Changes in the proportion and number of monocytes in the peripheral blood of calves infected with Theileria sergenti

The role of IFN-γ in cattle infected with Theirelia sergenti

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.

Mitogenic stimulation of bovine peripheral blood mononuclear cells by Theileria sergenti antigen and inhibition by antibody from experimentally infected cattle

Stimulation with a lysate of Theileria sergenti-parasitized red blood cells (PRBC) resulted in marked proliferation of normal bovine peripheral blood mononuclear cells (PBMC) in vitro. Partial inhibition of the proliferation was demonstrated by the addition of immunoglobulin (Ig) obtained from experimentally infected cattle when they revealed high levels of parasitemia and antibody titres. A mouse monoclonal antibody recognizing a 32 kDa antigen also showed inhibitory activity against the in vitro proliferation of bovine PBMC, but complete inhibition could not be achieved.

In vitro activation of mouse spleen cells by a lysate of Theileria sergenti-infected bovine red blood cells

A lysate of Theileria sergenti-infected bovine red blood cells induced in vitro proliferation of mouse spleen cells in a 2-3-day incubation period. Experiments using B or T cell-enriched preparations showed that a B cell (B220+ CD3- population) was responsible for this non-specific proliferation. In the culture supernatant of spleen cells stimulated with the lysate, considerable amounts of interleukin 2 (IL-2) and gamma-interferon (IFN-gamma) were revealed after 2 days, followed by production of immunoglobulin with a peak at 4-6 days. Thus, it was suggested that a lysate antigen(s) of T. sergenti-infected red blood cells was able to stimulate mouse spleen cells to produce IL-2 and IFN-gamma, which in turn induced the proliferation of B cells and production of immunoglobulin.

Serum from Theileria sergenti-infected cattle accelerates the clearance of bovine erythrocytes in SCID mice

Anemia is a major clinical sign of Japanese bovine theileriosis caused by Theileria sergenti. To investigate the possible factors causing anemia in cattle, we developed a clearance test for bovine erythrocytes (Bo-RBC) in severe combined immunodeficient (SCID) mice. Clearance of Bo-RBC in the SCID mice was significantly accelerated when the mice were inoculated with a serum sample obtained from an infected calf during a highly parasitized phase but not when they were injected with a serum sample obtained during the convalescence phase. Acceleration of the clearance of Bo-RBC was also observed in mice treated with merozoite extract. Furthermore, the clearance of Bo-RBC that had been treated with merozoite extract was accelerated. A significant hemolytic activity in infected serum (highly parasitized phase) was observed. Activities sufficient to accelerate the clearance of Bo-RBC in SCID mice and to induce in vitro hemolysis of Bo-RBC were also observed with a merozoite extract from T. sergenti. The results suggest a possible linkage between the in vitro hemolysis of Bo-RBC and the acceleration of Bo-RBC clearance in SCID mice.