Immune suppression to Trypanosoma cruzi antigens is associated with infection but not immunisation.

Immune responses to Trypanosoma cruzi antigens in infected (C57BL/6 X C3H)F1 hybrid mice were followed throughout the acute infection and into the chronic phase, and compared to immune response kinetics of immunised, but uninfected, mice of the same strain. Anti T. cruzi antibody was detected by day 10 in infected animals and by day 5 in antigen sensitised mice. Animals sensitised with T. cruzi antigens showed strong delayed type hypersensitivity (DTH) responses to T. cruzi antigens. Infected animals were non-responsive during acute infection and immediately after resolution of parasitaemia, but showed similar responses to immunised animals during the chronic phase. The cell mediated immune response to T. cruzi antigens was assessed in vitro lymphocyte transformation tests. Antigen-sensitised mice were responsive to antigen at all time points. Infected animals showed reduced responses during acute infection but attained levels similar to antigen-sensitised mice around 60 days post infection. The results suggest immune suppression during the acute phase is related to infection, but that, unlike other trypanosome infections, suppressor cell-inducing antigens are not present in the T. cruzi antigen preparations tested.