Effects of complement factor D deficiency on the renal disease of MRL/lpr mice

Balancing efficacy and safety of complement inhibitors

Complement inhibitors have been approved for several immune-mediated diseases and they are considered the next paradigm-shifting approach in the treatment of glomerulonephritis. The hierarchical organization of the complement system offers numerous molecular targets for therapeutic intervention. However, complement is an integral element of host defense and therefore complement inhibition can be associated with serious infectious complications. Here we give a closer look to the hierarchical complement system and how interfering with proximal versus distal or selective versus unselective molecular targets could determine efficacy and safety. Furthermore, we propose to consider the type of disease, immunological activity, and patient immunocompetence when stratifying patients, e.g., proximal/unselective targets for highly active and potentially fatal diseases while distal and selective targets may suit more chronic disease conditions with low or moderate disease activity requiring persistent complement blockade in patients with concomitant immunodeficiency. Certainly, there exists substantial promise for anti-complement therapeutics. However, balancing efficacy and safety will be key to establish powerful treatment effects with minimal adverse events, especially when complement blockade is continued over longer periods of time in chronic disorders.

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

The Role of Adipsin, Complement Factor D, in the Pathogenesis of Graves' Orbitopathy

Purpose

Graves' orbitopathy (GO) is an orbital manifestation of autoimmune Graves' disease, and orbital fibroblast is considered a target cell, producing pro-inflammatory cytokines and/or differentiating into adipocytes. Adipose tissue has been focused on as an endocrine and inflammatory organ secreting adipokines. We investigated the pathogenic role of a specific adipokine, adipsin, known as complement factor D in Graves' orbital fibroblasts.

Methods

The messenger RNA (mRNA) expression of multiple adipokines was investigated in adipose tissues harvested from GO and healthy subjects. Adipsin protein production was analyzed in primary cultured orbital fibroblasts under insulin growth factor (IGF)-1, CD40 ligand (CD40L) stimulation, and adipogenesis. The effect of blocking adipsin with small interfering RNA (siRNA) on pro-inflammatory cytokine production and adipogenesis was evaluated using quantitative real-time PCR, Western blot, and ELISA. Adipogenic differentiation was identified using Oil Red O staining.

Results

Adipsin gene expression was significantly elevated in GO tissue and increased after the stimulation of IGF-1 and CD40L, as well as adipocyte differentiation in GO cells. Silencing of adipsin suppressed IGF-1-induced IL-6, IL-8, COX2, ICAM-1, CCL2 gene expression, and IL-6 protein secretion. Adipsin suppression also attenuated adipocyte differentiation. Exogenous treatment of recombinant adipsin resulted in the activation of the Akt, ERK, p-38, and JNK signaling pathways.

Conclusions

Adipsin, secreted by orbital fibroblasts, may play a distinct role in the pathogenesis of GO. Inhibition of adipsin ameliorated the production of pro-inflammatory cytokines and adipogenesis in orbital fibroblasts. Our study provides an in vitro basis suggesting adipsin as a potential therapeutic target for GO treatment.

Complement therapeutics are coming of age in rheumatology

The complement system was described over 100 years ago, and it is well established that activation of this pathway accompanies the great majority of autoimmune and inflammatory diseases. In addition, over three decades of work in murine models of human disease have nearly universally demonstrated that complement activation is upstream of tissue injury and the engagement of pro-inflammatory mechanisms such as the elaboration of cytokines and chemokines, as well as myeloid cell recruitment and activation. With that background, and taking advantage of advances in the development of biologic and small-molecule therapeutics, the creation and clinical evaluation of complement therapeutics is now rapidly expanding. This article reviews the current state of the complement therapeutics field, with a focus on their use in diseases cared for or consulted upon by rheumatologists. Included is an overview of the activation mechanisms and components of the system, in addition to the mechanisms by which the complement system interacts with other immune system constituents. The various therapeutic approaches to modulating the system in rheumatic and autoimmune diseases are reviewed. To understand how best to clinically assess the complement system, methods of its evaluation are described. Finally, next-generation therapeutic and diagnostic advances that can be envisioned for the future are discussed.

