Macrophage-1 antigen exacerbates histone-induced acute lung injury and promotes neutrophil extracellular trap formation

Acute lung injury (ALI), which occurs in association with sepsis, trauma, and coronavirus disease 2019 (COVID-19), is a serious clinical condition with high mortality. Excessive platelet-leukocyte aggregate (PLA) formation promotes neutrophil extracellular trap (NET) release and thrombosis, which are involved in various diseases, including ALI. Macrophage-1 antigen (Mac-1, CD11b/CD18), which is expressed on the surface of leukocytes, is known to promote NET formation. This study aimed to elucidate the role of Mac-1 in extracellular histone-induced ALI. Exogenous histones were administered to Mac-1-deficient mice and wild-type (WT) mice with or without neutrophil or platelet depletion, and several parameters were investigated 1 h after histone injection. Depletion of neutrophils or platelets improved survival time and macroscopic and microscopic properties of lung tissues, and decreased platelet-leukocyte formation and plasma myeloperoxidase levels. These improvements were also observed in Mac-1-/- mice. NET formation in Mac-1-/- bone marrow neutrophils (BMNs) was significantly lower than that in WT BMNs. In conclusion, our findings suggest that Mac-1 is associated with exacerbation of histone-induced ALI and the promotion of NET formation in the presence of activated platelets.

The Oxysterol Receptor EBI2 Links Innate and Adaptive Immunity to Limit IFN Response and Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with abnormal activation of the immune system. Recent attention is increasing about how aberrant lipid and cholesterol metabolism is linked together with type I interferon (IFN-I) signaling in the regulation of the pathogenesis of SLE. Here, a metabonomic analysis is performed and increased plasma concentrations of oxysterols, especially 7α, 25-dihydroxycholesterol (7α, 25-OHC), are identified in SLE patients. The authors find that 7α, 25-OHC binding to its receptor Epstein-Barr virus-induced gene 2 (EBI2) in macrophages can suppress STAT activation and the production of IFN-β, chemokines, and cytokines. Importantly, monocytes/macrophages from SLE patients and mice show significantly reduced EBI2 expression, which can be triggered by IFN-γ produced in activated T cells. Previous findings suggest that EBI2 enhances immune cell migration. Opposite to this effect, the authors demonstrate that EBI2-deficient macrophages produce higher levels of chemokines and cytokines, which recruits and activates myeloid cells,T and B lymphocytes to exacerbate tetramethylpentadecane-induced SLE. Together, via sensing the oxysterol 7α, 25-OHC, EBI2 in macrophages can modulate innate and adaptive immune responses, which may be used as a potential diagnostic marker and therapeutic target for SLE.

A novel monocyte differentiation pattern in pristane-induced lupus with diffuse alveolar hemorrhage

Pristane causes chronic peritoneal inflammation resulting in lupus, which in C57BL/6 mice is complicated by lung microvascular injury and diffuse alveolar hemorrhage (DAH). Mineral oil (MO) also causes inflammation, but not lupus or DAH. Since monocyte depletion prevents DAH, we examined the role of monocytes in the disease. Impaired bone marrow (BM) monocyte egress in Ccr2-/- mice abolished DAH, confirming the importance of monocyte recruitment to the lung. Circulating Ly6Chi monocytes from pristane-treated mice exhibited increased annexin-V staining in comparison with MO-treated controls without evidence of apoptosis, suggesting that pristane alters the distribution of phosphatidylserine in the plasma membrane before or shortly after monocyte egress from the BM. Plasma membrane asymmetry also was impaired in Nr4a1-regulated Ly6Clo/- 'patrolling' monocytes, which are derived from Ly6Chi precursors. Patrolling Ly6Clo/- monocytes normally promote endothelial repair, but their phenotype was altered in pristane-treated mice. In contrast to MO-treated controls, Nr4a1-regulated Ly6Clo/- monocytes from pristane-treated mice were CD138+, expressed more TremL4, a protein that amplifies TLR7 signaling, and exuberantly produced TNFα in response to TLR7 stimulation. TremL4 expression on these novel CD138+ monocytes was regulated by Nr4a1. Thus, monocyte CD138, high TremL4 expression, and annexin-V staining may define an activated/inflammatory subtype of patrolling monocytes associated with DAH susceptibility. By altering monocyte development, pristane exposure may generate activated Ly6Chi and Ly6Clo/- monocytes, contributing to lung microvascular endothelial injury and DAH susceptibility.

