Microvascular lung injury and endoplasmic reticulum stress in systemic lupus erythematosus-associated alveolar hemorrhage and pulmonary vasculitis.

Human COPA mutations affecting retrograde Golgi-to-endoplasmic reticulum (ER) protein transport cause diffuse alveolar hemorrhage (DAH) and ER stress ("COPA syndrome"). Patients with SLE also can develop DAH. C57BL/6 (B6) mice with pristane-induced lupus develop monocyte-dependent DAH indistinguishable from human DAH, whereas BALB/c mice are resistant. We examined Copa and ER stress in pristane-induced lupus. Copa expression, ER stress, vascular injury, and apoptosis were assessed in mice and COPA was quantified in blood from patients with SLE. Copa mRNA and protein expression were impaired in B6 mice with pristane-induced DAH, but not in pristane-treated BALB/c mice. An ER stress response (increased Hsp5a/BiP, Ddit3/CHOP, Eif2a, and spliced Xbp1) was seen in lungs from pristane-treated B6, but not BALB/c, mice. Resistance of BALB/c mice to DAH was overcome by treating them with low-dose thapsigargin plus pristane. CB6F1 mice did not develop DAH or ER stress, suggesting that susceptibility was recessive. Increased pulmonary expression of von Willebrand factor (Vwf), a marker of endothelial injury, and the chemokine Ccl2 in DAH suggested that pristane promotes lung microvascular injury and monocyte recruitment. Consistent with that possibility, lung endothelial cells and infiltrating bone marrow-derived cells from pristane-treated B6 mice expressed BiP and showed evidence of apoptosis (annexin-V and activated caspase-3 staining). COPA expression also was low in patients with SLE with lung involvement. Pristane-induced DAH may be initiated by endothelial injury, resulting in ER stress, apoptosis of lung endothelial cells, and recruitment of myeloid cells that propagate lung injury. The pathogenesis of DAH in SLE and COPA syndrome may overlap.

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.

A Novel Subset of Anti-Inflammatory CD138+ Macrophages Is Deficient in Mice with Experimental Lupus.

Dead cells accumulating in the tissues may contribute to chronic inflammation. We examined the cause of impaired apoptotic cell clearance in human and murine lupus. Dead cells accumulated in bone marrow from lupus patients but not from nonautoimmune patients undergoing myeloablation, where they were efficiently removed by macrophages (MΦ). Impaired apoptotic cell uptake by MΦ also was seen in mice treated i.p. with pristane (develop lupus) but not mineral oil (MO) (do not develop lupus). The inflammatory response to both pristane and MO rapidly depleted resident (Tim4+) large peritoneal MΦ. The peritoneal exudate of pristane-treated mice contained mainly Ly6Chi inflammatory monocytes; whereas in MO-treated mice, it consisted predominantly of a novel subset of highly phagocytic MΦ resembling small peritoneal MΦ (SPM) that expressed CD138+ and the scavenger receptor Marco. Treatment with anti-Marco-neutralizing Abs and the class A scavenger receptor antagonist polyinosinic acid inhibited phagocytosis of apoptotic cells by CD138+ MΦ. CD138+ MΦ expressed IL-10R, CD206, and CCR2 but little TNF-α or CX3CR1. They also expressed high levels of activated CREB, a transcription factor implicated in generating alternatively activated MΦ. Similar cells were identified in the spleen and lung of MO-treated mice and also were induced by LPS. We conclude that highly phagocytic, CD138+ SPM-like cells with an anti-inflammatory phenotype may promote the resolution of inflammation in lupus and infectious diseases. These SPM-like cells are not restricted to the peritoneum and may help clear apoptotic cells from tissues such as the lung, helping to prevent chronic inflammation.

"Lupoid hepatitis" in SLE patients and mice with experimental lupus.

The unusual subset of patients with severe hepatitis, hypergammaglobulinemia, arthritis, and LE cells in the blood reported by Henry Kunkel and others suggested to these investigators that "lupoid" hepatitis might share pathogenic mechanisms with SLE. More than half a century later, the etiology of autoimmune hepatitis remains unclear. The occurrence of autoimmune hepatitis in a small fraction (about 3%) of SLE patients in our lupus cohort and in two mouse models of SLE supports their conclusion that lupoid hepatitis may be share pathogenic mechanisms with SLE. The development of autoimmune hepatitis in mice with pristane-induced lupus provides an opportunity to further explore the potential link between these two autoimmune disorders.