Contributions of animal models to mechanistic understandings of antibody-dependent disease and roles of the amplification loop

The complement system plays an important pathophysiologic role in human diseases associated with immune or ischemic insults. In addition to understanding the effector mechanisms that are important for the biological effects of the system, substantial efforts have gone into understanding which specific complement activation pathways generate these potent effects. These approaches include the use of gene-targeted mice and specific pathway inhibitors, as well as the integration of human disease genetic and biomarker studies. In some disease states, it is quite clear that the alternate pathway plays a unique role in the initiation of the complement system. However, although initially a widely unexpected finding, it has now been shown in many tissue-based disease models and in initial human studies that engagement of the amplification loop is also essential for tissue injury when the classical and/or lectin pathways initiate pathway activation through pathogenic autoantibodies. This review provides evidence for such a conclusion through animal models, focusing on pathogenic antibody passive transfer models but also other relevant experimental systems. These data, along with initial biomarkers and clinical trial outcomes in human diseases that are associated with pathogenic autoantibodies, suggest that targeting the alternative pathway amplification loop may have near-universal therapeutic utility for tissue-based diseases.

Low-molecular weight inhibitors of the alternative complement pathway

Dysregulation of the alternative complement pathway predisposes individuals to a number of diseases. It can either be evoked by genetic alterations in or by stabilizing antibodies to important pathway components and typically leads to severe diseases such as paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, C3 glomerulopathy, and age-related macular degeneration. In addition, the alternative pathway may also be involved in many other diseases where its amplifying function for all complement pathways might play a role. To identify specific alternative pathway inhibitors that qualify as therapeutics for these diseases, drug discovery efforts have focused on the two central proteases of the pathway, factor B and factor D. Although drug discovery has been challenging for a number of reasons, potent and selective low-molecular weight (LMW) oral inhibitors have now been discovered for both proteases and several molecules are in clinical development for multiple complement-mediated diseases. While the clinical development of these inhibitors initially focuses on diseases with systemic and/or peripheral tissue complement activation, the availability of LMW inhibitors may also open up the prospect of inhibiting complement in the central nervous system where its activation may also play an important role in several neurodegenerative diseases.

Kidney diseases

Dysregulation and accelerated activation of the alternative pathway (AP) of complement is known to cause or accentuate several pathologic conditions in which kidney injury leads to the appearance of hematuria and proteinuria and ultimately to the development of chronic renal failure. Multiple genetic and acquired defects involving plasma- and membrane-associated proteins are probably necessary to impair the protection of host tissues and to confer a significant predisposition to AP-mediated kidney diseases. This review aims to explore how our current understanding will make it possible to identify the mechanisms that underlie AP-mediated kidney diseases and to discuss the available clinical evidence that supports complement-directed therapies. Although the value of limiting uncontrolled complement activation has long been recognized, incorporating complement-targeted treatments into clinical use has proved challenging. Availability of anti-complement therapy has dramatically transformed the outcome of atypical hemolytic uremic syndrome, one of the most severe kidney diseases. Innovative drugs that directly counteract AP dysregulation have also opened new perspectives for the management of other kidney diseases in which complement activation is involved. However, gained experience indicates that the choice of drug should be tailored to each patient's characteristics, including clinical, histologic, genetic, and biochemical parameters. Successfully treating patients requires further research in the field and close collaboration between clinicians and researchers who have special expertise in the complement system.

Thrombotic microangiopathy mediates poor prognosis among lupus nephritis via complement lectin and alternative pathway activation

Objective

The pathogenesis of thrombotic microangiopathy (TMA) in lupus nephritis (LN) remains complicated. This study aimed to detect the deposition of complement lectin pathway (LP) and alternative pathway (AP) components in renal tissues, then evaluate the clinicopathological characteristics and risk factors for renal survival between patients with or without TMA in LN cohorts.

Methods

We included 79 patients with biopsy-proven LN-associated TMA and matched the same number of LN patients without TMA as the control group. The deposition of mannose binding lectin (MBL), MBL-associated serine proteases 1/3 (MASP1/3), complement factor B (CFB), complement factor D (CFD), C4d, and von Willebrand factor (VWF) in renal tissue was assessed by immunohistochemistry and immunofluorescence. Besides, co-localization of C5b-9 and CD34 was detected by confocal microscopy.

