TLR4, a type I membrane protein that belongs to the Toll-like receptor family, cooperates with LY96 and CD14 to mediate the innate immune response to bacterial lipopolysaccharide (LPS). It acts via MyD88, TIRAP and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response TLR4 Belongs to the lipopolysaccharide (LPS) receptor, a multi-protein complex containing at least CD14, LY96 and TLR. TLR4 binds to LY96 via the extracellular domain, and to MyD88 and TIRAP via their respective TIR domains. The protein contains 19 leucine-rich (LRR) repeats, and It is highly expressed in heart, spleen, lung and muscle. Lower levels are found in liver and kidney. Interstrain analyses reveal that TLR4 is a polymorphic protein and that the extracellular domain is far more variable than the cytoplasmic domain, which is variable at the C-terminal.