Interleukin 4 is a crucial cytokine in controlling Trypanosoma brucei gambiense infection in mice.

The role of interleukin 4 (IL-4) was studied in relation to host defense during Trypanosoma brucei gambiense IL3253 (IL3253) infection in mice. BALB/c/A-+/+ (BALB/c), BALB/c/A-nu/nu (nude) and C.B-17/Icr-scid/scid (SCID) mice were infected intraperitoneally with 5 x 10(3) bloodstream forms (BSFs) of the trypanosome. The BALB/c mice showed high resistance to IL3253 infection with sporadic parasitemia. The nude mice were also able to control IL3253 infection and experienced low, but persistent parasitemia. However, the SCID mice, which have no functional T- and B-cells, showed high susceptibility to IL3253 infection with more than 1 x 10(8) BSFs/ml. Serum IL-4 levels in the infected BALB/c mice were increased on days 12-18 post-infection (PI). In BALB/c mice depleted of CD4+ T-cells by monoclonal antibody (mAb) treatment, parasitemia was persistent, ranging from 1 x 10(4) to 1 x 10(6) BSFs/ml and was significantly higher than that of the other groups. IL-4 was not detected in the serum of CD4+ T-cells-depleted mice. On the other hand, anti-IL-4-treated IL3253-infected BALB/c mice relapsed significantly longer than the control mice (p < 0.01). These findings suggest that the CD4+ T-cells may control the levels of parasitemia in IL3253 infection through the IL-4 pathway.