Selective suppression of tumour-immune cytolytic T lymphocytes in mice with chronic Trypanosoma cruzi infections.
Trypanosoma cruzi is the causative agent of Chagas' disease in man, often leading to suppression of T lymphocyte functions; the present study thus considered the effects of infection by T. cruzi on T-dependent immune responses in a murine model, namely, the immune resistance to a syngeneic tumour and a delayed-type hypersensitivity reaction to sheep red blood cells (SRBC). In BALB.B mice infected with T. cruzi, the graft of syngeneic Gross murine leukaemia virus-induced tumour cells leads to an increased incidence of progressive subcutaneous tumours and development of lymphatic leukaemia. This decreased resistance to tumours correlates with a suppression of the generation of tumour-specific cytolytic T lymphocytes (CTL) from the pre-CTL stage. In contrast, clonal expansion and circulation of T cells detected through their ability to locally transfer a delayed-type hypersensitivity (DTH) reaction to SRBC remained normal in T. cruzi-infected mice. However, at the site of the DTH reaction, a decreased availability of phagocytes was observed in T. cruzi-infected mice.