Lipopolysaccharide

Lipopolysaccharide (LPS) is a heat-stable endotoxin from the outer layer of the cell envelope of Gram-negative bacteria. LPS is composed of lipid-A, the core polysaccharide (core) and an O-specific polysaccharide component.

Once it has entered the body, LPS is an important virulence factor. LPS causes toxic and pyrogenic effects (exogenous pyrogens). It also influences natural immunity, particularly by activating the complement and coagulation systems.

Lipopolysaccharides are recognized and bound by LPS receptors on macrophages. LPS is one of the strongest macrophage activators and induces the production of cytokines (interferon-alpha, interleukin-6, interleukin-1).

LPS can be recognized by certain T cells in conjunction with CD1 (lipid antigen-CD1 presentation pathway). CD1 glycoproteins belong to the so-called MHC-like molecules; their structure is strongly reminiscent of MHC-1 complexes.

Furthermore, LPS has a mitogenic activity for B lymphocytes and induces the formation of antibodies. A high LPS concentration, as occurs in sepsis, leads to endotoxin shock (septic shock). Experimentally, LPS produces the Sanarelli-Shwartzman reaction.