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

Pericardial and mediastinal fat-associated lymphoid clusters are rapidly activated in an alkane-induced model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease predominated by auto-antibodies that recognise cellular components. Pleural involvement is the most common SLE-related lung disease. Natural antibodies are rapidly secreted by innate-like B cells following perturbation of homeostasis and are important in the early stages of immune activation. The serous cavities are home to large numbers of innate-like B cells present both within serous fluid and resident within fat-associated lymphoid clusters (FALCs). FALCs are important hubs for B-cell activation and local antibody secretion within the body cavities. Patients with SLE can develop anti-phospholipid antibodies and in rare situations develop alveolar haemorrhage. Utilising delivery of the hydrocarbon oil pristane in C57BL/6 mice as a model of SLE we identify a rapid expansion of pleural cavity B cells as early as day 3 after intra-peritoneal pristane delivery. Following pristane delivery, pericardial B1 B cells are proliferative, express the plasma-cell surface marker CD138, and secrete both innate and class-switched antibodies highlighting that this cavity niche may play an unrecognised role in the initiation of lupus pleuritis.

The complement system and human autoimmune diseases

Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.

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.

IgM anti-phosphorylcholine antibodies associate with senescent and IL-17+ T cells in SLE patients with a pro-inflammatory lipid profile

OBJECTIVE

The aim was to evaluate whether T cell subsets and the lipid profile could be linked to the cardioprotective effect of IgM anti-phosphorylcholine (PC) antibodies in SLE.

METHODS

Anti-PC antibodies were quantified by ELISA in 197 patients and 99 controls and analysed in relationship to clinical features, treatments and serum lipids. Carotid atheromatosis was evaluated by ultrasonography; Th1, Th17, Treg and CD4+CD28null cells by flow cytometry; and cytokine serum levels by immunoassays, in a subgroup of 120 SLE patients and 33 controls.

RESULTS

IgM anti-PC serum levels were reduced in SLE patients compared with controls (P < 0.001) and were associated with age (β= -0.252; P = 0.002), high-density lipoprotein (HDL; β = 0.271; P = 0.001), low-density lipoprotein (LDL; β= -0.192; P = 0.017) and glucocorticoid treatment (β= -0.201; P = 0.012), whereas the IgG-to-IgM anti-PC ratio was increased (P = 0.007) and associated with age (β = 0.194; P = 0.028) and SLEDAI (β = 0.250; P = 0.005). Also, patients with clinical or subclinical cardiovascular disease exhibited reduced IgM anti-PC levels compared with their cardiovascular disease-free counterparts, regardless of glucocorticoid usage (P = 0.001). CD4+CD28null and Th17 cells were increased in SLE patients compared with controls (P < 0.01) and correlated inversely with IgM anti-PC levels. These associations were observed in patients displaying high triglyceride or low HDL levels, even after adjusting for clinical parameters and treatments (CD4+CD28null: β = -0.455, P = 0.001; Th17: β= -0.280, P = 0.035), but not in those with a normal lipid profile. High triglyceride and low HDL profiles were related to low IgM anti-PC and Treg levels, respectively, whereas both lipid profiles were associated with inflammatory markers and cytokines.

CONCLUSION

The present study provides evidence for an association of IgM anti-PC antibodies with pro-atherogenic T cell subsets in SLE, with a high triglyceride/low HDL lipid profile playing a facilitating major role.

NOX2 mediates quiescent handling of dead cell remnants in phagocytes

The phagocyte NADPH oxidase (the NOX2 complex) generates superoxide, the precursor to reactive oxygen species (ROS). ROS possess both antimicrobial and immunoregulatory function. Inactivating mutations in alleles of the NOX2 complex cause chronic granulomatous disease (CGD), characterized by an enhanced susceptibility to infections and autoimmune diseases such as Systemic lupus erythematosus (SLE). The latter is characterized by insufficient removal of dead cells, resulting in an autoimmune response against components of the cell's nucleus when non-cleared apoptotic cells lose their membrane integrity and present autoantigenic molecules in an inflammatory context. Here we aimed to shed light on the role of the NOX2 complex in handling of secondary necrotic cells (SNECs) and associated consequences for inflammation and autoimmunity during lupus.

