Anti-Ia treatment modulates specific and polyclonal antibody responses in Trypanosoma cruzi-infected mice

Experimental Chagas' disease—infection of mice with the protozoan parasite Trypanosoma cruzi—has been shown to increase the number of Ia-bearing cells in the spleen and the lymph nodes. The majority of these Ia-positive cells were Ig⁺ and included in the large cell fraction of lymphoid organs from T. cruzi-infected animals indicating that they were activated B cells. These data are consistent with the polyclonal B-cell activation occurring during acute and chronic T. cruzi infection. The levels of secreted natural antibodies, of both IgM and IgG isotypes, were significantly increased in the sera of the infected animals. The present communication demonstrates that in vivo anti-Ia treatment of C3H/HeJ mice infected with the CL strain of T. cruzi suppressed the polyclonal B-cell activation, affecting all the isotypes studied, including IgM, IgG2a and IgG2b, whose levels are predominantly increased during T. cruzi infection. In contrast to the decreased secretion of IgG autoantibodies, the levels of IgM autoantibodies were much less affected. The anti-Ia treatment totally abolished the specific anti-parasite response despite the fact that a pool of Ia-Ig positive cells remained after treatment.