Serum autoantibodies in pristane induced lupus are regulated by neutrophil gelatinase associated lipocalin.

The onset of autoantibodies in systemic autoimmunity can be the result of a breakdown in tolerance at multiple checkpoints. Genetic, hormonal, and immunological factors can combine with environmental influences to accelerate the onset of disease and aggravate disease outcome. Here, we describe a novel mechanism relating to the regulatory role of Neutrophil Gelatinase Associated Lipocalin (NGAL) in modulating the levels of autoantibodies in pristane induced lupus. Following a single injection of pristane intraperitoneally, NGAL expression was induced in both the serum and spleen. Furthermore, NGAL deficient mice were more susceptible to the induction of pristane stimulated autoimmunity, and displayed higher numbers of autoantibody secreting cells and increased expression of activation induced cytidine deaminase (AID) and other inflammatory mediators in the spleen. In contrast, kidney damage was milder in NGAL deficient mice, indicating that NGAL was detrimental in autoantibody mediated kidney disease. These studies indicate that NGAL plays differential roles in different tissues in the context of lupus, and suggest a previously unrecognized role for NGAL in adaptive immunity.

Pleiotropic IFN-dependent and -independent effects of IRF5 on the pathogenesis of experimental lupus.

Genetic polymorphisms of IFN regulatory factor 5 (IRF5) are associated with an increased risk of lupus in humans. In this study, we examined the role of IRF5 in the pathogenesis of pristane-induced lupus in mice. The pathological response to pristane in IRF5(-/-) mice shared many features with type I IFN receptor (IFNAR)(-/-) and TLR7(-/-) mice: production of anti-Sm/RNP autoantibodies, glomerulonephritis, generation of Ly6C(hi) monocytes, and IFN-I production all were greatly attenuated. Lymphocyte activation following pristane injection was greatly diminished in IRF5(-/-) mice, and Th cell differentiation was deviated from Th1 in wild-type mice toward Th2 in IRF5(-/-) mice. Th cell development was skewed similarly in TLR7(-/-) or IFNAR(-/-) mice, suggesting that IRF5 alters T cell activation and differentiation by affecting cytokine production. Indeed, production of IFN-I, IL-12, and IL-23 in response to pristane was markedly decreased, whereas IL-4 increased. Unexpectedly, plasmacytoid dendritic cells (pDC) were not recruited to the site of inflammation in IRF5(-/-) or MyD88(-/-) mice, but were recruited normally in IFNAR(-/-) and TLR7(-/-) mice. In striking contrast to wild-type mice, pristane did not stimulate local expression of CCL19 and CCL21 in IRF5(-/-) mice, suggesting that IRF5 regulates chemokine-mediated pDC migration independently of its effects on IFN-I. Collectively, these data indicate that altered production of IFN-I and other cytokines in IRF5(-/-) mice prevents pristane from inducing lupus pathology by broadly affecting T and B lymphocyte activation/differentiation. Additionally, we uncovered a new, IFN-I-independent role of IRF5 in regulating chemokines involved in the homing of pDCs and certain lymphocyte subsets.

MEK1/2 and ERK1/2 mediated lung endothelial injury and altered hemostasis promote diffuse alveolar hemorrhage in murine lupus.