We show that individuals with SLE and CGD display accumulation of SNECs in blood monocytes and neutrophils. In a CGD phenotypic mouse strain (Ncf1** mice) build-up of SNECs in Ly6C^HI blood monocytes was connected with a delayed degradation of the phagosomal cargo and accompanied by production of inflammatory mediators. Treatment with H₂O₂ or activators of ROS-formation reconstituted phagosomal abundance of SNECs to normal levels. Induction of experimental lupus further induced increased antibody-dependent uptake of SNECs into neutrophils. Lupus-primed Ncf1** neutrophils took up more SNECs than wild type neutrophils, whereas SNEC-accumulation in regulatory Ly6C^−/LO monocytes was lower in Ncf1**mice. We deduce that the inflammatory rerouting of immune-stimulatory necrotic material into inflammatory phagocyte subsets contributes to the connection between low ROS production by the NOX2 complex and SLE.

Missing in action-The meaning of cell death in tissue damage and inflammation

Billions of cells die every day in higher organisms as part of the normal process of tissue homeostasis. During special conditions like in development, acute infections, mechanical injuries, and immunity, cell death is a common denominator and it exerts profound effects in the outcome of these scenarios. To prevent the accumulation of aged, superfluous, infected, damaged and dead cells, professional phagocytes act in a rapid and efficient manner to clear the battle field and avoid spread of the destruction. Neutrophils are the most abundant effector immune cells that extravasate into tissues and can turn injured tissues into gory battle fields. In peace times, neutrophils tend to patrol tissues without provoking inflammatory reactions. We discuss in this review actual and forgotten knowledge about the meaning of cell death during homeostatic processes and drive the attention to the importance of the action of neutrophils during patrolling and for the maintenance or recovery of the homeostatic state once the organism gets attacked or injured, respectively. In this fashion, we disclose several disease conditions that arise as collateral damage of physiological responses to death.

The Evolving Landscape for Complement Therapeutics in Rheumatic and Autoimmune Diseases

The complement system is increasingly understood to play major roles in the pathogenesis of human inflammatory and autoimmune diseases. Because of this situation, there are rapidly expanding commercial efforts to develop novel complement inhibitors and effector pathway-modulating drugs. This review provides insights into the evolving understanding of the complement system components, mechanisms of activation within and across the 3 pathways (classical, alternative, and lectin), how the pathways are normally controlled and then dysregulated in target tissues, and what diseases are known to be, in large part, complement-dependent through the successful development and approval of complement therapeutics in patients. Mechanisms of complement activation in rheumatoid arthritis, lupus, and thrombotic microangiopathies are also illustrated. In addition, the specific therapeutic drugs that are both approved and under development are discussed in the context of both nonrheumatic and rheumatic diseases. Finally, the methods by which the complement system can be assessed in humans through biomarker studies are outlined, with the goal of understanding, in specific patients, how the system is functioning.

Pristane-induced lupus: considerations on this experimental model

Systemic lupus erythematosus (SLE) is a multifactorial, autoimmune inflammatory disease with pleomorphic clinical manifestations involving different organs and tissues. The etiology of this disease has been associated with a dysfunctional response of B and T lymphocytes against environmental stimuli in individuals genetically susceptible to SLE, which determines an immune response against different autoantigens and, consequently, tissue damage. The study of different murine models has provided a better understanding of these autoimmune phenomena. This review primarily focuses on that has been learned from the pristane-induced lupus (PIL) model and how this model can be used to supplement recent advances in understanding the pathogenesis of SLE. We also consider both current and future therapies for this disease. The PubMed, SciELO, and Embase databases were searched for relevant articles published from 1950 to 2016. PIL has been shown to be a useful tool for understanding the multiple mechanisms involved in systemic autoimmunity. In addition, it can be considered an efficient model to evaluate the environmental contributions and interferon signatures present in patients with SLE.

The Microbiome in Connective Tissue Diseases and Vasculitides: An Updated Narrative Review

Objective

To provide a narrative review of the most recent data concerning the involvement of the microbiome in the pathogenesis of connective tissue diseases (CTDs) and vasculitides.

