Trypanosoma cruzi infection in humans and experimental animals often results in a chronic heart and gut inflammation and a dysfunction known as Chagas' disease. Previous studies have shown that the cellular infiltrate in the hearts of animals with chronic Chagas' disease consists mainly of CD8+ T cells. In this study, we have used immunohistochemical techniques to further characterize the immunological nature of chagasic heart lesions in three murine models of experimental Chagas' disease. Double-staining immunohistochemistry revealed that 10-30% of the infiltrating CD8+ T cells in the hearts of infected mice expressed the activation molecules, IL-2 receptor and CD44. In addition, large numbers of cells producing TNF-alpha, TGF-beta, IL-1 alpha, and IL-6 were consistently observed in the heart lesions, appearing during the acute infection and persisting throughout the chronic stage of infection (> 300 days). In contrast, IFN-gamma- and IL-10-producing cells were detected in relatively low numbers and only transiently between approximately 3 and 9 weeks postinfection. Cells producing IL-2, IL-4, and IL-5 were not observed in the hearts of mice at any point during the infection. The appearance of cytokine-producing cells in the hearts correlated with an increased local expression of class I and class II MHC molecules and adhesion molecules (ICAM-1, LFA-1, VLA-4, and VCAM-1). The results of this study suggest that the chronic inflammation in chagasic hearts is highly active and associated with a stable immunological pattern extending from the early acute stage of the infection through the late chronic stage. The pattern of cytokine production in heart is distinct from that observed in lymphoid organs and is not suggestive of an association between particular classes of cytokines and disease development. Instead it appears that both inflammatory and anti-inflammatory cytokines determine the pattern of the cellular response and the severity of disease in T. cruzi infection.