O003 Characterising the role of net-derived IL-33 in SLE pathogenesis
Authors: S Georgakis, G Papadaki, I Gergianaki, C Adamichou, S Polia, P Sidiropoulos, P Verginis, K Gkirtzimanaki, G Bertsias
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Introduction</h3> Interleukin (IL)−33 is a cell necrosis-derived alarmin with immunostimulatory properties which depends on the context of immune cells and the inflammatory milieu.<sup>1,2</sup> In Systemic Lupus Erythematosus (SLE), extracellular DNA (as in extracellular chromatin traps [NETs] or immune complexes [ICs]) combined with alarmins stimulate innate immunity receptors (such as Toll-like receptors [TLRs]) and the production of IFNa by plasmatocytoid dendritic cells (pDCs).<sup>3,4</sup> <h3>Objectives</h3> We hypothesised that bioactive NET-derived isoforms of IL-33 might augment the interferogenic potential of extracellular DNA in SLE. <h3>Methods</h3> Peripheral blood polymorphonuclear cells (PMNs) were isolated from healthy and SLE individuals and their ability to form IL33-decorated NETs was assessed by confocal microscopy. NET-supernatants from untreated and IC-treated SLE PMNs were administrated to healthy pDCs and type I IFN production was monitored by qPCR and ELISA. The contribution of IL-33 in the interferogenic capacity of NETs was addressed by pre-treating pDCs with a specific mAb against IL33-receptor (anti-ST2L). Western blotting of SLE and healthy PMNs was used to detect different isoforms of IL-33. <h3>Results</h3> Spontaneous-released NETs from peripheral blood PMNs of active SLE patients were decorated with IL-33 to a larger extent as compared to healthy PMN NETs. Treatment of SLE PMNs with ICs led to the release of NETs with extended IL-33 decoration and enhanced interferogenic capacity. IL33 receptor blockade significantly decreased the type I IFN response of NET-treated control pDCs. DNase treatment of NETs to disrupt their structure resulted in reduced interferogenic capacity and abrogated the pro-inflammatory effect of IL-33. Finally, western blotting on IC-mediated SLE NETs revealed the presence of cleaved isoforms of IL-33 which closely resemble the previously characterised highly bioactive isoforms of our protein of interest. Experiments are underway to explore the possible role of NET-bound proteases in IL-33 activation. <h3>Conclusions</h3> NET-derived IL-33 is a novel mediator of the nucleic acid-driven aberrant type I IFN response which exacerbates SLE disease. NET structure may be crucial in regulating the bioactivity of IL-33. <h3>References</h3> . Foo Yew Liew, et al. Intereleukin-33 in health and disease. <i>Nature Reviews</i>2016. . Lefrancais E. IL-33 is processed in mature bioactive isoforms by neutrophil elastase and cathepsin G. PNAs2012 . Garcia Romo G. Netting neutrophils are major inducers of type I IFN production in paediatric systemic lupus erythematosus. Science Translational Medicine2011. . Lande R. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature2007. <h3>Acknowledgements</h3> We thank Dr. Ronnblom and Dr Eloranta for providing us with immune complexes material for our scientific project. <h3>Disclosure of interest</h3> None declared