['Interleukin (IL)-6 regulates various aspects of the immune response. In the context of heart diseases, it has been recognized as a prognostic factor for dilated cardiomyopathy, which often results from myocarditis.', 'Using IL-6-deficient mice, we studied the role of IL-6 in a model of autoimmune myocarditis resulting from immunization with a peptide derived from cardiac alpha-myosin. Prevalence and severity of myocarditis were markedly reduced in the absence of IL-6. CD4+ T cells from immunized IL-6-deficient mice proliferated poorly on restimulation with specific antigen in vitro and did not mediate disease on adoptive transfer into IL-6-competent RAG-2-deficient mice, which otherwise lack B cells and T cells. Production of complement C3, a crucial factor for the development of myocarditis, was strongly upregulated in IL-6+/+ but not in IL-6-deficient mice after immunization.'] Do interleukin-6-deficient mice resist development of autoimmune myocarditis associated with impaired upregulation of complement C3?