TANK prevents IFN-dependent fatal diffuse alveolar hemorrhage by suppressing DNA-cGAS aggregation

Diffuse alveolar hemorrhage (DAH) is one of the serious complications associated with systemic lupus erythematosus, an autoimmune disease whose pathogenesis involves type I IFNs and cytokines. Here, we show that TANK, a negative regulator of the NF-κB signaling via suppression of TRAF6 ubiquitination, is critical for the amelioration of fatal DAH caused by lung vascular endothelial cell death in a mouse model of systemic lupus erythematosus. The development of fatal DAH in the absence of TANK is mediated by type I IFN signaling, but not IL-6. We further uncover that STING, an adaptor essential for the signaling of cytoplasmic DNA sensor cyclic GMP-AMP (cGAMP) synthase (cGAS), plays a critical role in DAH under Tank deficiency. TANK controls cGAS-mediated cGAMP production and suppresses DNA-mediated induction of IFN-stimulated genes in macrophages by inhibiting the formation of DNA-cGAS aggregates containing ubiquitin. Collectively, TANK inhibits the cGAS-dependent recognition of cytoplasmic DNA to prevent fatal DAH in the murine lupus model.

SMS2 deficiency impairs PKCδ-regulated B cell tolerance in the germinal center

B cell tolerance prevents autoimmunity by deleting or deactivating autoreactive B cells that otherwise may cause autoantibody-driven disorders, including systemic lupus erythematosus (lupus). Lupus is characterized by immunoglobulin Gs carrying a double-stranded (ds)-DNA autospecificity derived mainly from somatic hypermutation in the germinal center (GC), pointing to a checkpoint breach of GC B cell tolerance that leads to lupus. However, tolerance mechanisms in the GC remain poorly understood. Here, we show that upregulated sphingomyelin synthase 2 (SMS2) in anti-dsDNA GC B cells induces apoptosis by directly activating protein kinase C δ (PKCδ)'s pro-apoptotic activity. This tolerance mechanism prevents lupus autoimmunity in C57/BL6 mice and can be stimulated pharmacologically to inhibit lupus pathogenesis in lupus-prone NZBWF1 mice. Patients with lupus consistently have substantially reduced SMS2 expression in B cells and to an even greater extent in autoimmune-prone, age-associated B cells, suggesting that patients with lupus have insufficient SMS2-regulated B cell tolerance.

Myxomavirus serpin alters macrophage function and prevents diffuse alveolar hemorrhage in pristane-induced lupus

C57BL/6 mice with pristane-induced lupus develop macrophage-dependent diffuse alveolar hemorrhage (DAH), which is blocked by treatment with liver X receptor (LXR) agonists and is exacerbated by low IL-10 levels. Serp-1, a myxomavirus-encoded serpin that impairs macrophage activation and plasminogen activation, blocks DAH caused by MHV68 infection. We investigated whether Serp-1 also could block DAH in pristane-induced lupus. Pristane-induced DAH was prevented by treatment with recombinant Serp-1 and macrophages from Serp1-treated mice exhibited an anti-inflammatory M2-like phenotype. Therapy activated LXR, promoting M2 polarization and expression of Kruppel-like factor-4 (KLH4), which upregulates IL-10. In contrast, deficiency of tissue plasminogen activator or plasminogen activator inhibitor had little effect on DAH. We conclude that Serp-1 blocks pristane-induced lung hemorrhage by enhancing LXR-regulated M2 macrophage polarization and KLH4-regulated IL-10 production. In view of the similarities between DAH in pristane-treated mice and SLE patients, Serp-1 may represent a potential new therapy for this severe complication of SLE.

