Toll-like receptor 4-induced cytokine production circumvents protection conferred by TGF-beta in coxsackievirus-mediated autoimmune myocarditis.

Coxsackie B virus (CBV) infections are a leading cause of autoimmune myocarditis associated with inflammatory heart disease and sudden death in young adults. Previously, we demonstrated that transgenic expression of the immunosuppressive cytokine, transforming growth factor-beta (TGF-beta), specifically in the pancreas protected otherwise susceptible mice from CBV-mediated autoimmune myocarditis. Herein, we demonstrate that macrophages from these transgenic mice fail to upregulate the costimulatory molecule CD40 following infection, suggesting that pancreatic TGF-beta protects by limiting antigen stimulation. We further demonstrate that co-administration of LPS from Salmonella minnesota, a Toll-like receptor (TLR)-4 ligand, with CBV infection overcomes protection whereas the TLR-2 agonist, LPS from Porphyromonas gingivalis, does not. Furthermore, LPS-mediated disease induction correlates with increased levels of pro-inflammatory cytokines. Interestingly, the action of LPS (TLR-4) did not alter antibody isotype switching, increase viral replication or modulate CD40 expression. Instead, LPS breaks protection through an alternative mechanism specific to TLR-4 signaling.