Attenuation of Trypanosoma brucei is associated with reduced immunosuppression and concomitant production of Th2 lymphokines.

Mechanisms regulating resistance to African trypanosomes were addressed by comparing the immune responses of mice infected with attenuated Trypanosoma brucei brucei lacking the phospholipase C gene (PLC-/-) and those of mice infected with wild-type (WT) parasites. Inhibition of concanavalin A (ConA)-induced T cell proliferation occurred in spleen and lymph nodes of PLC-/-- and WT-infected mice. Although suppressive cells were elicited in spleen and lymph nodes of WT-infected animals, such cells were not detected in lymph nodes of PLC-/--infected mice. PLC-/--infected mice had more interleukin-4 and -10 in their blood than did WT-infected mice. Correspondingly, PLC-/--infected mice had higher IgG1 antibody levels against variant surface glycoprotein than did WT-infected mice. These data indicate that attenuation of T. b. brucei correlates with the absence of cells suppressing ConA-induced T cell proliferation in the lymph nodes, with increased production of Th2 cytokines and a stronger IgG1 antibody response to trypanosome antigens.