Results

In our retrospective cohort, the incidence of acute kidney injury (30% vs. 14%, p = 0.013), acute hemodialysis (35% vs. 5%, p < 0.001), and interstitial fibrosis (43% vs. 13%, p < 0.001) is higher in the TMA, compared with the control group. Despite aggressive steroids pulse, plasma exchange, and immunosuppressive therapy among TMA group, they still had significantly inferior 3-year renal survival rates (68% vs. 89%, p = 0.002) than those in the non-TMA group. COX regression analysis identified that TMA (HR 4.807, 95% CI [2.052, 11.263], p < 0.001) is a risk factor in LN. MBL, MASP1/3, CFB, CFD, C4d, and VWF deposited along the glomerulus among LN, while TMA had stronger staining intensity and deposition. The co-localized expression of CD34 and C5b-9 in the endothelial cells was also observed in the renal tissues.

Conclusions

TMA is an independent risk factor for renal survival in LN patients. Moreover, LP and AP activation are involved in the pathogenesis of LN-associated TMA.

Predictive factors for the development of lupus nephritis after diagnosis of systemic lupus erythematosus

OBJECTIVES

To determine predictive factors for the development of lupus nephritis (LN) at the time of diagnosis of systemic lupus erythematosus (SLE).

METHODS

A case-control study was carried out in a single center, 595 patients with a diagnosis of SLE without LN participated by clinical or laboratory parameters at diagnosis, they were followed for a mean of 6.8 (+4.5) years, conforming to the data of their files two groups: with NL (cases) and without NL (controls) at the end of the follow-up. Sociodemographic, clinical, serological, immunological variables and the albumin - globulin ratio (AGR), calculated as albumin/total protein-albumin at diagnosis, were compared between both groups. A univariate and multivariate analysis was carried out.

RESULTS

124 (20.8%) patients had LN during follow-up and 471 (79.2%) did not develop LN. Univariate analysis: variables significantly associated with the development of LN: smoking, oral ulcers, serositis, more than four classification criteria, abrupt onset of SLE, higher SLEDAI value, low AGR, low C3 levels, high anti-titers. -Double stranded DNA (anti-dc DNA), anti-nucleosomes and positivity of immunofluorescence in skin. Multivariate analysis: predictors of developing LN: elevated serum levels of anti-dc DNA (odds ratio (OR): 15.82; confidence interval (CI): 1.08-1.22, P < .0001), decrease in the C3 fraction (OR: 36.50; CI: 13.52-81.91, P < .0001) and the RAG < 1 (OR: 47.58; CI: 11.85-79.17, P < .0001).

CONCLUSION

The AGR below one was the greatest predictor of the appearance of LN, together with the low levels of C3 and high levels of anti-dc DNA antibodies, they may contribute to identifying patients with a higher risk of presenting LN.

Intertwined pathways of complement activation command the pathogenesis of lupus nephritis

The complement system is involved in the origin of autoimmunity and systemic lupus erythematosus. Both genetic deficiency of complement components and excessive activation are involved in primary and secondary renal diseases, including lupus nephritis. Among the pathways, the classical pathway has long been accepted as the main pathway of complement activation in systemic lupus erythematosus. However, more recent studies have shown the contribution of factors B and D which implies the involvement of the alternative pathway. While there is evidence on the role of the lectin pathway in systemic lupus erythematosus, it is yet to be demonstrated whether this pathway is protective or harmful in lupus nephritis. Complement is being explored for the development of disease biomarkers and therapeutic targeting. In the current review we discuss the involvement of complement in lupus nephritis.

The role of anticomplement therapy in lupus nephritis

The complement system plays crucial roles in homeostasis and host defense against microbes. Deficiency of early complement cascade components has been associated with increased susceptibility to systemic lupus erythematosus (SLE), whereas excessive complement consumption is a hallmark of this disease. Although enhanced classical pathway activation by immune complexes was initially thought to be the main contributor to lupus nephritis (LN) pathogenesis, an increasing body of evidence has suggested the alternative and the lectin pathways are also involved. Therapeutic agents targeting complement activation have been used in LN patients and clinical trials are ongoing. We review the mechanisms by which complement system dysregulation contributes to renal injury in SLE and summarize the latest evidence on the use of anticomplement agents to manage this condition.

