Toll-like receptor 3 (TLR3) is a 103kDa (predicted, unglycosylated) type I transmembrane glycoprotein and member of the Toll-like receptor family. It is localized to the endoplasmic reticulum membrane and endosome, and is expressed at high levels in the placenta and pancreas. It is also detected in the dendritic subpopulation of leukocytes. Human TLR3 is synthesized as a precursor with a 23aa signal sequence, a 681aa luminal region, a 21aa transmembrane region, and a 179aa cytoplasmic region. The luminal region contains 23 canonical and two irregular leucine-rich repeats (LRR), 15 N-linked glycosylation sites, and a Toll/IL-1 receptor (TIR) domain (aa758-896). Human TLR3 shares 83% and 80% aa sequence identity with bovine and mouse TLR3, respectively. TLR3 is involved in the innate immune response to microbial agents.