human iggfcγr interactions are modulated by streptococcal igg glycan hydrolysis人类iggfcγr交互由链球菌免疫球蛋白g多糖水解调制.pdfVIP

Human IgG/FccR Interactions Are Modulated by Streptococcal IgG Glycan Hydrolysis 1 1 2 1 Maria Allhorn *, Anders I. Olin , Falk Nimmerjahn , Mattias Collin 1 Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden, 2 Experimental Immunology and Immunotherapy, Nikolaus-Fiebiger-Center for Molecular Medicine, Erlangen, Germany Background. The human pathogen Streptococcus pyogenes produces an endoglycosidase, EndoS that hydrolyzes the chitobiose core of the asparagine-linked glycan on the heavy chain of human IgG. IgG-binding to Fc gamma receptors (FccR) on leukocytes triggers effector functions including phagocytosis, oxidative burst and the release of inflammatory mediators. The interactions between FccR and the Fc domain of IgG depend on the IgG glycosylation state. Methodology/Principal Findings. Here we show for the first time that EndoS hydrolyzes the heavy chain glycan of all four human IgG subclasses (IgG1-4), in purified form and in a plasma environment. An inactive form of EndoS, obtained by site-directed mutagenesis, binds IgG with high affinity, in contrast to wild type EndoS that only transiently interacts with IgG, as shown by Slot-blotting and surface plasmon resonance technology. Furthermore, EndoS hydrolysis of the IgG glycan influences the binding of IgG to immobilized soluble FccR and to an erythroleukemic cell line, K562, expressing FccRIIa. Incubation of whole blood with EndoS results in a dramatic decrease of IgG binding to activated monocytes as analyzed by flow cytometry. Moreover, the IgG bound to K562 cells dissociates when cells are treated with EndoS. Likewise, IgG bound to immobilized FccRIIa and subsequently treated with EndoS, dissociates from the receptor as analyzed by surface plasmon resonance a