Lipopolysaccharide also known as endotoxins are large molecules made up of lipid and polysaccharide that is found on the outer surface of most gram negative bacteria. LPS is made up of lipid A-core oligosaccharide (OS), and O-specific polysaccharide or O antigen. The biosynthesis of LPS is a multifaceted process involving various steps that occur at the bacterial inner membrane followed by the translocation of LPS molecules to the bacterial cell surface. The lipid A-core OS is assembled independently from the O antigen and both biosynthesis pathways converge by the ligation of the O antigen onto outer core domain of the lipid A-core OS acceptor. LPS are one of the major components of the outer membranes of gram-negative bacteria, providing integrity, and in many cases being the molecule that interacts with surfaces.
The fever-inducing effect of lipopolysaccharides (LPS) is very well know and human blood is extremely responsive to this pyrogen. Upon infection, lipopolysaccharide is associated with toxicity and immunogenicity. Whenever a gram negative bacteria enters the body, the LPS present on the bacterial cell wall acts as a stimulant for the host primary defense mechanism that is the innate immune. Endotoxins, which are an integral part of the gram-negative cell wall, are released on the death of the bacterium and react with CD14 and TLR-4 receptors on the macrophage surface. Intracellular signaling induces the synthesis and release of proinflammatory cytokines (IL-1, IL-2, IL-6, IL-8, and TNF-α [tumor necrosis factor–alpha]).
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