''Autoimmune rejection'' of neonatal heart transplants in experimental Chagas disease is a parasite-specific response to infected host tissue

Infection with the protozoan parasite Trypanosoma cruzi often results in chronic heart- and gut-associated disease known as Chagas disease. In this study we show that contrary to previous reports, neonatal hearts transplanted into mice chronically infected with T. cruzi do not exhibit signs of autoimmune-type rejection or any significant inflammatory response. In addition to an absence of inflammation, these syngeneic heart transplants survive for more than 1 year and are absolutely free of parasites as determined by in situ PCR analysis. However, if well-established transplanted hearts in chronically infected mice are directly injected with live parasites, a rapid and dramatic inflammatory response ensues that results in cessation of heart function. Likewise, transplanted hearts established in mice prior to systemic infection with T. cruzi or hearts transplanted into mice during the acute stage of T. cruzi infection become parasitized and develop inflammatory foci. In these cases where the transplanted hearts become parasitized, the ensuing inflammatory response is nearly identical to that observed in the native hearts of T. cruzi-infected mice in terms of cell types present and adhesion molecules and cytokines expressed. Importantly, this response is strikingly different from that observed in the allogeneic heart rejection. These results clearly document that parasitization of heart tissue is both necessary and sufficient for the induction of tissue damage in Chagas disease and strongly argue against a principal autoimmune etiology for this disease.