Inflammatory regulation by TLR3 in acute hepatitis

TLR3 is known to respond to dsRNA from viruses, apoptotic cells, and/or necrotic cells. Dying cells are a rich source of ligands that can activate TLRs, such as TLR3. TLR3 expressed in the liver is likely to be a mediator of innate activation and inflammation in the liver. The importance of this function of TLR3 during acute hepatitis has not previously been fully explored. We used the mouse model of Con A-induced hepatitis and observed a novel role for TLR3 in hepatocyte damage in the absence of an exogenous viral stimulus. Interestingly, TLR3 expression in liver mononuclear cells and sinus endothelial cells was up-regulated after Con A injection and TLR3(-/-) mice were protected from Con A-induced hepatitis. Moreover, splenocytes from TLR3(-/-) mice proliferated less to Con A stimulation in the presence of RNA derived from damaged liver tissue compared with wild-type (WT) mice. To determine the relative contribution of TLR3 expression by hematopoietic cells or nonhematopoietic to liver damage during Con A-induced hepatitis, we generated bone marrow chimeric mice. TLR3(-/-) mice engrafted with WT hematopoietic cells were protected in a similar manner to WT mice reconstituted with TLR3(-/-) bone marrow, indicating that TLR3 signaling in both nonhematopoietic and hematopoietic cells plays an important role in mediating liver damage. In summary, our data suggest that TLR3 signaling is necessary for Con A-induced liver damage in vivo and that TLR3 regulates inflammation and the adaptive T cell immune response in the absence of viral infection.