Toll-like receptors in antiviral immunity: more than just response

The detection of a viral pathogen by Toll-like receptors (TLRs) is a crucial component of antiviral immunity. However, there is increasing evidence that specific molecules in the TLR pathways might also play an important role in maintaining a proper immune environment and in the prevention of pathological symptoms of disease. This involvement in the pathogenesis of a disorder has been shown for a number of infectious as well as noninfectious conditions. A recent study investigated the role of TLR3, which recognizes double-stranded RNA, in respiratory sVncytial virus (RSV) infection using TLR3(-/-) mice. Although no differences in viral growth were observed, the results demonstrated significant enhancement in mucus production in the airways of RSV-Infected TLR3(-/-) mice, accompanied by an increase in pulmonary T helper 2-type cytokine expression. These findings indicate that TLRs might be integral parts of an appropriate immune environment in addition to their known function in pathogen recognition and subsequent cytokine production.