Objective: About 3% of lupus patients develop severe diffuse alveolar hemorrhage (DAH) with pulmonary vasculitis. B6 mice with pristane-induced lupus also develop DAH, but BALB/c mice are resistant. DAH is independent of TLR signaling and other inflammatory pathways. This study examined the role of the mitogen-activated protein kinase pathway (MEK1/2-ERK1/2, JNK, p38). Methods: B6 and BALB/c mice were treated with pristane ± inhibitors of MEK1/2 (trametinib/GSK1120212, "GSK"), ERK1/2 (SCH772984, "SCH"), JNK, or p38. Effects on lung hemorrhage and hemostasis were determined. Results: GSK and SCH abolished DAH, whereas JNK and p38 inhibitors were ineffective. Apoptotic cells were present in lung from pristane-treated mice, but not mice receiving pristane+GSK and endothelial dysfunction was normalized. Expression of the ERK1/2-regulated transcription factor Egr1 increased in pristane-treated B6, but not BALB/c, mice and was normalized by GSK. Pristane also increased expression of the anticoagulant genes Tfpi (tissue factor pathway inhibitor) and Thbd (thrombomodulin) in B6 mice. The ratio of tissue factor ( F3 ) to Tfpi increased in B6 (but not BALB/c) mice and was normalized by GSK. Circulating Thbd protein increased in B6 mice and returned to normal after GSK treatment. Consistent with augmented endothelial anticoagulant activity, pristane treatment increased tail bleeding in B6 mice. Conclusion: Pristane treatment promotes lung endothelial injury and DAH in B6 mice by activating the MEK1/2-ERK1/2 pathway and impairing hemostasis. The hereditary factors determining susceptibility to lung injury and bleeding in pristane-induced lupus are relevant to the pathophysiology of life-threatening DAH in SLE and may help to optimize therapy.

MEK1/2 and ERK1/2 mediated lung endothelial injury and altered hemostasis promote diffuse alveolar hemorrhage in murine lupus.

OBJECTIVE: About 3% of lupus patients develop severe diffuse alveolar hemorrhage (DAH) with pulmonary vasculitis. B6 mice with pristane-induced lupus also develop DAH, but BALB/c mice are resistant. DAH is independent of TLR signaling and other inflammatory pathways. This study examined the role of the mitogen-activated protein kinase pathway (MEK1/2-ERK1/2, JNK, p38). METHODS: B6 and BALB/c mice were treated with pristane ± inhibitors of MEK1/2 (trametinib/GSK1120212, "GSK"), ERK1/2 (SCH772984, "SCH"), JNK, or p38. Effects on lung hemorrhage and hemostasis were determined. RESULTS: GSK and SCH abolished DAH, whereas JNK and p38 inhibitors were ineffective. Apoptotic cells were present in lung from pristane-treated mice, but not mice receiving pristane+GSK and endothelial dysfunction was normalized. Expression of the ERK1/2-regulated transcription factor Egr1 increased in pristane-treated B6, but not BALB/c, mice and was normalized by GSK. Pristane also increased expression of the anticoagulant genes Tfpi (tissue factor pathway inhibitor) and Thbd (thrombomodulin) in B6 mice. The ratio of tissue factor (F3) to Tfpi increased in B6 (but not BALB/c) mice and was normalized by GSK. Circulating Thbd protein increased in B6 mice and returned to normal after GSK treatment. Consistent with augmented endothelial anticoagulant activity, pristane treatment increased tail bleeding in B6 mice. CONCLUSION: Pristane treatment promotes lung endothelial injury and DAH in B6 mice by activating the MEK1/2-ERK1/2 pathway and impairing hemostasis. The hereditary factors determining susceptibility to lung injury and bleeding in pristane-induced lupus are relevant to the pathophysiology of life-threatening DAH in SLE and may help to optimize therapy.

PROTAC-mediated NR4A1 degradation as a novel strategy for cancer immunotherapy.

An effective cancer therapy requires killing cancer cells and targeting the tumor microenvironment (TME). Searching for molecules critical for multiple cell types in the TME, we identified NR4A1 as one such molecule that can maintain the immune suppressive TME. Here, we establish NR4A1 as a valid target for cancer immunotherapy and describe a first-of-its-kind proteolysis-targeting chimera (PROTAC, named NR-V04) against NR4A1. NR-V04 degrades NR4A1 within hours in vitro and exhibits long-lasting NR4A1 degradation in tumors with an excellent safety profile. NR-V04 inhibits and frequently eradicates established tumors. At the mechanistic level, NR-V04 induces the tumor-infiltrating (TI) B cells and effector memory CD8+ T (Tem) cells and reduces monocytic myeloid-derived suppressor cells (m-MDSC), all of which are known to be clinically relevant immune cell populations in human melanomas. Overall, NR-V04-mediated NR4A1 degradation holds promise for enhancing anticancer immune responses and offers a new avenue for treating various types of cancers such as melanoma.