Ex Vivo Test for Measuring Complement Attack on Endothelial Cells: From Research to Bedside

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Lupus Nephritis with Obvious IgA deposits in the Kidneys

OBJECTIVE

The purpose of the current study was to describe the clinico-pathological characteristics and outcomes in patients with lupus nephritis with IgA deposits in the kidneys.

MATERIALS AND METHODS

A total of 258 patients with lupus nephritis with complete clinical data and follow-up was enrolled. They were divided into two groups: the IgA deposits group and the non-IgA deposits group. Their clinico-pathological features and outcomes between the two groups were further compared.

RESULTS

Patients with IgA deposits had significantly lower prevalence of acute kidney failure, higher eGFR, lower plasma levels of C3a, and lower renal pathological chronicity indices scores than those with non-IgA deposits (19.4% vs. 31.8%, 80.9±35.6 vs. 69.1±39.6 ml/min/1.73m², 1045.48 [559.41, 1796.34] vs. 1920.77 [1155.08, 2986.96]ng/ml, and 2 [1, 3] vs. 2.5 [2, 4], respectively, all P<0.05). Patients with IgA deposits also had a higher frequency of the CFH rs6677604-AA/GA genotype in comparison with those with non-IgA deposits (12.0% vs. 8.2%, P=0.469). Using the multivariable Cox hazard analysis, the IgA deposits were identified as a protective factor of survival from the composite events (HR 0.423; 95% CI, 0.219 to 0.816; P=0.01).

CONCLUSIONS

Patients with IgA deposits presented with milder renal damage and a good prognosis, which suggested its protective role in lupus nephritis.

The complex role of adipokines in obesity, inflammation, and autoimmunity

The global obesity epidemic is a major contributor to chronic disease and disability in the world today. Since the discovery of leptin in 1994, a multitude of studies have characterized the pathological changes that occur within adipose tissue in the obese state. One significant change is the dysregulation of adipokine production. Adipokines are an indispensable link between metabolism and optimal immune system function; however, their dysregulation in obesity contributes to chronic low-grade inflammation and disease pathology. Herein, I will highlight current knowledge on adipokine structure and physiological function, and focus on the known roles of these factors in the modulation of the immune response. I will also discuss adipokines in rheumatic and autoimmune diseases.

Expanding the Role of Complement Therapies: The Case for Lupus Nephritis

The complement system is an innate immune surveillance network that provides defense against microorganisms and clearance of immune complexes and cellular debris and bridges innate and adaptive immunity. In the context of autoimmune disease, activation and dysregulation of complement can lead to uncontrolled inflammation and organ damage, especially to the kidney. Systemic lupus erythematosus (SLE) is characterized by loss of tolerance, autoantibody production, and immune complex deposition in tissues including the kidney, with inflammatory consequences. Effective clearance of immune complexes and cellular waste by early complement components protects against the development of lupus nephritis, while uncontrolled activation of complement, especially the alternative pathway, promotes kidney damage in SLE. Therefore, complement plays a dual role in the pathogenesis of lupus nephritis. Improved understanding of the contribution of the various complement pathways to the development of kidney disease in SLE has created an opportunity to target the complement system with novel therapies to improve outcomes in lupus nephritis. In this review, we explore the interactions between complement and the kidney in SLE and their implications for the treatment of lupus nephritis.

Alternative complement pathway activation in thrombotic microangiopathy associated with lupus nephritis

INTRODUCTION/OBJECTIVE

Thrombotic microangiopathy (TMA) in systemic lupus erythematosus is a rare manifestation associated with activation of the complement system. This study aimed to compare plasma and urine complement activation products between patients with active lupus nephritis (aLN) and those with acute TMA plus concomitant active LN (aTMA+aLN).

METHODS

Plasma and urine samples were obtained from 20 patients with aTMA+aLN, 20 patients with aLN matched by the histological activity index, 5 patients with chronic TMA, 20 patients with inactive LN, and 10 kidney donors. Complement fragments C3a, C4a, C4d, Ba, C5a, C5bC9, and factor H were determined by ELISA; and kidney C4d deposition was detected by immunohistochemistry. Patients were followed for > 12 months and complement activation products re-measured after treatment in 10 aTMA+aLN patients.

