NET-derived DNA is associated with cGAS-STING and type I IFN responses, as supported by monocyte stimulation cultures using plasma from female patients with SLE

BACKGROUND: Neutrophil extracellular traps (NETs) are implicated in type I interferon (IFN) production in Systemic Lupus Erythematosus (SLE). While NETs are known to activate plasmacytoid dendritic cells (pDCs) via binding to Toll-like receptors, their effects on other immune cells remain underexplored. This study investigated whether NETs in plasma from patients with active SLE trigger cGAS-STING signalling in monocytes and induce the production of type I IFN and other immunomodulatory cytokines. METHODS: Monocytes from healthy donors were cultured with diluted plasma from healthy donors or patients with SLE across varying disease activity, or with in vitro-generated NETs. Activation of the cGAS-STING pathway was assessed by flow cytometric analysis of phosphorylated STING (pSTING) and TBK1 (pTBK1). Cytokine production, including type I IFNs, was quantified using bead-based immunoassays. Only female donor samples meeting the study eligibility criteria were available for inclusion in this cohort. FINDINGS: Plasma MPO-DNA levels correlated with IFNβ levels in patients with SLE (P = 0.002). SLE plasma induced STING and TBK1 phosphorylation, and IFNβ expression in healthy monocytes, with responses increasing according to donor disease activity (P < 0.0005). Experiments with healthy monocytes exposed to in vitro-generated NETs recapitulated these findings, evidenced by increased pSTING and pTBK1 expression and enhanced IFNα and IFNβ secretion (P < 0.05), which were inhibited by cGAS-IN-1. INTERPRETATION: Our findings support a role for NET-associated DNA in activating cGAS-STING signalling and promoting type I IFN production by monocytes in SLE. These findings identify NET-mediated cGAS-STING signalling in monocytes as a pathway that warrants further investigation in the context of type I IFN-driven inflammation in SLE. FUNDING: Not Applicable.