On evasion of Trypanosoma cruzi from the host immune response. Lymphoproliferative responses to trypanosomal antigens during acute and chronic experimental Chagas' disease.

The ability of spleen cells taken from mice infected with Trypanosoma cruzi to proliferate after stimulation with specific trypanosomal antigens was investigated during the acute and chronic phases of the disease. Lymphoproliferation was minimal or undetectable during the acute period whereas the chronic phase was characterized by significant responses over a wide range of antigen concentration. Transfer of infected mouse spleen cells to cultures of splenocytes from chronically infected animals failed to modify the response of the latter to antigenic stimulation as measured by DNA synthesis. Furthermore, the responses of infected mouse spleen cells collected during the acute period and freed of Lyt 2.1-bearing lymphocytes, a subclass known to contain the suppressor T cells, did not differ significantly from those of untreated aliquots of the same cell suspensions. These results, together with the fact that the T-cell compartment of the spleen was severely depleted during the acute but not the chronic stage of the infection, suggest that the impaired immunological responsiveness of acutely infected mice may be due in part to the absence or marked reduction of responder and/or accessory T lymphocytes. An active role for suppressor T cells in the reduced response to trypanosomal antigens by lymphocytes from mice in the early, acute phase of T. cruzi infection is not supported by the present observations.