The Role of Toll-Like Receptors and Type I Interferons in Host Responses to Bacteria

A number of both secreted, transmembrane receptor proteins and intracellular receptors are involved in recognition of conserved pathogen-associated molecular patterns (PAMPs) on microorganisms. Toll-like receptors (TLRs) are a group of these pathogen-sensing receptors and are important mediators of pathogen-initiated inflammatory signals in inflammatory cells. In recent years it has been understood that TLRs have a role in mediating interferon (IFN) responses. Even though it is clear that IFNs regulate inflammatory responses induced by viruses, at present it is unclear how type I IFNs act in antibacterial defenses. Traditionally, type I IFNs have been considered to have only a minor role in antibacterial host defenses. Recently, however, PAMPs, including lipopolysaccharides (LPSs) and prokaryotic DNA, were found to activate distinctive signal transduction pathways that merge, after pathogen recognition, with those activated by viruses, resulting in high-level type I IFN production. However, our understanding of the role of IFNs in human bacterial diseases is limited. In this review, we will discuss the recent progress made in elucidating the TLR-dependent mechanisms of type I IFN production and their responses during bacterial challenge.