GP 50/55, a membrane antigen of Trypanosoma cruzi involved in autoimmunity and immunosuppression.

Chagas' disease results from the infection of the protozoan parasite Trypanosoma cruzi and affects several million people in South America. Several alterations of the immune response have been described in this disease, such as severe immunosuppression of both cellular and humoral responses and the induction of autoantibodies crossreacting with host cells and tissues. We described here a GPI-linked 50/55 kDa antigen (GP50/55) present on the T. cruzi membrane, but not in the membrane of other parasites of the family Trypanosomatidae. We have obtained several monoclonal antibodies which specifically recognize this molecule. One of these GP50/55-specific mAbs (C10) crossreacts with a 28 kDa antigen expressed on the membrane of activated mouse and human T and B lymphocytes, after "in vitro" activation with mitogens, phorbol esters, or antigen, and on several murine T and B lymphocyte cell lines. Furthermore, this mAb was able to suppress mouse and human T and B cell proliferation to any of those stimuli. In addition, sera from T. cruzi-infected mice or Chagasic patients but not from uninfected mice or control patients contain antibodies which recognize a similar p28 antigen and also suppress the proliferation of human T lymphocytes. These results suggest a possible role of autoantibodies as an alternative mechanism for T. cruzi-associated immunosuppression.