IMMUNOSUPPRESSION IN TRYPANOTOLERANT NDAMA CATTLE FOLLOWING TRYPANOSOMA-CONGOLENSE INFECTION

Tsetse-transmitted Trypanosoma congolense infection causes an impairme nt of in vitro T cell proliferative responses in Boran (Bos indicus) c attle. To assess the importance of this phenomenon as it may relate to the ability of trypanotolerant cattle to control infection with trypa nosomes, T cell proliferative responses to mitogenic stimulus with Con canavalin A were measured in N'Dama (Bos taurus) cattle throughout inf ection. The responses of peripheral blood mononuclear cells from Boran and N'Dama cattle were similar. Depressed proliferative responses wer e observed with cells of both breeds at 12 days post infection, after which the responses returned to levels similar to those recorded pre-i nfection. Immunosuppression was also studied in the lymph nodes of a m ajor histocompatibility complex (MHC)-matched pair of N'Dama cattle. L ymph node cells from the infected animal failed to respond to mitogeni c stimulus. Co-culture experiments in which the cells from this node w ere mixed with either lymph node cells or peripheral blood mononuclear cells from the non-infected MHC-compatible animal revealed the presen ce of suppressor cells, acting in a prostaglandin-independent manner, capable of arresting mitogen-induced T cell proliferation.