Neutrophil extracellular traps (NETs) are implicated in autoimmunity but how they are generated and their roles in sterile inflammation remain unclear. Ribonucleoprotein immune complexes, inducers of NETosis, require mitochondrial ROS for maximal NET stimulation. During this process, mitochondria become hypopolarized and translocate to the cell surface. Extracellular release of oxidized mitochondrial DNA is proinflammatory in vitro and, when injected into mice, stimulates type-I interferon (IFN) signaling through a pathway dependent on the DNA sensor, STING. Mitochondrial ROS is also necessary for spontaneous NETosis of low-density granulocytes from individuals with systemic lupus erythematosus (SLE). This was also observed in individuals with chronic granulomatous disease (CGD), which lack NADPH-oxidase activity, but still develop autoimmunity and type I-IFN signatures. Mitochondrial ROS inhibition in vivo reduces disease severity and type-I IFN responses in a mouse model of lupus. These findings highlight a role for mitochondria in the generation not only of NETs but also of pro-inflammatory oxidized mitochondrial DNA in autoimmune diseases.

Ongoing inflammation including activation of the complement system is a hallmark of systemic lupus erythematosus (SLE). Antimicrobial neutrophil extracellular traps (NETs) are composed of secreted chromatin that may act as a source of autoantigens typical for SLE. In this study, we investigated how complement interacts with NETs and how NET degradation is affected by complement in SLE patients. We found that sera from a subset of patients with active SLE had a reduced ability to degrade in vitro-generated NETs, which was mostly restored when these patients were in remission. Patients that failed to degrade NETs had a more active disease and they also displayed lower levels of complement proteins C4 and C3 in blood. We discovered that NETs activated complement in vitro and that deposited C1q inhibited NET degradation including a direct inhibition of DNase-I by C1q. Complement deposition on NETs may facilitate autoantibody production, and indeed, Abs against NETs and NET epitopes were more pronounced in patients with impaired ability to degrade NETs. NET-bound autoantibodies inhibited degradation but also further increased C1q deposition, potentially exacerbating the disease. Thus, NETs are a potent complement activator, and this interaction may play an important role in SLE. Targeting complement with inhibitors or by removing complement activators such as NETs could be beneficial for patients with SLE.

Objective. To evaluate the specificity of expression patterns of cell-free circulating microRNAs (miRNAs) in systemic lupus erythematosus (SLE).Methods. Total RNA was purified from plasma, and 45 different specific, mature miRNAs were determined using quantitative reverse transcriptionpolymerase chain reaction assays. A total of 409 plasma samples were obtained from 364 different patients with SLE, healthy control subjects, and control subjects with other autoimmune diseases. The results in the primary cohort of 62 patients with SLE and 29 healthy control subjects were validated in 2 independent cohorts: a validation cohort comprising 68 patients with SLE and 68 healthy control subjects, and a disease control cohort comprising 20 patients with SLE (19 of whom were from the other validation cohort), 46 healthy control subjects, 38 patients with vasculitis, 18 patients with rheumatoid arthritis, and 20 immunosuppressed patients.Results. Seven miRNAs were statistically significantly differentially expressed in plasma from patients with SLE. The expression of miRNA-142-3p (miR-142-3p) and miR-181a was increased, and the expression of miR-106a, miR-17, miR-20a, miR-203, and miR-92a was decreased. In addition, the expression of miR-342-3p, miR-223, and miR-20a was significantly decreased in SLE patients with active nephritis. A predictive model for SLE based on 2 or 4 miRNAs differentiated patients with SLE from control subjects (76% accuracy) when validated independently (P < 2 ؋ 10 ؊9 ). Use of the 4-miRNA model provided highly significant differentiation between the SLE group and disease controls, except for those with vasculitis.Conclusion. Circulating miRNAs are systematically altered in SLE. A 4-miRNA signature was diagnostic of SLE, and a specific subset of miRNA profiles was associated with nephritis. All of the signature miRNAs target genes in the transforming growth factor ␤ signaling pathways. Other targets include regulation of apoptosis, cytokine-cytokine receptors, T cell development, and cytoskeletal organization. These findings highlight possible dysregulated pathways in SLE and suggest that circulating miRNA patterns distinguish SLE from other immunoinflammatory phenotypes.The autoimmune disease systemic lupus erythematosus (SLE) is characterized by multiple immunologic abnormalities including the presence of circulating antinuclear antibodies and a sustained type I interferon (IFN) response (1), with up-regulation of type I IFN-