Carrier-dependent suppression of the anti-phosphorylcholine plaque-forming cell response in Trichinella-infected mice is mediated by anti-hapten IgG1 antibodies

Phosphocholine-Modified Macromolecules and Canonical Nicotinic Agonists Inhibit ATP-Induced IL-1β Release

IL-1β is a potent proinflammatory cytokine of the innate immune system that is involved in host defense against infection. However, increased production of IL-1β plays a pathogenic role in various inflammatory diseases, such as rheumatoid arthritis, gout, sepsis, stroke, and transplant rejection. To prevent detrimental collateral damage, IL-1β release is tightly controlled and typically requires two consecutive danger signals. LPS from Gram-negative bacteria is a prototypical first signal inducing pro-IL-1β synthesis, whereas extracellular ATP is a typical second signal sensed by the ATP receptor P2X7 that triggers activation of the NLRP3-containing inflammasome, proteolytic cleavage of pro-IL-1β by caspase-1, and release of mature IL-1β. Mechanisms controlling IL-1β release, even in the presence of both danger signals, are needed to protect from collateral damage and are of therapeutic interest. In this article, we show that acetylcholine, choline, phosphocholine, phosphocholine-modified LPS from Haemophilus influenzae, and phosphocholine-modified protein efficiently inhibit ATP-mediated IL-1β release in human and rat monocytes via nicotinic acetylcholine receptors containing subunits α7, α9, and/or α10. Of note, we identify receptors for phosphocholine-modified macromolecules that are synthesized by microbes and eukaryotic parasites and are well-known modulators of the immune system. Our data suggest that an endogenous anti-inflammatory cholinergic control mechanism effectively controls ATP-mediated release of IL-1β and that the same mechanism is used by symbionts and misused by parasites to evade innate immune responses of the host.

Detection and site localization of phosphorylcholine-modified peptides by NanoLC-ESI-MS/MS using precursor ion scanning and multiple reaction monitoring experiments

Phosphorylcholine (PC)-modified biomolecules like lipopolysaccharides, glycosphingolipids, and (glyco)proteins are widespread, highly relevant antigens of parasites, since this small hapten shows potent immunomodulatory capacity, which allows the establishment of long-lasting infections of the host. Especially for PC-modified proteins, structural data is rare because of the zwitterionic nature of the PC substituent, resulting in low sensitivities and unusual but characteristic fragmentation patterns. We have developed a targeted mass spectrometric approach using hybrid triple quadrupole/linear ion trap (QTRAP) mass spectrometry coupled to nanoflow chromatography for the sensitive detection of PC-modified peptides from complex proteolytic digests, and the localization of the PC-modification within the peptide backbone. In a first step, proteolytic digests are screened using precursor ion scanning for the marker ions of choline (m/z 104.1) and phosphorylcholine (m/z 184.1) to establish the presence of PC-modified peptides. Potential PC-modified precursors are then subjected to a second analysis using multiple reaction monitoring (MRM)-triggered product ion spectra for the identification and site localization of the modified peptides. The approach was first established using synthetic PC-modified synthetic peptides and PC-modified model digests. Following the optimization of key parameters, we then successfully applied the method to the detection of PC-peptides in the background of a proteolytic digest of a whole proteome. This methodological invention will greatly facilitate the detection of PC-substituted biomolecules and their structural analysis.

Identification of phosphorylcholine substituted peptides by their characteristic mass spectrometric fragmentation

Phosphorylcholine (PC) substituted biomolecules are wide-spread, highly relevant antigens of parasites, since this small hapten has been found to be a potent immunomodulatory component which allows the establishment of long lasting infections of the host. Structural data, especially of protein bound PC-substituents, are still rare due to the observation that mass spectrometric analyses are mostly hampered by this zwitterionic substituent resulting in low sensitivities and unusual but characteristic fragmentation patterns. Here we investigated the fragmentation behaviour of synthetic PC-substituted peptides by matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization ion trap mass spectrometry. We could show that the predominant neutral loss of a trimethylamine unit (Hoffmann elimination) leads to cyclic phosphate derivatives which prevent further fragmentation of the peptide backbone by stabilizing the positive charge at this particular side chain. Knowledge of this PC-specific fragmentation might help to identify PC-substituted biomolecules and facilitate their structural analysis.