Methods

The PubMed database was searched for articles using combinations of words or terms that included systemic lupus erythematosus, systemic sclerosis, autoimmune myositis, Sjögren's syndrome, undifferentiated and mixed CTD, vasculitis, microbiota, microbiome, and dysbiosis. Papers from the reference lists of the articles and book chapters were reviewed, and relevant publications were identified. Abstracts and articles written in languages other than English were excluded.

Results

We found some evidence that dysbiosis participates in the pathogenesis of systemic lupus erythematosus, systemic sclerosis, Sjögren's syndrome, and Behçet's disease, but there are still few data concerning the role of dysbiosis in other CTDs or vasculitides.

Conclusions

Numerous studies suggest that alterations in human microbiota may be involved in the pathogenesis of inflammatory arthritides as a result of the aberrant activation of the innate and adaptive immune responses. Only a few studies have explored the involvement of dysbiosis in other CTDs or vasculitides, and further research is needed.

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 Ly6C^hi 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.

Recent advances in the understanding of renal inflammation and fibrosis in lupus nephritis

Lupus nephritis is a potentially reversible cause of severe acute kidney injury and is an important cause of end-stage renal failure in Asians and patients of African or Hispanic descent. It is characterized by aberrant exaggerated innate and adaptive immune responses, autoantibody production and their deposition in the kidney parenchyma, triggering complement activation, activation and proliferation of resident renal cells, and expression of pro-inflammatory and chemotactic molecules leading to the influx of inflammatory cells, all of which culminate in destruction of normal nephrons and their replacement by fibrous tissue. Anti-double-stranded DNA (anti-dsDNA) antibody level correlates with disease activity in most patients. There is evidence that apart from mediating pathogenic processes through the formation of immune complexes, pathogenic anti-dsDNA antibodies can bind to resident renal cells and induce downstream pro-apoptotic, pro-inflammatory, or pro-fibrotic processes or a combination of these. Recent data also highlight the critical role of macrophages in acute and chronic kidney injury. Though clinically effective, current treatments for lupus nephritis encompass non-specific immunosuppression and the anti-inflammatory action of high-dose corticosteroids. The clinical and histological impact of novel biologics targeting pro-inflammatory molecules remains to be investigated. Insight into the underlying mechanisms that induce inflammatory and fibrotic processes in the kidney of lupus nephritis could present opportunities for more specific novel treatment options to improve clinical outcomes while minimizing off-target untoward effects. This review discusses recent advances in the understanding of pathogenic mechanisms leading to inflammation and fibrosis of the kidney in lupus nephritis in the context of established standard-of-care and emerging therapies.

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.

Annexin II-binding immunoglobulins in patients with lupus nephritis and their correlation with disease manifestations

Annexin II on mesangial cell surface mediates the binding of anti-dsDNA antibodies and consequent downstream inflammatory and fibrotic processes. We investigated the clinical relevance of circulating annexin II-binding immunoglobulins (Igs) in patients with severe proliferative lupus nephritis, and renal annexin II expression in relation to progression of nephritis in New Zealand Black and White F1 mice (NZBWF1/J) mice. Annexin II-binding Igs in serum were measured by ELISA. Ultrastructural localization of annexin II was determined by electron microscopy. Seropositivity rates for annexin II-binding IgG and IgM in patients with active lupus nephritis were significantly higher compared with controls (8.9%, 1.3% and 0.9% for annexin II-binding IgG and 11.1%, 4.0% and 1.9% for annexin II-binding IgM for patients with active lupus nephritis, patients with non-lupus renal disease and healthy subjects respectively). In lupus patients, annexin II-binding IgM level was higher at disease flare compared with remission. Annexin II-binding IgG and IgM levels were associated with that of anti-dsDNA and disease activity. Annexin II-binding IgG and IgM levels correlated with histological activity index in lupus nephritis biopsy samples. In NZBWF1/J mice, serum annexin II-binding IgG and IgM levels and glomerular annexin II and p11 expression increased with progression of active nephritis. Annexin II expression was present on mesangial cell surface and in the mesangial matrix, and co-localized with electron-dense deposits along the glomerular basement membrane. Our results show that circulating annexin II-binding IgG and IgM levels are associated with clinical and histological disease activity in proliferative lupus nephritis. The co-localization of annexin II and p11 expression with immune deposition in the kidney suggests pathogenic relevance.

"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.