Endotoksin

Endotoksin, or endotoxin, refers to the lipopolysaccharide (LPS) component of the outer membrane of most Gram-negative bacteria. Unlike exotoxins, endotoxins are not actively secreted; they are released when bacteria die, lyse, or shed outer-membrane vesicles. The toxic moiety is lipid A, which anchors the molecule in the membrane and is accompanied by a core polysaccharide and, in many strains, an O-antigen polysaccharide side chain.

Endotoxins trigger host immune responses by binding to LPS-binding protein and presenting to CD14 and the TLR4/MD-2 receptor complex on immune cells. This activates signaling pathways (such as NF-κB) and leads to production of proinflammatory cytokines, including TNF-α, IL-1β, and IL-6. The resulting inflammatory response can cause fever and, in severe cases, septic shock and disseminated intravascular coagulation. Endotoxins are relatively heat-stable compared with many exotoxins.

Clinical relevance: endotoxemia or sepsis can arise from infection with Gram-negative bacteria (e.g., Escherichia coli, Klebsiella, Pseudomonas, Salmonella). Detection in laboratory samples is commonly performed with the Limulus amebocyte lysate (LAL) assay or recombinant alternatives.

Endotoxins differ from exotoxins, which are soluble secreted proteins produced by various bacteria and act on specific cellular targets. Management of endotoxemia focuses on treating the underlying infection and providing supportive care; in some contexts, therapies aimed at neutralizing lipopolysaccharide or modulating the inflammatory response may be considered.