lipopolysackarid

Lipopolysaccharide, often abbreviated as LPS, is a complex molecule found in the outer membrane of Gram-negative bacteria. It is a major component of the bacterial cell wall and plays a crucial role in the structural integrity of these microorganisms. LPS is composed of three distinct regions: lipid A, a core oligosaccharide, and the O-antigen. Lipid A is the hydrophobic anchor that embeds LPS within the bacterial membrane. The core oligosaccharide links lipid A to the O-antigen, and its structure can vary between different bacterial species. The O-antigen is a long, repeating polysaccharide chain that extends from the bacterial surface and is highly variable, contributing to the serological diversity of bacteria.

LPS is a potent immunostimulant. When Gram-negative bacteria infect a host, LPS is released and recognized by the immune system, primarily through Toll-like receptor 4 (TLR4). This recognition triggers a cascade of immune responses, which can include the release of pro-inflammatory cytokines. While this response is essential for clearing bacterial infections, excessive or dysregulated LPS signaling can lead to harmful inflammation, such as in the case of sepsis. The O-antigen portion of LPS is often a target for antibodies, and its variability is a key factor in how bacteria evade the host immune system.