Endotoxin

Endotoxin, also called lipopolysaccharide (LPS), is the main outer membrane component of Gram-negative bacteria and plays a key role during severe Gram-negative infection, sepsis, and shock. Endotoxins are amphiphilic molecules consisting of a hydrophilic polysaccharide part and a covalently bound hydrophobic lipid component, termed lipid A. The polysaccharide part can be divided into two subdomains, the core region and the O-specific chain, composed of a sequence of repeating units of identical polysaccharides Endotoxins gain access to body fluids and organs by infection and translocation from the gut. It is rather beneficial for the host, lead to enhanced resistance to infections and malignancy due to its immune-stimulatory activity. However, when larger amounts of endotoxins are present in the bloodstream, released endotoxins lead to various pathophysiological reactions including tachypnea, hypotension, fever, disseminated intravascular coagulation, leukopenia, tachycardia, and multiorgan failure.

The harmful, as well as the beneficial host responses to LPS, are not induced directly but rather mediated by immune modulator molecules such as tumor necrosis factor α (TNFα), members of the interleukin family (IL-1, IL-6, IL-8, IL-12), interferon α, reduced oxygen species, and lipids. These mediators are released mainly by monocytes/macrophages, but also other cells like vascular cells, polymorphonuclear cells, and T cells are participating in the response to LPS.