[1] Structure:

Lipopolysaccharides (LPS) are major components of gram-negative bacteria, densely incorporated into the outermost portions of their cell wall. Because its sugar portion is water-soluble and its lipid portion is oil-soluble, LPS is an amphipathic substance, which is soluble in both water and oil. LPS is normally more easily soluble in water than in oil.

[2] Biological Activity:

The most well-known biological activity of LPS is macrophage activation. Macrophages are cells present throughout the body that play a central role in innate immunity. They protect the body from bacteria and viruses, help repair wounds, and are indispensable in metabolism regulation. Therefore, macrophage-activating LPS enhances protection ability against infection, wound healing, and metabolic control.

[3] Mechanism of LPS-induced Immune Cell Activation:

The mechanism of macrophage activation by LPS is well understood today. The macrophage cell surface contains many receptors designed to detect various substances. Of these receptors, the receptor called TLR4 detects LPS (*1). When LPS binds to TLR4, signals are transmitted to the intracellular nucleus so that nuclear genes are turned on and the cell is activated.

Peptidoglycan from lactic acid bacteria, and β-glucan from mushrooms or yeast bind to another receptor called TLR2, which then activates macrophages. Therefore, yogurt and Agaricus mushroom species also activate macrophages. However, in order to activate macrophages to the same extent, peptidoglycan and β-glucan require 1,000 to 10,000 times the amount of LPS, illustrating how potent the immuno-activation capacity of LPS is.

Discoveries involving innate immunity activation by microbial components, such as LPS, was awarded the 2011 Nobel Prize in Physiology or Medicine.

(*1) Endotoxin recognition molecules, Toll-like receptor 4-MD-2, Seminars in Immunology 16: 11-16 (2004)