Decreased interleukin-2 responsiveness in leukocytes from Trypanosoma brucei-infected mice.

Immunosuppression with respect to those inducible processes which regulate lymphocyte mitogenesis was examined in experimental trypanosomiasis. Splenic leukocytes from Trypanosoma brucei-infected mice showed a decreased proliferative response to the T-cell mitogen concanavalin A. Activated cells secreted normal levels of the endogenous T-cell proliferative signal interleukin-2 (IL-2) and expressed high-affinity IL-2 receptors. However, the ability of activated cells to proliferate in response to exogenous IL-2 was inhibited. These results indicate an impairment of processes which occur after IL-2-receptor binding during lymphocyte mitogenesis. Furthermore, these data indicate that expression of high-affinity IL-2 receptors does not necessarily correlate with an ability to respond to IL-2.