RESULTS

Both aTMA+aLN and aLN groups had increased circulating C3a, Ba, and C5bC9; and decreased circulating C3, C4, C4a, C4d, and factor H. Urinary C3a, C5a, Ba, and C5bC9 were higher in patients with aTMA+aLN than in aLN. After treatment, levels of circulating C3, C4, and factor H increased; while levels of urinary C3a, C5a, Ba, and C5bC9 decreased in patients with aTMA+aLN. These changes were observed at each aTMA episode in two patients studied during repeated TMA episodes. There was no difference in C4d deposition in glomerular capillaries, tubular basement membrane, peritubular capillaries, and arterioles between patients with aLN and those aTMA+aLN.

CONCLUSIONS

Circulating and urine complement activation products suggest that thrombotic microangiopathy associated with LN is mediated through activation of the alternative complement pathway. Key Points • Immune-complex kidney disease in systemic lupus erythematosus (SLE) is associated with activation of the classical, lectin, and alternative complement pathways • Indirect evidence from measurement of circulating and urinary complement pathway activation products suggests that renal acute thrombotic microangiopathy in SLE is mediated by activation of the alternative complement pathway • C4d kidney immunohistochemistry may be positive in both immune complex nephritis and thrombotic microangiopathy. Therefore, it is not a specific marker of renal thrombotic microangiopathy in SLE.

Complement Properdin Determines Disease Activity in MRL/lpr Mice

Background and objects: In systemic lupus erythematosus, circulating immune complexes activate complement and, when trapped in renal capillaries, cause glomerulonephritis. Mouse models have been used in the preclinical assessment of targeting complement activation pathways to manage chronic inflammation in lupus. Properdin is the only known positive regulator of complement activation, but its role in the severity of lupus nephritis has not been studied yet. Materials and Methods: Fully characterized properdin-deficient mice were crossed with lupus prone MRL/lpr mice on C57Bl/6 background. Results: Compared to MRL/lpr properdin wildtype mice, MRL/lpr properdin-deficient mice had significantly lower anti-DNA antibody titres, TNFα and BAFF levels in serum. The qualitative glomerulonephritic score was less severe and there was significantly less serum creatinine in MRL/lpr properdin-deficient mice compared to MRL/lpr properdin wildtype littermate mice. Conclusion: Properdin plays a significant role in the severity of lupus overall and specifically in the extent of glomerulonephritis observed in MRL/lpr mice. Because MRL/lpr properdin-deficient mice had lower levels of anti-DNA antibodies, inflammatory mediators and markers of renal impairment, the study implies that properdin could constitute a novel therapy target in lupus disease.

Circulating anti-C3b IgG in lupus nephritis: A large cohort study

The current study aimed to analyze the clinical significance and bio-functional properties of anti-C3b IgG based on a lupus nephritis cohort. We found that the prevalence of anti-C3b IgG in our cohort was 47.8%. Patients with positive anti-C3b IgG had significantly higher SLEDAI, lower circulating C3 and C4 levels. Anti-C3b IgG levels were positively correlated with C3 or C1q deposition in kidneys and several active pathological lesions. The positivity of anti-C3b IgG was an independent risk factor for the composite endpoints in the subgroup of proliferative lupus nephritis patients. In vitro, the purified IgG fractions from positive patients resulted in increased C3a generation through the alternative pathway, and interfered factor H and CR1 binding to C3b. Our findings indicated that anti-C3b IgG associated with local renal injury and long-term outcomes in lupus nephritis patients, possibly through leading to the complement alternative pathway over-activation.

Activation of the alternative complement pathway predicts renal outcome in patients with lupus nephritis

OBJECTIVES

The aims of this study were to clarify the activation of complement pathways in patients with lupus nephritis (LN), and to elucidate the association between these complement activation types and clinical outcomes.

METHODS

We enrolled 115 patients with biopsy-proven LN from 2003 to 2016 from the lupus cohort at the Busan Paik Hospital and the Jeju National University Hospital in Korea. The patients were divided into two groups based on the patterns of glomerular complements deposits. The presence of C1q, C4 and/or C3 deposits in the glomerulus was considered evidence for the activation of the classical pathway with or without alternative pathway activation (group 1, N = 93), and glomerular C3 deposition without C1q and C4 deposits was considered as a marker for the alternative pathway limited activation (group 2, N = 22). The study end point was progression of kidney disease defined as a ≥50% reduction in estimated glomerular filtration rate from baseline values or advancement to end-stage renal disease.

