Lipid A

[3] Lipid A consists of two glucosamine (aminosugar) units, in a β(1→6) linkage, with attached acyl chains ("fatty acids"), and normally containing one phosphate group on each carbohydrate.

The enzymes involved in Lipid A synthesis are conserved among Pseudomonas aeruginosa, Escherichia coli, Bordetella bronchiseptica, and Salmonella.

When present in the body at high concentrations during a gram-negative bacterial infection, it may cause shock and death by an "out of control" excessive immune reaction.

Other work has shown that the removal of one or two acyl chains from native lipid A can significantly reduce activation of inflammatory responses.

Pathogenic bacteria may employ LPS with low biological activity of its lipid A to evade proper recognition by the TLR4/MD-2 complex, dampening the host immune response and increasing the risk of bacterial dissemination.

Yet, defining and understanding how even the smallest structural differences between the very similar lipid A species may affect the activation of the immune response may provide the mechanism for the fine tuning of the latter and new insights to immunomodulatory processes.