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.

CD177 modulates the function and homeostasis of tumor-infiltrating regulatory T cells.

Regulatory T (Treg) cells are one of the major immunosuppressive cell types in cancer and a potential target for immunotherapy, but targeting tumor-infiltrating (TI) Treg cells has been challenging. Here, using single-cell RNA sequencing of immune cells from renal clear cell carcinoma (ccRCC) patients, we identify two distinct transcriptional fates for TI Treg cells, Fate-1 and Fate-2. The Fate-1 signature is associated with a poorer prognosis in ccRCC and several other solid cancers. CD177, a cell surface protein normally expressed on neutrophil, is specifically expressed on Fate-1 TI Treg cells in several solid cancer types, but not on other TI or peripheral Treg cells. Mechanistically, blocking CD177 reduces the suppressive activity of Treg cells in vitro, while Treg-specific deletion of Cd177 leads to decreased tumor growth and reduced TI Treg frequency in mice. Our results thus uncover a functional CD177+ TI Treg population that may serve as a target for TI Treg-specific immunotherapy.

NF-E2-Related Factor 2 Regulates Interferon Receptor Expression and Alters Macrophage Polarization in Lupus.

OBJECTIVE: Pristane-induced lupus is associated with nonresolving inflammation and deficiency of proresolving macrophages. Proresolving nonclassic macrophages (NCMs) are less responsive to type I interferon (IFN) than classic macrophages (CMs; which are proinflammatory), reflecting their relative expression levels of the type I IFN receptor (IFNAR). This study was undertaken to investigate the regulation of IFNAR expression in macrophages. METHODS: We carried out gene expression profiling of purified CMs and NCMs from mice treated with pristane (which develop lupus) or mineral oil (non-lupus controls). Macrophage differentiation and IFNAR expression were examined in mice treated with NF-E2-related factor 2 (Nrf2) activators and inhibitors and in Nrf2-deficient mice. Nrf2 activity was also assessed in blood cells from patients with systemic lupus erythematosus (SLE). Significant differences were determined by Student's t-test. RESULTS: RNA sequencing revealed increased expression of genes regulated by the transcription factor Nrf2 in NCMs from mineral oil-treated versus pristane-treated mice and in NCMs versus CMs. The Nrf2 activator CDDO-imidazole (CDDO-Im) decreased CMs (P < 0.0001) and promoted the development of proresolving NCMs (P = 0.06), whereas the Nrf2 inhibitor brusatol increased CMs (P < 0.05) and decreased NCMs (P < 0.001). CDDO-Im decreased Ifnar1 (P < 0.001) and IFN-stimulated gene (ISG) expression in macrophages and alleviated oxidative stress (P < 0.05), whereas brusatol had the opposite effect (P < 0.01). Moreover, Ifnar1 and ISG expression levels were higher in Nrf2-knockout mice than controls (P < 0.05). As seen in mice with lupus, SLE patients showed evidence of low Nrf2 activity. CONCLUSION: Our findings indicate that Nrf2 activation favors the resolution of chronic inflammation in lupus. Since autoantibody production and lupus nephritis depend on IFNAR signaling, the ability of Nrf2 activators to repolarize macrophages and reduce the INF signature suggests that these agents may warrant consideration for treating lupus.

Differential Responsiveness of Monocyte and Macrophage Subsets to Interferon.