PEGylated Serp-1 Markedly Reduces Pristane-Induced Experimental Diffuse Alveolar Hemorrhage, Altering uPAR Distribution, and Macrophage Invasion

Diffuse alveolar hemorrhage (DAH) is one of the most serious clinical complications of systemic lupus erythematosus (SLE). The prevalence of DAH is reported to range from 1 to 5%, but while DAH is considered a rare complication there is a reported 50-80% mortality. There is at present no proven effective treatment for DAH and the therapeutics that have been tested have significant side effects. There is a clear necessity to discover new drugs to improve outcomes in DAH. Serine protease inhibitors, serpins, regulate thrombotic and thrombolytic protease cascades. We are investigating a Myxomavirus derived immune modulating serpin, Serp-1, as a new class of immune modulating therapeutics for vasculopathy and lung hemorrhage. Serp-1 has proven efficacy in models of herpes virus-induced arterial inflammation (vasculitis) and lung hemorrhage and has also proved safe in a clinical trial in patients with unstable coronary syndromes and stent implant. Here, we examine Serp-1, both as a native secreted protein expressed by CHO cells and as a polyethylene glycol modified (PEGylated) variant (Serp-1m5), for potential therapy in DAH. DAH was induced by intraperitoneal (IP) injection of pristane in C57BL/6J (B6) mice. Mice were treated with 100 ng/g bodyweight of either Serp-1 as native 55 kDa secreted glycoprotein, or as Serp-1m5, or saline controls after inducing DAH. Treatments were repeated daily for 14 days (6 mice/group). Serp-1 partially and Serp-1m5 significantly reduced pristane-induced DAH when compared with saline as assessed by gross pathology and H&E staining (Serp-1, p = 0.2172; Serp-1m5, p = 0.0252). Both Serp-1m5 and Serp-1 treatment reduced perivascular inflammation and reduced M1 macrophage (Serp-1, p = 0.0350; Serp-1m5, p = 0.0053), hemosiderin-laden macrophage (Serp-1, p = 0.0370; Serp-1m5, p = 0.0424) invasion, and complement C5b/9 staining. Extracellular urokinase-type plasminogen activator receptor positive (uPAR+) clusters were significantly reduced (Serp-1, p = 0.0172; Serp-1m5, p = 0.0025). Serp-1m5 also increased intact uPAR+ alveoli in the lung (p = 0.0091). In conclusion, Serp-1m5 significantly reduces lung damage and hemorrhage in a pristane model of SLE DAH, providing a new potential therapeutic approach.

Preclinical Testing of Viral Therapeutic Efficacy in Pristane-Induced Lupus Nephritis and Diffuse Alveolar Hemorrhage Mouse Models

Systemic lupus erythematosus (SLE) is a multifactorial and heterogeneous autoimmune disease involving multiple organ systems and tissues. Lupus nephritis occurs in approximately 60% of patients with SLE and is the leading cause of morbidity. Diffuse alveolar hemorrhage (DAH) is a rare but very serious complication of SLE with a greater than 50% associated mortality. The etiology of SLE is unclear but has proposed genetic, hormonal, and environmental aspects. Pristane is a saturated terpenoid alkane and has become the most popular laboratory model for inducing lupus in mice. The pristane model of SLE has the capacity to reproduce many components of the human presentation of the disease. Previous studies have demonstrated that virus-derived immune-modulating proteins have the potential to control inflammatory and autoimmune disorders. Serp-1, a 55 kDa secreted and highly glycosylated immune modulator derived from myxoma virus (MYXV), has potent immunomodulatory activity in models of vasculitis, viral sepsis, collagen-induced arthritis, and transplant rejection. This chapter describes the mouse preclinical pristane lupus model as a method to examine virus-derived protein efficacy for treating autoimmune diseases and specifically lupus nephritis and DAH.

