Murine cytomegalovirus (MCMV) infection of BALB/c mice produces acute and chronic myocarditis similar to clinical disease in humans. In contrast, MCMV-infected C57BL/6 mice develop only mild acute myocarditis. We have investigated the effect of administration of the immunomodulator lipopolysaccharide (LPS) on the development of postviral myocarditis in mice. LPS exacerbated heart inflammation in both strains of MCMV-infected mice, with normally resistant C57BL/6 mice developing chronic myocarditis. Autoantibodies to cardiac myosin were enhanced with LPS treatment in both MCMV-infected mouse strains. LPS treatment also increased the production of TNF in the sera without affecting virus titers in the spleen, liver, or salivary glands, a target organ most affected during persistent virus infection. In LPS/MCMV-infected BALB/c mice, TNF, IL-6, and IL-10 levels were detected in cultures of heart infiltrating cells but not in splenocytes. Importantly, administration of the bioactive synthetic TNF peptide (amino acids 114-130) increased myocarditis in C57BL/6 mice, similar to that seen with LPS treatment. TNF peptide/MCMV-infected BALB/c and C57BL/6 mice showed distinct differences in the expression pattern of IFN-gamma, IL-10, and TNF. These data show that the disease may be partly regulated by TNF among other select cytokines and autoantibodies to cardiac myosin. The immunopathological nature of MCMV-induced myocarditis is thus highlighted. (C) 2001 Elsevier Science.