lipopolysackarider

Lipopolysaccharide, commonly abbreviated LPS, is a large molecule embedded in the outer membrane of many Gram-negative bacteria. The term lipopolysackarider is a frequent misspelling, but the correct designation is lipopolysaccharide.

LPS consists of three components: lipid A, which anchors the molecule in the membrane and carries endotoxin activity; a core oligosaccharide; and the O-antigen, a variable polysaccharide chain that determines serotype. Lipid A is the primary mediator of toxicity, while the core and O-antigen influence immune recognition and bacterial diversity.

Biogenesis and distribution: LPS is synthesized at the inner membrane and transported to the outer membrane by dedicated machinery. It is relatively stable but can be shed or released during bacterial growth or cell lysis, contributing to inflammation in the host.

Role in immunity and disease: LPS is detected by the host’s Toll-like receptor 4 (TLR4) in complex with the MD-2 co-receptor, triggering signaling pathways that lead to the production of pro-inflammatory cytokines. In severe infections, excessive LPS signaling can cause systemic inflammation, septic shock, and coagulopathies.

Clinical and research relevance: LPS serves as a model endotoxin in immunology and vaccine research and is a routine reference in studies of innate immunity. It is also a critical contaminant to monitor in pharmaceuticals and laboratory reagents. Detection methods include the Limulus amebocyte lysate (LAL) assay and recombinant factor C assays to ensure product safety and experimental integrity.