Alpha-1-Antitrypsin Ameliorates Pristane Induced Diffuse Alveolar Hemorrhage in Mice

Diffuse alveolar hemorrhage (DAH) is a fatal complication in patients with lupus. DAH can be induced in B6 mice by an intraperitoneal injection of pristane. Since human alpha-1-antitrypsin (hAAT) is an anti-inflammatory and immuno-regulatory protein, we investigated the protective effect of hAAT against pristane-induced DAH in B6 mice and hAAT transgenic (hAAT-Tg) mice. We first showed that hAAT Tg expression lowers TNF-α production in B cells, as well as CD4+ T cells in untreated mice. Conversely, the frequency of regulatory CD4+CD25+ and CD4+CD25-IL-10+ cells was significantly higher in hAAT-Tg than in B6 mice. This confirmed the anti-inflammatory effect of hAAT that was observed even at steady state. One week after a pristane injection, the frequency of peritoneal Ly6C^hi inflammatory monocytes and neutrophils in hAAT-Tg mice was significantly lower than that in B6 mice. Importantly, pristane-induced DAH was completely prevented in hAAT-Tg mice and this was associated with a modulation of anti- to pro-inflammatory myeloid cell ratio/balance. We also showed that treatment with hAAT decreased the severity of DAH in B6 mice. These results showed for the first time that hAAT has a therapeutic potential for the treatment of DAH.

High-dimensional analysis reveals a pathogenic role of inflammatory monocytes in experimental diffuse alveolar hemorrhage

Diffuse alveolar hemorrhage (DAH) is a life-threatening pulmonary complication associated with systemic lupus erythematosus, vasculitis, and stem cell transplant. Little is known about the pathophysiology of DAH, and no targeted therapy is currently available. Pristane treatment in mice induces systemic autoimmunity and lung hemorrhage that recapitulates hallmark pathologic features of human DAH. Using this experimental model, we performed high-dimensional analysis of lung immune cells in DAH by mass cytometry and single-cell RNA sequencing. We found a large influx of myeloid cells to the lungs in DAH and defined the gene expression profile of infiltrating monocytes. Bone marrow-derived inflammatory monocytes actively migrated to the lungs and homed adjacent to blood vessels. Using 3 models of monocyte deficiency and complementary transfer studies, we established a central role of inflammatory monocytes in the development of DAH. We further found that the myeloid transcription factor interferon regulatory factor 8 is essential to the development of both DAH and type I interferon-dependent autoimmunity. These findings collectively reveal monocytes as a potential treatment target in DAH.

E3 ligase FBXW7 aggravates TMPD-induced systemic lupus erythematosus by promoting cell apoptosis

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease, and the pathogenesis of SLE has not been fully elucidated. The E3 ubiquitin ligase FBXW7 has been well characterized in cancer as a tumor suppressor that can promote the ubiquitination and subsequent degradation of various oncoproteins; however, the potential role of FBXW7 in autoimmune diseases is unclear. In the present study, we identified that FBXW7 is a crucial exacerbating factor for SLE development and progression in a mouse model induced by 2, 6, 10, 14-tetramethylpentadecane (TMPD). Myeloid cell-specific FBXW7-deficient (Lysm⁺FBXW7^f/f) C57BL/6 mice showed decreased immune complex accumulation, glomerulonephritis, glomerular mesangial cell proliferation, and base-membrane thickness in the kidney. Lysm⁺FBXW7^f/f mice produced fewer anti-Sm/RNP and anti-ANA autoantibodies and showed a decreased MHC II expression in B cells. In Lysm⁺FBXW7^f/f mice, we observed that cell apoptosis was reduced and that fewer CD11b⁺Ly6C^hi inflammatory monocytes were recruited to the peritoneal cavity. Consistently, diffuse pulmonary hemorrhage (DPH) was also decreased in Lysm⁺FBXW7^f/f mice. Mechanistically, we clarified that FBXW7 promoted TMPD-induced cell apoptosis by catalyzing MCL1 degradation through K48-linked ubiquitination. Our work revealed that FBXW7 expression in myeloid cells played a crucial role in TMPD-induced SLE progression in mice, which may provide novel ideas and theoretical support for understanding the pathogenesis of SLE.

