Endotoxin evaluation of eleven lipopolysaccharides by whole blood assay does not always correlate with Limulus amebocyte lysate assay

Lipopolysaccharide (LPS), which makes up about 75% of the surface of Gram-negative bacteria, is known to be their major immune stimulatory principle (for review, see Rietschel and Brade1). It is released from the bacterial surface when bacteria multiply, or when they die and lyse, leading to the activation of immune cells as well as epithelial, endothelial or smooth muscle cells.2 The recognition of LPS by host cells is an important step for the induction of inflammatory processes and antibacterial defense mechanisms, but might also lead to multiorgan failure and shock upon excessive systemic LPS exposure.3–5 Chemical characterization and structural analysis of LPSs from numerous enterobacteriaceae have revealed common structural features. The basic structure of LPS consists of a repetitive polysaccharide (O-antigen), which forms the outer part, the core oligosaccharide and the lipid A moiety, which is embedded in the outer membrane.6–8 The O-antigen carbohydrate chain is a polymer of repeating oligosaccharides, which differ between species and determine the serological specificity of bacteria. In contrast, the structure of the lipid A, which consists of a phosphorylated disaccharide backbone, substituted with fatty acid, is highly conserved and exerts the endotoxic activity.9–11 It is recognized by host immune cells via specific pattern recognition receptors, which immediately activate the host cells and stimulate cytokine release and complement activation leading to inflammatory responses.12 The C3H/HeJ mouse has long been known to be hyporesponsive to LPS