Correlation between Trypanosoma cruzi parasitism and myocardial inflammatory infiltrate in human chronic chagasic myocarditis: Light microscopy and immunohistochemical findings.

Trypanosoma cruzi parasites are only rarely identified in conventional histological sections of hearts from chronic chagasic patients. This finding suggests that T. cruzi plays no important direct role in the chronic myocarditis that accordingly has been considered mainly an autoimmune process. We reinvestigated this issue using a polyclonal anti-T. cruzi antibody serum to map immunohistochemically the T. cruzi antigen(s) in 9 different regions of 8 necropsy hearts and 24 septal fragments from 24 hearts from chronic chagasic patients. T. cruzi antigen(s) were identified in 7 (87%) of the 8 mapped hearts and in 14 (58%) of the 24 septal fragments. There was a statistically significant correlation between the presence of T. cruzi antigen(s) and moderate or severe inflammatory infiltrate (p = 0.005). When staining revealed amastigotes within intact myocardial fibers, there was no surrounding inflammatory infiltrate. However, when T. cruzi antigen(s) were found in macrophages either as amastigotes, diffusely in the macrophages cytoplasm, or free in the interstitium as round structures similar to amastigotes, there was a heavy inflammatory infiltrate. In the case in which no parasite was detected, a mild inflammatory infiltrate was present in the myocardium. Foci of fibrosis did not stain for T. cruzi antigen. These findings do not exclude a role of autoimmunity in chronic chagasic cardiopathy. However, the striking correlation between the presence of T. cruzi antigen(s) with the severity of site of the inflammatory infiltrate supports a direct role for the parasite in the perpetuation of myocardial inflammation in Chagas' disease. The destruction of microvessels and occasional endothelial cells with parasitism among dense inflammatory infiltrate favors the concept that microcirculatory injury, induced by T. cruzi, also contributes to the lesions of chronic Chagas' disease.