Apoptosis inhibitor of macrophage ameliorates fungus-induced peritoneal injury model in mice

Fungal peritonitis in a patient on peritoneal dialysis (PD) is a refractory injury accompanied by severe inflammation, predisposing patients to a poor prognosis. Defective clearance of necrotic tissue interferes with amelioration of tissue injury and induces abnormal tissue remodeling. In the recent reports, apoptosis inhibitor of macrophage (AIM, also called CD5L) prevents obesity, hepatocellular carcinoma and acute kidney injury. Here, we investigated potential roles of AIM in prevention of progression of fungal peritonitis models. AIM^−/− mice subjected to zymosan-induced peritonitis exhibited progressive inflammation and sustained peritoneal necrosis tissue on day 28 after the disease induction, whereas there was an improvement in AIM^+/+ mice. This appeared to be caused by deposition of AIM at the necrotic peritoneum in AIM^+/+ mice. In vitro, AIM enhanced the engulfment of necrotic debris by macrophages derived from zymosan-induced peritonitis, M1- and M2a-like bone marrow derived macrophages, as well as by mesothelial cells. In addition, administration of recombinant AIM dramatically ameliorated severe inflammation associated with necrosis in zymosan-induced peritonitis of AIM^−/− mice. Our observations suggest that AIM appears to be involved in the repair process of zymosan-induced peritonitis, and thus, could be the basis of development of new therapeutic strategies for PD-related fungal peritonitis.

A Novel Mechanism for Generating the Interferon Signature in Lupus: Opsonization of Dead Cells by Complement and IgM

OBJECTIVE

In vitro studies suggest that the type I interferon (IFN) signature seen in most lupus patients results from Fcγ receptor-mediated uptake of nucleic acid-containing immune complexes by plasmacytoid dendritic cells and engagement of endosomal Toll-like receptors. The aim of this study was to reexamine the pathogenesis of the IFN signature in vivo.

METHODS

Lupus was induced in mice by injecting pristane. Some mice were treated with normal immunoglobulin or with cobra venom factor to deplete complement. The IFN signature was evaluated by polymerase chain reaction. The IFN signature also was determined in C4-deficient patients and control subjects.

RESULTS

Wild-type C57BL/6 mice with pristane-induced lupus developed a strong IFN signature, which was absent in immunoglobulin-deficient (μMT), C3^-/- , and CD18^-/- mice. Intravenous infusion of normal IgM, but not IgG, restored the IFN signature in μMT mice, and the IFN signature in wild-type mice was inhibited by depleting complement, suggesting that opsonization by IgM and complement is involved in IFN production. Consistent with that possibility, the levels of "natural" IgM antibodies reactive with dead cells were increased in pristane-treated wild-type mice compared with untreated controls, and in vivo phagocytosis of dead cells was impaired in C3-deficient mice. To examine the clinical relevance of these findings, we identified 10 C4-deficient patients with lupus-like disease and compared them with 152 C4-intact patients and 21 healthy controls. In comparison with C4-intact patients, C4-deficient patients had a different clinical/serologic phenotype and lacked the IFN signature.

CONCLUSION

These studies define previously unrecognized roles of natural IgM, complement, and complement receptors in generating the IFN signature in lupus.

Pathogenesis of Diffuse Alveolar Hemorrhage in Murine Lupus

OBJECTIVE

Diffuse alveolar hemorrhage (DAH) in lupus patients confers >50% mortality, and the cause is unknown. We undertook this study to examine the pathogenesis of DAH in C57BL/6 mice with pristane-induced lupus, a model of human lupus-associated DAH.

METHODS

Clinical/pathologic and immunologic manifestations of DAH in pristane-induced lupus were compared with those of DAH in humans. Tissue distribution of pristane was examined by mass spectrometry. Cell types responsible for disease were determined by in vivo depletion using clodronate liposomes and antineutrophil monoclonal antibodies (anti-Ly-6G). The effect of complement depletion with cobra venom factor (CVF) was examined.

