitemia and failed to control the infection. However, depletion of CD4(+) T cells one week after infection did not affect the course of infection. Depletion of CD8(+) T cells showed no apparent effect on the course of infection. High concentration of IFN- gamma was demonstrated in the culture supernatant of spleen cells from untreated and anti-CD8 mAb treated mice, but not from anti-CD4 mAb tr eated mice. Mice treated with anti-IFN-gamma mAb showed higher peak pa rasitemia and remained above 10% of parasitemia until days 26 after in fection. These results suggest that CD4(+) T cells play an essential r ole in the resolution of B. microti acute primary infection and that I FN-gamma produced by CD4(+) T cells is partially responsible for contr ol of early stage of acute infection with B. microti.