A role for CD4+ and CD8+ cells and not for CD25+ cells in the control of Plasmodium bergheiAnka blood stage parasites in rats

In previous studies of the infection of rats by P. bergheiAnka, we have shown that primary blood stage infection induced the expansion of CD4+ T cells and CD8+ T cells in adult resistant rats while the number of CD4+CD25+ cells was found to be higher in young susceptible rats. In this work, the respective contribution of each cell population was determined in young and adult rats treated with monoclonal antibodies. Down-regulation of surface CD25 molecules, including those expressed by CD4+ cells did not significantly enhance the capacity of young rats to control the development of erythrocytic stages or modify the course of infection in adult infected rats. However, we observed a significant loss of protection when adult rats were treated with anti-CD4 mAb (W3/25) with higher blood parasitemia levels and ~ 50% of rats succumbed to infection. More importantly and in contrast to earlier studies performed in mice, we found a significant increase in blood parasite levels and a significant delay in parasite clearance in adult rats treated with anti-CD8 mAb OX8, known to deplete CD8+ cells. These results suggest that CD8+ cells play a critical role in the development of immune responses in rats to control the replication of blood stage parasites.