RESULTS

After intraperitoneal injection, pristane migrated to the lung, causing cell death, small vessel vasculitis, and alveolar hemorrhage similar to that seen in DAH in humans. B cell-deficient mice were resistant to induction of DAH, but susceptibility was restored by infusing IgM. C3^-/- and CD18^-/- mice were also resistant, and DAH was prevented in wild-type mice by CVF. Induction of DAH was independent of Toll-like receptors, inflammasomes, and inducible nitric oxide. Mortality was increased in interleukin-10 (IL-10)-deficient mice, and pristane treatment decreased IL-10 receptor expression in monocytes and STAT-3 phosphorylation in lung macrophages. In vivo neutrophil depletion was not protective, while treatment with clodronate liposomes prevented DAH, which suggests that macrophage activation is central to DAH pathogenesis.

CONCLUSION

The pathogenesis of DAH involves opsonization of dead cells by natural IgM and complement followed by complement receptor-mediated lung inflammation. The disease is macrophage dependent, and IL-10 is protective. Complement inhibition and/or macrophage-targeted therapies may reduce mortality in lupus-associated DAH.

Transfusion of CD206+ M2 Macrophages Ameliorates Antibody-Mediated Glomerulonephritis in Mice

Macrophages are multifunctional immune cells that may either drive or modulate disease pathogenesis, depending on the activated phenotype. In this study, we investigated the protective effects of CD206⁺ M2 macrophages against nephrotoxic serum nephritis in mice. We found that these immunosuppressive macrophages, derived from bone marrow and stimulated with IL-4/IL-13 [CD206⁺ M2 bone marrow-derived macrophages (M2BMMs)], protected against renal injury, decreased proteinuria, and diminished the infiltration of CD68⁺ macrophages, neutrophils, and T cells into glomerular tissue. Comparable therapeutic results were obtained with CD206⁺ M2 cells derived from induced pluripotent stem cells. Notably, CD206⁺ M2BMMs, which retained an M2 signature, could elicit a switch of M1 to M2 phenotype in co-cultured macrophages. Moreover, these cells were found to induce the production of regulatory T cells in the spleen and renal draining lymph node. Accordingly, mRNA expression of the T helper 1 cytokines tumor necrosis factor-α, interferon-β, interferon-γ, and IL-12 was significantly reduced in kidneys from mice treated with CD206⁺ M2BMMs. Taken together, the data suggest that CD206⁺ M2 may have therapeutic potential against antibody-mediated glomerular injury and presents its therapeutic value for the treatment of crescentic nephritis in humans.

Milk fat globule-EGF factor 8 suppresses the aberrant immune response of systemic lupus erythematosus-derived neutrophils and associated tissue damage

Abnormal features of the systemic lupus erythematosus (SLE)-derived neutrophils, promoted aberrant immune response, have inspired new studies of the induction of autoimmunity and the development of organ damage in SLE. In this study, we explore the effect of milk fat globule-EGF factor 8 (MFG-E8) on the aberrant nitrification features in pristane-induced lupus. SLE patients and mice with pristane-induced lupus develop autoantibodies associated with MFG-E8 overproduction. However, the deletion of MFG-E8 leads to uncontrolled early pulmonary and peritoneal inflammation and tissue damage in mice with pristane-induced lupus. Consistent with these findings, MFG-E8-deficient mice that are exposed to pristane show enhanced neutrophil accumulation and increased neutrophil death, including apoptosis, necrosis and NETosis, as well as impaired phagocytosis of macrophages. The consequences are the expansion of diffuse pulmonary hemorrhage, increased anti-nuclear antibody, anti-dsDNA antibody and anti-neutrophil cytoplasmic antibody levels, and enhanced immune complexes deposition and neutrophil extracellular traps (NETs) formation in the lung and kidney tissues of MFG-E8-deficient mice exposed to pristane. In patients with SLE and mice with pristane-induced lupus, neutrophil accumulation is elevated, which depends on higher expression of the surface receptor CXCR2. After pretreatment with recombinant MFG-E8, the surface expression of CXCR2 on neutrophil is downregulated, and the MFG-E8 deletion increase CXCR2 expression by ~40%. These studies indicate that MFG-E8 reduces neutrophil migration and NETosis via downregulating surface CXCR2 expression in parallel with its role in the phagocytosis of apoptotic neutrophils, suggesting that MFG-E8 may serve as a therapeutic agent for attenuating the early inflammatory responses of SLE and protect patients from lupus-related damage.