OBJECTIVE: Peripheral blood mononuclear cells (PBMCs) in systemic lupus erythematosus (SLE) patients exhibit a gene expression program (interferon [IFN] signature) that is attributed to overproduction of type I IFNs by plasmacytoid dendritic cells. Type I IFNs have been thought to play a role in the pathogenesis of SLE. This study was undertaken to examine an unexpected influence of monocyte/macrophages on the IFN signature. METHODS: Proinflammatory (classic) and antiinflammatory (nonclassic) monocyte/macrophages were sorted from mice and analyzed by RNA sequencing and quantitative polymerase chain reaction (qPCR). Type I IFN-α/ß/ω receptor (IFNAR-1) expression was determined by qPCR and flow cytometry. Macrophages were stimulated in vitro with IFNα, and pSTAT1was measured. RESULTS: Transcriptional profiling of peritoneal macrophages from mice with pristane-induced SLE unexpectedly indicated a strong IFN signature in classic, but not nonclassic, monocyte/macrophages exposed to the same type I IFN concentrations. Ifnar1 messenger RNA and IFNAR surface staining were higher in classic monocyte/macrophages versus nonclassic monocyte/macrophages (P < 0.0001 and P < 0.05, respectively, by Student's t-test). Nonclassic monocyte/macrophages were also relatively insensitive to IFNα-driven STAT1 phosphorylation. Humans exhibited a similar pattern: higher IFNAR expression (P < 0.0001 by Student's t-test) and IFNα-stimulated gene expression (P < 0.01 by paired Wilcoxon's rank sum test) in classic monocyte/macrophages and lower levels in nonclassic monocyte/macrophages. CONCLUSION: This study revealed that the relative abundance of different monocyte/macrophage subsets helps determine the magnitude of the IFN signature. Responsiveness to IFNα signaling reflects differences in IFNAR expression in classic (high IFNAR) compared to nonclassic (low IFNAR) monocyte/macrophages. Thus, the IFN signature depends on both type I IFN production and the responsiveness of monocyte/macrophages to IFNAR signaling.

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.

Liver X Receptor Agonist Therapy Prevents Diffuse Alveolar Hemorrhage in Murine Lupus by Repolarizing Macrophages.

The generation of CD138+ phagocytic macrophages with an alternative (M2) phenotype that clear apoptotic cells from tissues is defective in lupus. Liver X receptor-alpha (LXRα) is an oxysterol-regulated transcription factor that promotes reverse cholesterol transport and alternative (M2) macrophage activation. Conversely, hypoxia-inducible factor 1-α (HIF1α) promotes classical (M1) macrophage activation. The objective of this study was to see if lupus can be treated by enhancing the generation of M2-like macrophages using LXR agonists. Peritoneal macrophages from pristane-treated mice had an M1 phenotype, high HIFα-regulated phosphofructokinase and TNFα expression (quantitative PCR, flow cytometry), and low expression of the LXRα-regulated gene ATP binding cassette subfamily A member 1 (Abca1) and Il10 vs. mice treated with mineral oil, a control inflammatory oil that does not cause lupus. Glycolytic metabolism (extracellular flux assays) and Hif1a expression were higher in pristane-treated mice (M1-like) whereas oxidative metabolism and LXRα expression were higher in mineral oil-treated mice (M2-like). Similarly, lupus patients' monocytes exhibited low LXRα/ABCA1 and high HIF1α vs. CONTROLS: The LXR agonist T0901317 inhibited type I interferon and increased ABCA1 in lupus patients' monocytes and in murine peritoneal macrophages. In vivo, T0901317 induced M2-like macrophage polarization and protected mice from diffuse alveolar hemorrhage (DAH), an often fatal complication of lupus. We conclude that end-organ damage (DAH) in murine lupus can be prevented using an LXR agonist to correct a macrophage differentiation abnormality characteristic of lupus. LXR agonists also decrease inflammatory cytokine production by human lupus monocytes, suggesting that these agents may be have a role in the pharmacotherapy of 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.

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.

Mechanisms of autoantibody production in systemic lupus erythematosus.

Autoantibodies against a panoply of self-antigens are seen in systemic lupus erythematosus, but only a few (anti-Sm/RNP, anti-Ro/La, anti-dsDNA) are common. The common lupus autoantigens are nucleic acid complexes and levels of autoantibodies can be extraordinarily high. We explore why that is the case. Lupus is associated with impaired central or peripheral B-cell tolerance and increased circulating autoreactive B cells. However, terminal differentiation is necessary for autoantibody production. Nucleic acid components of the major lupus autoantigens are immunostimulatory ligands for toll-like receptor (TLR)7 or TLR9 that promote plasma cell differentiation. We show that the levels of autoantibodies against the U1A protein (part of a ribonucleoprotein) are markedly higher than autoantibodies against other antigens, including dsDNA and the non-nucleic acid-associated autoantigens insulin and thyroglobulin. In addition to driving autoantibody production, TLR7 engagement is likely to contribute to the pathogenesis of inflammatory disease in lupus.