RESULTS

The mean estimated glomerular filtration rate and median urine protein-to-creatinine ratio of the patients were 85.7 ± 32.4 mL/min/1.73 m² and 3.1 g/g, respectively, at the time of kidney biopsy. Forty-nine patients (43%) had nephrotic range of proteinuria. Compared to group 1 patients, those in group 2 were older, were more likely to be males and were more hypertensive. In addition, plasma C3 and C4 levels were significantly lower in group 1 patients compared to those in group 2. Moreover, anti-dsDNA concentration was significantly higher in group 1 patients compared to those in group 2. The mean follow-up time was 5.4 ± 3.4 years. The rates of response to one-year immunosuppressive treatment were poorer in group 2 patients compared to those in group 1. During the follow-up time, the progression of kidney disease was significantly higher in group 2 than in group 1 patients.

CONCLUSION

This study showed that there was alternative complement pathway limited activation in the renal tissue in a small number of patients with LN, and these patients had worse renal outcomes compared to patients with glomerular classical complement pathway activation with or without alternative pathway activation.

Targeting the Immune Complex-Bound Complement C3d Ligand as a Novel Therapy for Lupus

Humoral autoimmunity is central to the development of systemic lupus erythematosus (SLE). Complement receptor type 2 (CR2)/CD21 plays a key role in the development of high-affinity Abs and long-lasting memory to foreign Ags. When CR2 is bound by its primary C3 activation fragment-derived ligand, designated C3d, it coassociates with CD19 on B cells to amplify BCR signaling. C3d and CR2 also mediate immune complex binding to follicular dendritic cells. As the development of SLE involves subversion of normal B cell tolerance checkpoints, one might expect that CR2 ligation by C3d-bound immune complexes would promote development of SLE. However, prior studies in murine models of SLE using gene-targeted Cr2-/- mice, which lack both CR2 and complement receptor 1 (CR1), have demonstrated contradictory results. As a new approach, we developed a highly specific mouse anti-mouse C3d mAb that blocks its interaction with CR2. With this novel tool, we show that disruption of the critical C3d-CR2 ligand-receptor binding step alone substantially ameliorates autoimmunity and renal disease in the MRL/lpr model of SLE.

Association between antiphospholipid antibodies and factor Bb in lupus nephritis patients with glomerular microthrombosis

BACKGROUND AND PURPOSE

The mechanism of glomerular microthrombosis (GMT) in patients with lupus nephritis (LN) is largely unknown. The aim of this study is to investigate the association between antiphospholipid antibodies (aPLs) and factor Bb in LN patients with GMT.

METHODS

Patients with biopsy-proven LN hospitalized from July 2015 to July 2018 in our hospital were selected for this study. Levels of lupus anticoagulant (LAC), anticardiolipin antibodies (aCLs), anti-β2-glycoprotein I (anti-β2-GPI) antibodies and factor Bb were measured, and other clinical and pathological data were also obtained during the same period before renal biopsy.

RESULTS

A total of 25 LN patients with GMT and 76 LN patients without GMT were included in this study. In LN patients with GMT, the presence of anti-β2GPI and LAC were both significantly higher than in those without GMT (P < .001 and P = .039, respectively). The level of factor Bb was also higher in LN patients with GMT than in those without GMT (P = .021). In the correlation analysis, Bb level was positively correlated with serum creatinine (r = 0.28, P = .014), activity index (r = 0.24, P = .021) GMT (r = 0.65, P < .001) and IgG-anti-β2GPI (r = 0.771, P < .001).

CONCLUSIONS

Our work suggests that aPLs, especially IgG-anti-β2GPI, may play a role in the progress of GMT, and this process might involve alternative complement activation.