In Vivo Therapeutic Success of MicroRNA-155 Antagomir in a Mouse Model of Lupus Alveolar Hemorrhage

OBJECTIVE

Diffuse alveolar hemorrhage (DAH) is a rare but life-threatening complication of systemic lupus erythematosus (SLE). Pristane-treated B6 mice develop severe DAH within 2 weeks of treatment. MicroRNA-155 (miR-155) is a pleiotropic microRNA that plays a crucial role in the regulation of immune responses. Recent studies have revealed a pathogenic role of miR-155 in various autoimmune disorders. The purpose of this study was to examine the role of miR-155 in the development of DAH in pristane-induced lupus using miR-155-knockout (miR-155(-/-)) mice and miR-155 antagomir to silence miR-155.

METHODS

DAH was induced by an intraperitoneal injection of 0.5 ml of pristane. MicroRNA-155 antagomir was administered intravenously to silence miR-155 expression. Lung tissues were collected for RNA extraction and were embedded in paraffin for sectioning. Gene expression profiling data were analyzed using Ingenuity Pathway Analysis. Real-time quantitative polymerase chain reaction analysis was used for single-gene validation. Luciferase reporter assay and argonaute 2 immunoprecipitation were performed for target validation.

RESULTS

MicroRNA-155 expression was significantly increased during the development of DAH. Disease progression was reduced in miR-155(-/-) mice as well as by in vivo silencing of miR-155 using a miR-155 antagomir. MicroRNA-155 silencing dampened pristane-induced ectopic activation of multiple inflammatory pathways and reduced the expression of proinflammatory cytokines. Several negative regulators of NF-κB signaling were inhibited by pristane and were reactivated in miR-155(-/-) mice. In particular, the antiinflammatory factor peroxisome proliferator-activated receptor α was identified as a direct target of miR-155.

CONCLUSION

MicroRNA-155 promotes pristane-induced lung inflammation. It contributes to ectopic activation of NF-κB signaling pathways by targeting multiple negative regulators. MicroRNA-155 antagomir may be a promising therapeutic strategy for treating acute lung inflammation in lupus.

Neutrophils Regulate Humoral Autoimmunity by Restricting Interferon-γ Production via the Generation of Reactive Oxygen Species

Here, we examine the mechanism by which plasmacytoid dendritic cells (pDCs) and type I interferons promote humoral autoimmunity. In an amyloid-induced experimental autoimmune model, neutrophil depletion enhanced anti-nuclear antibody development, which correlated with heightened IFN-γ production by natural killer (NK) cells. IFN-α/β produced by pDCs activated NK cells via IL-15 induction. Neutrophils released reactive oxygen species (ROS), which negatively modulated the levels of IL-15, thereby inhibiting IFN-γ production. Mice deficient in NADPH oxidase 2 produced increased amounts of IFN-γ and developed augmented titers of autoantibodies. Both the pDC-IFN-α/β pathway and IFN-γ were indispensable in stimulating humoral autoimmunity. Male NZB/W F1 mice expressed higher levels of superoxide than their female lupus-prone siblings, and depletion of neutrophils resulted in spontaneous NK cell and autoimmune B cell activation. Our findings suggest a regulatory role for neutrophils in vivo and highlight the importance of an NK-IFN-γ axis downstream of the pDC-IFN-α/β pathway in systemic autoimmunity.