Toll-like receptor 4 (TLR4) is a member of the toll-like receptor (TLR) family and highly conserved receptors that recognize conserved pathogen-associated molecular patterns (PAMPs). TLR4 is expressed on the cell surface on both hematopoietic and nonhematopoietic cells, including endothelial cells], cardiac myocytes, and cells of the central nervous system (CNS). TLR4 has been regarded as the sensing receptor for gram-negative lipopolysaccharide (LPS). Further research indicated that TLR4also binds endogenous molecules produced as a result of tissue injury. Thus, TLR4 represents a key receptor on which both infectious and noninfectious stimuli converge to induce a proinflammatory response.