This lack of a robust IgG response to a parasite specific antigen (CRP) in Balb/c mice during experimental infection with T. cruzi was not due to an inherent inability to generate a response to this T. cruzi antigen, as evident by the magnitude of the IgG response to CRP after genetic immunization in Balb/c versus C57Bl/6 mice. The gene discussed is CRP; the disease is infection.