naRNA is a canonical neutrophil extracellular trap (NET) component and novel inflammation-amplifying composite DAMP

Neutrophil extracellular traps (NETs) are a key antimicrobial feature of cellular innate immunity mediated by polymorphonuclear neutrophils (PMNs), the primary human leukocyte population. NETs trap and kill microbes but have also been linked to inflammation, e.g. atherosclerosis, arthritis or psoriasis by unknown mechanisms. We here characterize naRNA (NET-associated RNA), as a new canonical, abundant, and unexplored inflammatory NET component. naRNA, upon release by NET formation, drove further NET formation in naive PMN, and induced macrophage and keratinocyte activation via TLR8 in humans and Tlr13 in mice, in vitro and in vivo. Importantly, in vivo naRNA strongly drove skin inflammation, whereas genetic ablation of RNA sensing drastically ameliorated psoriatic skin inflammation. Rather than accidentally assembling with LL37 on the NET, naRNA was intracellularly pre-associated in resting neutrophils as a composite DAMP, thus highlighting NET formation as a DAMP release process. This re-defines sterile NETs as an intentionally inflammatory agent, signaling and amplifying neutrophil activation. Moreover, in the many conditions previously linked to NETs and extracellular RNA, TLR-mediated naRNA sensing emerges as both potential cause and new intervention target. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=175 SRC="FIGDIR/small/499571v4_ufig1.gif" ALT="Figure 1"> View larger version (94K): org.highwire.dtl.DTLVardef@11b866org.highwire.dtl.DTLVardef@16139ceorg.highwire.dtl.DTLVardef@1a2905org.highwire.dtl.DTLVardef@17b0e7e_HPS_FORMAT_FIGEXP M_FIG C_FIG Created with biorender.com