Bacterial lipopolysaccharide (LPS) is the major structural component of the outer wall of all Gram-negative bacteria and a potent activator of the immune system. LPS is recognized by Toll-like receptor 4 (TLR4) which interacts with three different extracellular proteins: LPS-binding protein (LBP), CD14 and, myeloid differentiation protein 2 (MD-2), to induce a signaling cascade leading to the activation of NF-κB and the production of proinflammatory cytokines.
LPS consists of a polysaccharide region that is anchored in the outer bacterial membrane by a specific carbohydrate lipid moiety termed lipid A.
Lipid A is responsible for the immunostimulatory activity of LPS.
The most active form of lipid A contains six fatty acyl groups and is found in pathogenic bacteria such as Escherichia coli and Salmonella species.
Underacylated lipid A structures, containing four or five fatty acids, induce markedly weaker host defense responses and can inhibit in a dose-dependent manner the strong endotoxic response triggered by hexa-acylated LPS.
InvivoGen provides LPS from various bacteria and monophosphoryl lipid A. HEK-Blue™ TLR4 Cells are used to validate the functionality of these TLR ligands.