An endotoxin and biologically active component of the Gram-negative bacterial cell wall that is a Toll-like receptor 4 (TLR4) agonist with potential immunostimulatory activity. Upon internalization, lipopolysaccharide (LPS) activates TLR4 which in turn activates the NFkappaB pathway, in addition to mitogen-activated protein kinases signaling pathways. This leads to the release of proinflammatory cytokines and stimulates an innate immune response against vaccine antigens.

Lipid-containing polysaccharides which are endotoxins and important group-specific antigens. They are often derived from the cell wall of gram-negative bacteria and induce immunoglobulin secretion. The lipopolysaccharide molecule consists of three parts: LIPID A, core polysaccharide, and O-specific chains (O ANTIGENS). When derived from Escherichia coli, lipopolysaccharides serve as polyclonal B-cell mitogens commonly used in laboratory immunology. (From Dorland, 28th ed)