Trypanosoma cruzi: Peripheral blood monocytes and heart macrophages in theresistance to acute experimental infection in rats

The contribution of mononuclear phagocytes to host resistance against acute Chagas disease has been studied in vivo in a rat model inoculated with Try panosoma cruzi, Y strain. Acute T. cruzi infection triggered a dramatic inc rease (937%) in peripheral blood monocyte number at day 12 of infection. At this point, histological analysis of the heart showed high parasitism and diffuse and a moderate to intense mononuclear inflammatory process. Ultrast ructural study revealed a large number of macrophages, in addition to lymph ocytes and undifferentiated cells. Clusters of macrophages exhibited differ ent morphological phenotypes, with evident signs of activation (increase in size, surface rufflings, and amount of cytoplasmic organelles). Cell-to-ce ll contacts involving macrophages and lymphocytes or macrophages and monocy tes were observed. Depletion of macrophages by treatment with silica, a sel ective cytotoxic agent for these cells, caused a significant increase in th e number of amastigote nests in cardiomyocytes. The present findings indica te that the early phase of infection with T. cruzi induces rapid production , maturation, and activation of the monocyte/macrophage system so as to con trol T. cruzi replication, emphasizing the crucial role for macrophages in the rat resistance to Chagas disease. (C) 2001 Academic Press.