The immune responses to Trypanosoma cruzi infection of germfree mice were compared to the responses of infected conventional mice. Two groups (40 animals in each group) of 2-month old female CFW germfree and conventional mice were used. The IgM and IgG which bound to the surface of T. cruzi epimastigotes determined by ELISA were significantly lower in germfree than in conventional mice (1/3 and 1/5 for IgM and IgG, respectively). 2. After infection there was a three-fold increase in the circulating levels of these immunoglobulins in germfree but not in conventional mice. Twenty-one days after T. cruzi inoculation, both IgG and IgM levels were similar in germfree and conventional animals. 3. Footpad swelling after T. cruzi-antigen inoculation was initially four-fold more intense in germfree than in conventional mice. 4. These results suggest that the reduced humoral immune response of germfree mice during the initiation of experimental Chagas' disease may be responsible for the more severe parasitism when compared to conventional mice.
