The Toll-like receptor (TLR) family in mammal comprises a family of transmembrane proteins characterized by multiple copies of leucine rich repeats in the extracellular domain and IL-1 receptor motif in the cytoplasmic domain. Like its 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). Ten human homologs of TLRs (TLR1-10) have been described (3). Among this family of receptors, TLR2 and TLR4 have been most studied. These studies have suggested that TLR2 and TLR4 may serve as potential main mediators of LPS signaling (4,5). The TLR4 cDNA codes for a protein consisting of 799 amino acids with approximate molecular weight of 88 kDa (6).
1. Muzio M, Natoli G, Saccani S, Levrero M, and Mantovani A. J. Exp. Med. 187: 2097-2101 (1998).
2. Medzhitov R and Janeway CA. Cell 91: 295-298 (1997).
3. Chuang TH and Ulevitch RJ. Biochim. Biophys. Acta 1518 (1-2): 157-161 (2001).
4. Takeuchi O., Hoshino K, Kawai T, Sanjo H, Takada H, Ogawa K, Takeda K and Akira S. Immunity 11: 443 (1999).
5. Poltorak A, Riccardi-Castagnoli P, Citterio S, and Butler B. Proc. Natl. Acad. Sci USA 97: 2163-2167 (2000).
6. Medzhitov R, Preston-Hurlburt P and Janeway CA Jr. Nature 388 (6640), 394-397 (1997).
7. Akashi S, Ogata H, Kirikae F, Kirikae T, Kawasaki K, Nishijima M, Shimazu R, Nagai Y, Fukudome K, Kimoto M, Miyake K. Biochem Biophys Res Commun. 268(1):172-177 (2000).
8. Shimazu, R., et al. MD-2, a Molecule that Confers Lipopolysaccharide Responsiveness on Toll-like Receptor 4. J. Exp. Med. 189(11): 1777-1782.
9. Paik YH, Schwabe RF, Bataller R, Russo MP, Jobin C, Brenner DA. Hepatology. 2003 May;37(5):1043-55.