The toll-like receptors (TLRs) in mammals comprise a family of transmembrane proteins characterized by multiple copies of leucine rich repeats in the extracellular domain and an interleukin-1 (IL-1) receptor motif in the cytoplasmic domain. Like their counterparts in Drosophila, TLRs signal through adaptor molecules.1 The TLR family is a phylogenetically conserved mediator of innate immunity that is essential for microbial recognition.2 Most mammalian species have between ten and fifteen types of TLRs. Ten functional TLRs (TLR1-10) have been identified in human. Humans also encode a TLR11 gene but it contains several stop codons and protein is not expressed. However, mouse and rat TLR11 are functional, and it is thought that human TLR11 function was lost during evolution. Historically speaking, TLR expression has been most extensively studied in the immune system. Overall, TLRs are highly expressed in immune competent cells, including macrophages, dendritic cells, neutrophils, mucosal epithelial cells and dermal endothelial cells. However, TLRs have also been identified in many other cell types and anatomical tissue locations where they are expressed either constitutively or induced during infection. TLR3 cDNA codes for a protein with approximate molecular weight of 120 kDa.3 TLR3 has a restricted expression pattern being expressed in dendritic cells (DC).3,4,5 The expression of TLR3 in a single cell type may indicate a specific role for this molecule in a restricted setting.WARNING This product is not for human or veterinary use.
