Chemical structure and immunobiological activity of lipid A from Serratia marcescens LPS

Abstract

The chemical structure and immunobiological activities of Serratia marcescens lipid A, an active centre of LPS, were investigated. LPS preparations of S. marcescens were extracted using a hot phenol/water method, after which purified lipid A specimens were prepared by weak acid hydrolysis, followed by normal phase and gel filtration chromatographic separation. The lipid A structure was determined by MS to be a diglucosamine backbone with diphosphates and five C(14) normal chain acyl groups, including two acyloxyacyl groups at the 2 and 3 positions of the non-reducing side. S. marcescens lipid A and Escherichia coli-type synthetic lipid A (compound 506) exhibited definite reactivity in Limulus amoebocyte lysate assays. The lethal toxicity of S. marcescens lipid A was nearly comparable to that of compound 506, and both induced nuclear factor-kappaB activation in murine cells via Toll-like receptor (TLR)4/MD-2 but not TLR2, as well as various inflammatory cytokines in peritoneal macrophages of C3H/HeN mice but not C3H/HeJ mice. Furthermore, S. marcescens lipid A induced nearly the same amounts of tumour necrosis factor alpha, interleukin-6, and nitric oxide production by the murine alveolar macrophage cell line MH-S as compared with compound 506. These results indicate that S. marcescens possesses a penta-acylated lipid A, which is nearly identical to E. coli lipid A in regard to biological activities, while it also may be a crucial virulence factor of the bacterium.