CCL3/Macrophage Inflammatory Protein-1α Is Dually Involved in Parasite Persistence and Induction of a TNF- and IFNγ-Enriched Inflammatory Milieu in Trypanosoma cruzi-Induced Chronic Cardiomyopathy

Abstract

CCL3, a member of the CC-chemokine family, has been associated with macrophage recruitment to heart tissue and parasite control in the acute infection of mouse with <i>Trypanosoma cruzi</i>, the causative agent of Chagas disease. Here, we approached the participation of CCL3 in chronic chagasic cardiomyopathy (CCC), the main clinical form of Chagas disease. We induced CCC in C57BL/6 (<i>ccl</i>3^+/+) and CCL3-deficient (<i>ccl</i>3^-/-) mice by infection with the Colombian Type I strain. In <i>ccl</i>3^+/+ mice, high levels of CCL3 mRNA and protein were detected in the heart tissue during the acute and chronic infection. Survival was not affected by CCL3 deficiency. In comparison with <i>ccl</i>3^+/+, chronically infected <i>ccl</i>3^-/- mice presented reduced cardiac parasitism and inflammation due to CD8⁺ cells and macrophages. Leukocytosis was decreased in infected <i>ccl</i>3^-/- mice, paralleling the accumulation of CD8⁺ T cells devoid of activated CCR5⁺ LFA-1⁺ cells in the spleen. Further, <i>T. cruzi</i>-infected <i>ccl</i>3^-/-mice presented reduced frequency of interferon-gamma (IFNγ)⁺ cells and numbers of parasite-specific IFNγ-producing cells, while the <i>T. cruzi</i> antigen-specific cytotoxic activity was increased. Stimulation of CCL3-deficient macrophages with IFNγ improved parasite control, in a milieu with reduced nitric oxide (NO_x) and tumor necrosis factor (TNF), but similar interleukin-10 (IL-10), concentrations. In comparison with chronically <i>T. cruzi</i>-infected <i>ccl</i>3^+/+ counterparts, <i>ccl</i>3^-/- mice did not show enlarged heart, loss of left ventricular ejection fraction, QTc prolongation and elevated CK-MB activity. Compared with <i>ccl</i>3^+/+, infected <i>ccl</i>3^-/- mice showed reduced concentrations of TNF, while IL-10 levels were not affected, in the heart milieu. In spleen of <i>ccl</i>3^+/+ NI controls, most of the CD8⁺ T-cells expressing the CCL3 receptors CCR1 or CCR5 were IL-10⁺, while in infected mice these cells were mainly TNF⁺. Lastly, selective blockage of CCR1/CCR5 (Met-RANTES therapy) in chronically infected <i>ccl</i>3^+/+ mice reversed pivotal electrical abnormalities (bradycardia, prolonged PR, and QTc interval), in correlation with reduced TNF and, mainly, CCL3 levels in the heart tissue. Therefore, in the chronic <i>T. cruzi</i> infection CCL3 takes part in parasite persistence and contributes to form a CD8⁺ T-cell and macrophage-enriched cardiac inflammation. Further, increased levels of CCL3 create a scenario with abundant IFNγ and TNF, associated with cardiomyocyte injury, heart dysfunction and QTc prolongation, biomarkers of severity of Chagas' heart disease.