Mangifera indicaL. extract (Vimang) and mangiferin modulate mouse humoral immune responses

The present study investigated the effects of orally administered Vimang (an aqueous extract of Mangifera indica) and mangiferin (the major polyphenol present in Vimang) on mouse antibody responses induced by inoculation with spores of microsporidian parasites. Inoculation induced specific antibody production with an exponential timecourse, peaking after about one month. Vimang significantly inhibited this antibody production from about three weeks post-inoculation, and most markedly by four weeks post-inoculation; by contrast, mangiferin had no significant effect. Determination of Ig isotypes showed that the IgM to IgG switch began about four weeks post-inoculation, with IgG2a predominating. Vimang significantly inhibited IgG production, but had no effect on IgM. Mangiferin did no affect either IgM or IgG2a, but significantly enhanced production of IgG1 and IgG2b. Neither Vimang nor mangiferin enhanced specific antibody secretion by splenic plasma cells from mice inoculated with microsporidian spores, whether administered in vivo before serum extraction or in vitro to the culture medium. Inoculation with spores induced splenomegaly, which was significantly reduced by Vimang and significantly enhanced by mangiferin. These results suggest that components of Mangifera indica extracts may be of potential value for modulating the humoral response in different immunopathological disorders.

Characterization of two monoclonal antibodies raised in Btk(xid) mice that recognize phosphorylcholine-bearing antigens from Trichinella and other helminths

This study investigated the binding properties of two monoclonal antibodies (mAbs US1 and US2) raised in (CBA/n x BALB/c)F1 (NBF1) Btk(xid) male mice. Both mAbs show unusual specificity for phosphorylcholine (PC)-containing TSL4 antigens of Trichinella. Specifically, and in contrast to mAbs raised in normal mice, US1 and US2 mAbs do not bind to artificial PC-protein conjugates and are not inhibited by either free PC or NPPC, although US2 was partially inhibited by NPPC at high concentration (10(-2) M). However, both mAbs completely abrogate the binding to Trichinella antigens of other anti-PC mAbs (e.g. BH8 and Mab-2). These results suggest that both US1 and US2 recognize complex PC-containing epitopes. The patterns of recognition of PC-bearing antigens from different helminths by US1, US2, Mab-2 and BH8 were broadly correlated with phylogenetic proximity. The closest similarities were observed between the members of the Trichinelloidea superfamily (Trichinella spiralis and Trichuris muris) and among the ascarids (Toxocara canis, Anisakis simplex, Hysterothylacium aduncum and Ascaris lumbricoides). However, US1 did not react with the filarial nematode Onchocerca volvulus and reacted only weakly with Onchocerca gibsoni, while US2 reacted only weakly with both species. Only BH8 recognized PC-bearing antigens from the trematode Fasciola hepatica and the cestode Bothriocephalus scorpii. These results suggest that PC is attached to identical or very similar structures on most different nematode species, although major differences exist with respect to helminth species from groups such as the trematodes and cestodes that are phylogenetically distant from the nematodes.

Phosphorylcholine substituents in nematodes: structures, occurrence and biological implications

Phosphorylcholine (PC), a small haptenic molecule, is found in a wide variety of prokaryotic organisms, i. e. bacteria, and in eukaryotic parasites such as nematodes, as well as in fungi. Linked to parasite-specific glycoprotein glycans or glycolipids, it is assumed to be responsible for a variety of immunological effects, including invasion mechanisms and long-term persistence of parasites within the host. Numerous reports have indicated various effects of PC-substituted molecules derived from parasitic nematodes on signal transduction pathways in B and T lymphocytes, displaying a highly adapted and profound modulation of the immune system by these parasites. The Nematoda, comprising parasitic and free-living species, can be regarded as promising prototypic systems for structural analyses, immunological studies and biosynthetic investigations. In this context, Ascaris suum, the pig parasitic nematode, is an ideal organism for immunological studies and an excellent source for obtaining large amounts of PC-substituted (macro)molecules. Caenorhabditis elegans, as a completely genome-sequenced species and expressing parasite analogous PC-substituted structures, together with the possibility for easy in vitro cultivation, represents a conceptual model for biosynthetic studies, whereas filarial parasites represent important model systems for human pathogens, especially in developing countries. This review summarises current knowledge on the tissue-specific expression of PC epitopes, structural data of glycoprotein glycans and glycosphingolipids bearing this substituent and biological implications for the immune systems of the respective hosts.