title: The Carbohydrate-linked Phosphorylcholine of the Parasitic Nematode Product ES-62 Modulates Complement Activation.
abstract: Parasitic nematodes manufacture various carbohydrate-linked phosphorylcholine (PCh)-containing molecules, including ES-62, a protein with an N-linked glycan terminally substituted with PCh. The PCh component is biologically important because it is required for immunomodulatory effects. We showed that most ES-62 was bound to a single protein, C-reactive protein (CRP), in normal human serum, displaying a calcium-dependent, high-avidity interaction and ability to form large complexes. Unexpectedly, CRP binding to ES-62 failed to efficiently activate complement as far as the C3 convertase stage in comparison with PCh-BSA and PCh-containing Streptococcus pneumoniae cell wall polysaccharide. C1q capture assays demonstrated an ES-62-CRP-C1q interaction in serum. The three ligands all activated C1 and generated C4b to similar extents. However, a C2a active site was not generated following ES-62 binding to CRP, demonstrating that C2 cleavage was far less efficient for ES-62-containing complexes. We proposed that failure of C2 cleavage was due to the flexible nature of carbohydrate-bound PCh and that reduced proximity of the C1 complex was the reason that C2 was poorly cleaved. This was confirmed using synthetic analogues that were similar to ES-62 only in respect of having a flexible PCh. Furthermore, ES-62 was shown to deplete early complement components, such as the rate-limiting C4, following CRP interaction and thereby inhibit classical pathway activation. Thus, flexible PCh-glycan represents a novel mechanism for subversion of complement activation. These data illustrate the importance of the rate-limiting C4/C2 stage of complement activation and reveal a new addition to the repertoire of ES-62 immunomodulatory mechanisms with possible therapeutic applications.
authors.affiliation: From the Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT and.
authors.forename: Umul Kulthum
authors.initials: UK
authors.lastname: Ahmed
authors.affiliation: From the Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT and.
authors.forename: N Claire
authors.initials: NC
authors.lastname: Maller
authors.affiliation: From the Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT and.
authors.forename: Asif J
authors.initials: AJ
authors.lastname: Iqbal
authors.affiliation: the Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow G4 0RE, United Kingdom.
authors.forename: Lamyaa
authors.initials: L
authors.lastname: Al-Riyami
authors.affiliation: the Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow G4 0RE, United Kingdom.
authors.forename: William
authors.initials: W
authors.lastname: Harnett
authors.affiliation: From the Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT and john.raynes@lshtm.ac.uk.
authors.forename: John G
authors.initials: JG
authors.lastname: Raynes
mesh_terms: D001665:Binding Sites; D002097:C-Reactive Protein / Q000378:metabolism; D002236:Carbohydrate Conformation; D003167:Complement Activation / Q000187:drug effects*; D003175:Complement C2 / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism*; D003171:Complement Pathway, Classical / Q000187:drug effects*; D015801:Helminth Proteins / Q000494:pharmacology*; D006801:Humans; D010767:Phosphorylcholine / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D003175:Complement C2; D003181:Complement C4; C435884:ES-62 protein, Acanthocheilonema viteae; D015801:Helminth Proteins; D010767:Phosphorylcholine; D002097:C-Reactive Protein; D050577:Complement C3-C5 Convertases
keywords: C-reactive protein; C1Q complex (C1QA); ES-62; acute phase reactant; carbohydrate function; complement; immunomodulation; parasite; pentraxin; phosphorylcholine