P032 Sialic acids inhibit neutrophil extracellular trap formation

Career situation of first and presenting author Student for a master or a PhD Introduction In rheumatoid arthritis (RA) activated neutrophils produce neutrophil extracellular traps (NETs), which provide a source of autoantigens that drives the autoimmune process.1 To identify novel immune processes that dampened neutrophil activity, we investigated a family of inhibitory glycan-binding receptors (Siglecs) that bind a specific type of glycan; called sialic acids.2 We hypothesize that sialic acid-mediated triggering of siglecs on neutrophils, which express siglec-5, –9 and −14, will reduce their activation. In this study we focused on dampening the activity of neutrophils and thereby NET formation. Methods Polymorphonuclear cells (PMNs) were isolated from healthy donors. Neutrophil binding of sialic acid-containing glycoconjugates was assessed by flow cytometry. Neutralizing antibodies for siglec-5/14 and −9 were used to block the interaction with the sialic acid glycoconjugates. For functional assays a branched synthetic molecule containing sialic acids (sialic acid dendrimer) was used. PMNs were rested for 1 hour at 37°C followed by stimulation of sialic acids dendrimers for 30 min. Subsequently, IgA coated beads were added for 30 min to activate the neutrophils. NETosis was quantified via Sytoxgreen and visualised via microscopy, and phagocytosis was measured by flow cytometry. Results Binding of sialic acid glycoconjugates was observed on neutrophils. Neutralizing siglec-5/14 and −9 receptor almost completely abolished sialic acid glycoconjugate binding to neutrophils. Neutrophils activated with IgA beads released NETs, as confirmed via microscopy. Triggering neutrophils with sialic acid dendrimer reduced this process of NETosis. The capacity to engulf IgA beads was not affected by sialic acid dendrimer stimulation. Conclusions Neutrophils stimulated with sialic acid dendrimers show reduced activation. Patients with RA might benefit from treatment with sialic acid to dampen neutrophil-mediated autoimmune response. References Wright HL, Moots RJ, Edwards SW. The multifactorial role of neutrophils in rheumatoid arthritis. Nat Rev Rheumatol 2014;10(10):593–601. Macauley MS, Crocker PR, Paulson JC. Siglec-mediated regulation of immune cell function in disease. Nat Rev Immunol 2014;14(10):653–66. Disclosure of Interest None declared.