Type I IFN drives unconventional IL-1β secretion in lupus monocytes.

Opsonization of red blood cells that retain mitochondria (Mito+ RBCs), a feature of systemic lupus erythematosus (SLE), triggers type I interferon (IFN) production in macrophages. We report that monocytes (Mos) co-produce IFN and mature interleukin-1β (mIL-1β) upon Mito+ RBC opsonization. IFN expression depended on cyclic GMP-AMP synthase (cGAS) and RIG-I-like receptors' (RLRs) sensing of Mito+ RBC-derived mitochondrial DNA (mtDNA) and mtRNA, respectively. Interleukin-1β (IL-1β) production was initiated by the RLR antiviral signaling adaptor (MAVS) pathway recognition of Mito+ RBC-derived mtRNA. This led to the cytosolic release of Mo mtDNA, which activated the inflammasome. Importantly, mIL-1β secretion was independent of gasdermin D (GSDMD) and pyroptosis but relied on IFN-inducible myxovirus-resistant protein 1 (MxA), which facilitated the incorporation of mIL-1β into a trans -Golgi network (TGN)-mediated secretory pathway. RBC internalization identified a subset of blood Mo expressing IFN-stimulated genes (ISGs) that released mIL-1β and expanded in SLE patients with active disease. [Display omitted] • Mos co-produce type I IFN and IL-1β upon Mito+ RBC opsonization • IFN and IL-1β expression rely on sensing RBC-derived mtDNA and mtRNA • IL-1β secretion is MxA mediated and independent of GSDMD and pyroptosis • GPA+ blood Mos expressing IFN and IL-1β are expanded in active SLE SLE is an interferonopathy, but blocking IFN does not benefit all patients. Caielli et al. found that SLE monocytes co-produce IFN and IL-1β, a phenotype recapitulated upon in vitro Mito+ RBC opsonization. Cytosolic sensing of mitochondrial nucleic acids induces MxA, which enables IL-1β secretion independently of GSDMD and pyroptosis. [ABSTRACT FROM AUTHOR]