Abstract
The degree of phosphorylation and phosphoethanolaminylation of lipid A on neisserial lipooligosaccharide (LOS), a major cell-surface antigen, can be correlated with inflammatory potential and the ability to induce immune tolerance in vitro. On the oligosaccharide of the LOS, the presence of phosphoethanolamine and sialic acid substituents can be correlated with in vitro serum resistance. In this study, we analyzed the structure of the LOS from 40 invasive isolates and 25 isolates from carriers of Neisseria meningitidis without disease. Invasive strains were classified as groups 1-3 that caused meningitis, septicemia without meningitis, and septicemia with meningitis, respectively. Intact LOS was analyzed by high resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Prominent peaks for lipid A fragment ions with three phosphates and one phosphoethanolamine were detected in all LOS analyzed. LOS from groups 2 and 3 had less abundant ions for highly phosphorylated lipid A forms and induced less TNF-α in THP-1 monocytic cells compared with LOS from group 1. Lipid A from all invasive strains was hexaacylated, whereas lipid A of 6/25 carrier strains was pentaacylated. There were fewer O-acetyl groups and more phosphoethanolamine and sialic acid substitutions on the oligosaccharide from invasive compared with carrier isolates. Bioinformatic and genomic analysis of LOS biosynthetic genes indicated significant skewing to specific alleles, dependent on the disease outcome. Our results suggest that variable LOS structures have multifaceted effects on homeostatic innate immune responses that have critical impact on the pathophysiology of meningococcal infections.
Highlights
The degree of phosphorylation and phosphoethanolaminylation of lipid A on neisserial lipooligosaccharide (LOS), a major cell-surface antigen, can be correlated with inflammatory potential and the ability to induce immune tolerance in vitro
MALDI-TOF mass spectrometry (MS) of Intact LOS from N. meningitidis—The negative-ion MALDI-TOF spectra of intact LOS contained peaks for molecular (M Ϫ H)Ϫ ions and for ions produced by prompt fragmentation occurring in the source that cleaved the labile bond between the non-reducing terminal N-acetylglucosamine moiety on the lipid A moiety and keto3-deoxyoctulosonic acid (Kdo) on the OS moiety (Fig. 1)
We have previously shown that the degree of phosphorylation and phosphoethanolaminylation of lipid A on neisserial LOS can be correlated with inflammatory potential and ability to induce immune tolerance in vitro [1,2,3, 27]
Summary
LOS Structure Correlates with Meningococcal Pathology tion of the LOS occurs during the MS analysis, enabling assignment of proposed compositions for the OS moieties as well as a comparison of the relative ion abundance of the lipid A phosphoforms. Our results show that isolates producing LOS with the most highly inflammatory, most highly phosphorylated lipid A were more restricted to the CNS and had reduced ability to cause septicemia, which is correlated with higher case fatality rates. We found that the OS of the invasive isolates was more highly sialylated and phosphoethanolaminylated than OS from LOS of isolates from those individuals who did not become ill but only carried the bacteria. The results highlight the multifaceted and complex pathogenesis of meningococcal infections that uniquely occur in their human hosts
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