Toll-like receptor expression and function in airway epithelial cells.

Toll-like receptors (TLRs) belong to a family of transmembrane proteins that can recognize and discriminate a diverse array of microbial antigens. Following their activation by specific ligands, TLRs initiate intracellular signaling cascades that culminate in the activation of transcription factors and ultimately lead to changes in pro-inflammatory gene expression. The TLR family constitutes an important component of the innate immune system and, although most commonly considered to be associated with immune cell responses, TLRs are also known to be functionally expressed on a variety of other cell types. Epithelial cells represent a significant component of the cellular content of the airways. These cells provide both a barrier to infection and an active defense mechanism against invading microbes. The expression and function of TLRs on airway epithelial cells has been an area of increasing interest in the recent past. This review will summarize advances in our understanding of the role of TLRs in airway epithelial cells.