RESUMO
The spleen plays an important role in cellular immunity leading to parasite elimination, especially in hemo-protozoan parasite infection. In the present study, we quantified the serum IFN-gamma in splenectomized (SP) and non-splenectomized (NSP) cows infected with Theirelia sergenti (TS) to investigate whether the spleen plays a role in the Th1-type cytokine responses in cows following parasite infection. A transient increase in IFN-gamma was observed in the early stages of infection in the NSP cows, and the cows did not develop parasitemia. In contrast, the SP cows showed no IFN-gamma response at the early stage of infection, and the cows developed parasitemia following anemia. The NSP cows produced IgG1 and IgG2 antibodies to TS-specific, whereas the SP cows showed increases only in IgG1. Increased PBMC proliferation by cocanavalin A stimulation was observed concomitant with the IFN-gamma response. Pretreatment with IFN-gamma suppressed the propagation of TS in the SP cattle. These results suggest that the spleen plays an important role in the resistance to TS infection, leading to a Th1-type immune response. IFN-gamma might contribute to the activation of immunocytes and play an important role in the immune response to resist TS proliferation.