The role of IL-4 has often been studied, especially in the Leishmania major
infection model. but not in Trypanosoma cruzi infection. In the present st
udy, the role of IL-4 in host defense against infection with the Tulahuen s
train of T. cruzi was examined by depleting IL-4 with an anti-IL-gamma mono
clonal antibody in vivo. In both IL-4 depleted and control C57BL/6 mice, th
e parasitemia showed peaks on the 21st day of infection. Both parasitemia a
nd mortality were decreased in IL-4 depleted mice compared with control mic
e when IFN-gamma: and nitric oxide productions were increased in IL-4 deple
ted mice compared with control mice. The mice treated with N-nitro-L-argini
ne methyl ester, a competitive inhibitor of nitric oxide synthase, showed i
ncreased susceptibility to T. cruzi infection to the same level in both IL-
4 depleted and control mice. Thus, it is suggested that endogenous IL-4 ind
uces susceptibility to T. cruzi mainly by suppressing the production of IFN
-gamma and nitric oxide, which has trypanocidal activity.