Endotoxins

Pfeiffer R, 1894

Lipopolysaccharides (LPS), which form an integral part of the outer membrane of the cell envelope of Gram-negative bacteria

Lipopolysaccharides are important virulence factors once they have entered the body. They cause toxic and pyrogenic effects (exogenous pyrogens). They also influence natural immunity, especially by activating the complement and coagulation systems.

Lipopolysaccharides are recognised and bound by LPS receptors on macrophages. They induce a strong activation of these cells, stimulate the production of cytokines (interferon-alpha, interleukin-6, interleukin-1), which in turn are endogenous pyrogens.

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 strongly resembles MHC-1 complexes.

Furthermore, LPS possess mitogenic activity for B-lymphocytes and induce the formation of antibodies. High LPS concentrations, as they occur during sepsis, lead to endotoxin shock (septic shock).