Human lipooligosaccharide IGG that prevents endemic meningococcal disease recognizes an internal lacto-N-neotetraose structure

Innate immune response to lipooligosaccharide: pivotal regulator of the pathobiology of invasive Neisseria meningitidis infections

Infections due to Neisseria meningitidis afflict more than one million people worldwide annually and cause death or disability in many survivors. The clinical course of invasive infections has been well studied, but our understanding of the cause of differences in patient outcomes has been limited because these are dependent on multiple factors including the response of the host, characteristics of the bacteria and interactions between the host and the bacteria. The meningococcus is a highly inflammatory organism, and the lipooligosaccharide (LOS) on the outer membrane is the most potent inflammatory molecule it expresses due to the interactions of the lipid A moiety of LOS with receptors of the innate immune system. We previously reported that increased phosphorylation of hexaacylated neisserial lipid A is correlated with greater inflammatory potential. Here we postulate that variability in lipid A phosphorylation can tip the balance of innate immune responses towards homeostatic tolerance or proinflammatory signaling that affects adaptive immune responses, causing disease with meningitis only, or septicemia with or without meningitis, respectively. Furthermore, we propose that studies of the relationship between bacterial virulence and gene expression should consider whether genetic variation could affect properties of biosynthetic enzymes resulting in LOS structural differences that alter disease pathobiology.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Opacity proteins of neisseria gonorrhoeae in lipooligosaccharide mutants lost ability to interact with neutrophil-restricted CEACAM3 (CD66d)

Lipooligosacharide (LOS) of Neisseria gonorrhoeae (gonococci, GC) is involved in the interaction of GC with host cells. Deletion of the alpha-oligosaccharide (alpha-OS) moiety of LOS (lgtF mutant) significantly impairs invasion of GC into epithelial cell lines. GC opacity (Opa) proteins, such as OpaI, mediate phagocytosis and stimulate chemiluminescence responses in neutrophils in part through interaction with members of the carcinoembryonic antigen (CEA) family, which includes CEACAM3 (CD66d), a human neutrophil specific receptor for phagocytosis of bacteria. In the present work, we examined the effects of OpaI-expressing lgtF mutant on phagocytosis by HeLa-CEACAM3 cells and chemiluminescence responses in neutrophils. The results showed that lgtF mutant even expressing OpaI completely lost the ability to promote either phagocytosis mediated by CEACAM3 interaction in HeLa cells or chemiluminescence responses in neutrophils. These data indicated that Opa proteins in the lgtF mutant, which might result from the conformational change, cannot be functional.

Analysis of Bacterial Lipooligosaccharides by MALDI-TOF MS with Traveling Wave Ion Mobility

Lipooligosaccharides (LOS) are major microbial virulence factors displayed on the outer membrane of rough-type Gram-negative bacteria. These amphipathic glycolipids are comprised of two domains, a core oligosaccharide linked to a lipid A moiety. Isolated LOS samples are generally heterogeneous mixtures of glycoforms, with structural variability in both domains. Traditionally, the oligosaccharide and lipid A components of LOS have been analyzed separately following mild acid hydrolysis, although important acid-labile moieties can be cleaved. Recently, an improved method was introduced for analysis of intact LOS by MALDI-TOF MS using a thin layer matrix composed of 2,4,6-trihydroxyacetophenone (THAP) and nitrocellulose. In addition to molecular ions, the spectra show in-source "prompt" fragments arising from regiospecific cleavage between the lipid A and oligosaccharide domains. Here, we demonstrate the use of traveling wave ion mobility spectrometry (TWIMS) for IMS-MS and IMS-MS/MS analyses of intact LOS from Neisseria spp. ionized by MALDI. Using IMS, the singly charged prompt fragments for the oligosaccharide and lipid A domains of LOS were readily separated into resolved ion plumes, permitting the extraction of specific subspectra, which led to increased confidence in assigning compositions and improved detection of less abundant ions. Moreover, IMS separation of precursor ions prior to collision-induced dissociation (CID) generated time-aligned, clean MS/MS spectra devoid of fragments from interfering species. Incorporating IMS into the profiling of intact LOS by MALDI-TOF MS exploits the unique domain structure of the molecule and offers a new means of extracting more detailed information from the analysis. Graphical Abstract ᅟ.

Lipooligosaccharide Structures of Invasive and Carrier Isolates of Neisseria meningitidis Are Correlated with Pathogenicity and Carriage

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.

Lack of lipid A pyrophosphorylation and functional lptA reduces inflammation by Neisseria commensals

The interaction of the immune system with Neisseria commensals remains poorly understood. We have previously shown that phosphoethanolamine on the lipid A portion of lipooligosaccharide (LOS) plays an important role in Toll-like receptor 4 (TLR4) signaling. For pathogenic Neisseria, phosphoethanolamine is added to lipid A by the phosphoethanolamine transferase specific for lipid A, which is encoded by lptA. Here, we report that Southern hybridizations and bioinformatics analyses of genomic sequences from all eight commensal Neisseria species confirmed that lptA was absent in 15 of 17 strains examined but was present in N. lactamica. Mass spectrometry of lipid A and intact LOS revealed the lack of both pyrophosphorylation and phosphoethanolaminylation in lipid A of commensal species lacking lptA. Inflammatory signaling in human THP-1 monocytic cells was much greater with pathogenic than with commensal Neisseria strains that lacked lptA, and greater sensitivity to polymyxin B was consistent with the absence of phosphoethanolamine. Unlike the other commensals, whole bacteria of two N. lactamica commensal strains had low inflammatory potential, whereas their lipid A had high-level pyrophosphorylation and phosphoethanolaminylation and induced high-level inflammatory signaling, supporting previous studies indicating that this species uses mechanisms other than altering lipid A to support commensalism. A meningococcal lptA deletion mutant had reduced inflammatory potential, further illustrating the importance of lipid A pyrophosphorylation and phosphoethanolaminylation in the bioactivity of LOS. Overall, our results indicate that lack of pyrophosphorylation and phosphoethanolaminylation of lipid A contributes to the immune privilege of most commensal Neisseria strains by reducing the inflammatory potential of LOS.

Urethral exudates of men with Neisseria gonorrhoeae infections select a restricted lipooligosaccharide phenotype during transmission

Neisseria gonorrhoeae lipooligosaccharides (LOSs) induce immunoglobulin G that protects men from experimental infection. This raises the possibility that an LOS vaccine might prevent gonorrhea. Gonococci make different LOS molecules, depending on whether 3 genes, lgtA, lgtC, and lgtD, are in frame (IF) or out of frame (OOF). Mispairing of polymeric guanine (polyG) tracts within each gene determines its frame during replication. We amplified lgtA, lgtC, and lgtD from diagnostic slides of urethral exudates and sequenced their polyG tracts. We found that lgtA in exudative bacteria is IF and that lgtC is OOF. The frame of lgtD varied widely: it was OOF in most but not all cases. This genotype would result in synthesis of polylactosamine α chains that could be sialylated. Polylactosamine α chains would enhance virulence, and their sialylation would enable gonococci to survive within polymorphonuclear cells; however, an active LgtD in a few bacteria could provide a survival advantage in other sites of infection.