Ricerc@Sapienza

he search for novel lipid A analogues from anybiological source that can act as antagonists, displaying in-hibitory activity towards the production of pro-inflammatorycytokines, or as immunomodulators in mammals, is a verytopical issue. To this aim, the structure and immunologicalproperties of the lipopolysaccharide lipid A from the purplenonsulfur bacterium Rhodopseudomonas palustris strainBisA53 have been determined. This lipid A displays a uniquestructural feature, with a non-phosphorylated skeleton madeup of the tetrasacchari de Manp-a-(1!4)-GlcpN3N-b-1!6-GlcpN3N-a-(1!1)-a-GalpA, and four primary amide-linked14:0(3-OH) and, as secondary O-acyl substituents, a 16:0 andthe very long-chain fatty acid 26:0(25-OAc), appended onthe GlcpN3N units. This lipid A architecture is definitely rare,so far identified only in the genus Bradyrhizobium. Immuno-logical tests on both murine bone-marro w-derived andhuman monocyte-derived macrophages revealed an ex-tremely low immunostimulant capability of this LPS lipid A.