Lipopolysaccharides from Different Species with Different Lipid A Structures Induce Toll-Like Receptor 4 Activation and React with Melioidosis Patient Sera.

Lipopolysaccharides (LPSs) of Gram-negative bacteria comprise lipid A, core, and O-polysaccharide (OPS) components. Studies have demonstrated that LPSs isolated from the pathogenic species and and from less-pathogenic species, such as , are potent immune stimulators. The LPS structure of , the causative agent of melioidosis, is highly conserved in isolates from Thailand; however, the LPSs isolated from other, related species have not been characterized to enable understanding of their immune recognition and antigenicities. Here, we describe the structural and immunological characteristics of the LPSs isolated from eight species and compare those for to those for the other seven species. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), gas chromatography (GC), SDS-PAGE, Toll-like receptor 4 (TLR4) stimulation, and immunoblot analysis were performed on these species. MALDI-TOF profiles demonstrated that lipid A contains predominantly penta-acylated species modified with 4-amino-4-deoxy-arabinose residues at both terminal phosphate groups. The lipid A could be differentiated based on mass differences at 1,511, 1,642, 1,773, and 1,926 and on fatty acid composition. LPSs of all species induced TLR4-dependent NF-κB responses; however, while SDS-PAGE analysis showed similar LPS ladder patterns for , , and , these patterns differed from those of other species. Interestingly, immunoblot analysis demonstrated that melioidosis patient sera cross-reacted with OPSs of other species. These findings can be used to better understand the characteristics of LPS in species, and they have implications for serological diagnostics based on the detection of antibodies to OPS.