Immunological response of Swiss mice to infection with three different strains of Trypanosoma cruzi.

The immunological response of Swiss mice to infection with three strains of Trypanosoma cruzi which differ in their morphobiological, antigenic and isoenzymic characters [Peruvian, 12 SF (São Felipe) and Colombian strains] was investigated. The three strains stimulated an elevation of the immunoglobulin fractions IgG2a, IgG2b and IgM during acute infection, as measured by radial immunodiffusion, and an early drop of IgG1 levels. There were low levels of specific antibodies and a negative cutaneous delayed hypersensitivity test to T. cruzi antigens. Cellular reaction of the spleen was evident, with proliferation of lymphocytes and the presence of blastic lymphoid cells in the red and white pulp, and hyperplasia of germinal centres of the lymphoid follicles. Those aspects were consistent with a depletion of the T-cell zone (periarteriolar lymphocyte sheath). Despite these common features, there were clear differences in the onset, intensity and evolution of the splenic cellular reaction and IgG serum levels and in the relationship between these levels and parasitaemia in the mice infected with the three strains of T. cruzi. A positive correlation was seen between high IgG levels and mortality, corresponding to intense exudative tissue lesions, showing that a raised immunoglobulin level was not associated with protection. It is worth observing that the 12 SF strain, which showed the lowest parasitaemic profile and mortality rate, stimulated the greatest elevation of IgG2b during acute infection; and also that IgG2a and IgG2b were the immunoglobulins which showed the greatest increases following infection by all three strains of T. cruzi.