Complement Activation in Progression of Chronic Kidney Disease

Chronic kidney disease (CKD) is a public health problem worldwide, with increasing incidence and prevalence. The mechanisms underlying the progression to end-stage renal disease (ESRD) is not fully understood. The complement system was traditionally regarded as an important part of innate immunity required for host protection against infection and for maintaining host hemostasis. However, compelling evidence from both clinical and experimental studies has strongly incriminated complement activation as a pivotal pathogenic mediator of the development of multiple renal diseases and progressive replacement of functioning nephrons by fibrosis. Both anaphylatoxins, i.e., C3a and C5a, and membrane attack complex (MAC) contribute to the damage that occurs during chronic renal progression through various mechanisms including direct proinflammatory and fibrogenic activity, chemotactic effect, activation of the renal renin-angiotensin system, and enhancement of T-cell immunity. Evolving understanding of the mechanisms of complement-mediated renal injury has led to the emergence of complement-targeting therapeutics. A variety of specific antibodies and inhibitors targeting complement components have shown efficacy in reducing disease in animal models. Moreover, building on these advances, targeting complement has gained encouraging success in treating patients with renal diseases such as atypical hemolytic uremic syndrome (aHUS). Nevertheless, it still requires a great deal of effort to develop inhibitors that can be applied to treat more patients effectively in routine clinical practice.

Complement Therapeutics in Autoimmune Disease

Many autoimmune diseases are characterized by generation of autoantibodies that bind to host proteins or deposit within tissues as a component of immune complexes. The autoantibodies can activate the complement system, which can mediate tissue damage and trigger systemic inflammation. Complement inhibitory drugs may, therefore, be beneficial across a large number of different autoimmune diseases. Many new anti-complement drugs that target specific activation mechanisms or downstream activation fragments are in development. Based on the shared pathophysiology of autoimmune diseases, some of these complement inhibitory drugs may provide benefit across multiple different diseases. In some antibody-mediated autoimmune diseases, however, unique features of the autoantibodies, the target antigens, or the affected tissues may make it advantageous to block individual components or pathways of the complement system. This paper reviews the evidence that complement is involved in various autoimmune diseases, as well as the studies that have examined whether or not complement inhibitors are effective for treating these diseases.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Adipokine interactions promote the pathogenesis of systemic lupus erythematosus

BACKGROUND

Adipokines are chemical mediators released from adipose tissue involved in regulation of appetite, insulin sensitivity, immune system and inflammatory responses. Adipokines contributes to low grade inflammatory response in autoimmune disease like Systemic Lupus Erythematosus (SLE) but the pathophysiology is yet not clear. The aim of this study is to understand role of adipokine interactions in SLE disease pathogenesis.

METHODS

Sixty newly diagnosed treatment naïve SLE patients fulfilling the ACR criteria and forty age-sex matched healthy subjects were enrolled in thiscase-control study. Disease activity in SLE patients was evaluated using SELENA-SLEDAI. Array of adipokines, C1q circulating immune complexes (C1q-CIC), anti-C1q, anti-ribososmal P0 (anti-RibP0) and anti-mitochondrial antibodies (AMA) levels were detected by ELISA. Antinuclear antibodies (ANA) and anti-dsDNA autoantibodieswere detected by Indirect Immunofluorescence (IIF), while antigen specificities were detected by Immunoassay blot. Serum levels of C3 and C4 complement factors were assessed by nephlometer.

RESULTS

Statistically significant elevation in progranulin, adipsin and resistin levels was seen among SLE patients when compared to healthy controls (p < 0.0001). Leptin and omentin levels were significantly reduced in SLE patients (p < 0.0001). There was no statistically significant difference in serum adiponectin, chemerin and visfatin levels when these two groups were compared (p > 0.05). Adiponectin, adipsin and resistin levels were elevated in SLE patients with renal manifestations (p < 0.05). Reduced leptin levels were significantly associated with presence of renal manifestations (p < 0.05). Adiponectin levels positively correlated with disease activity (r = 0.294, p = 0.027) whereas negatively correlated with C3 levels (r = -0.439, p = 0.0007). A positive correlation was observed between hypocomplementemia and leptin levels (p < 0.05). Leptin levels were negatively correlated with disease activity, anti-dsDNA, C1q-CIC and anti-C1q levels (p < 0.05). A significant positive correlation was observed between progranulin levels and anti-ribosomal P0 antibodies (r = 0.499, p < 0.0001).

CONCLUSION

Adipokines levels and associated clinical manifestations suggest involvement of adipokines in disease pathogenesis of SLE. SLE disease activity and complement components may suggest regulatory effect of adipokines (adiponectin and leptin) on disease pathogenesis. Further studies on adipokines in SLE patients with renal manifestations may propose them as prognostic markers in renal damage.

TRIAL REGISTRATION

NA.

Complement Factor D protects mice from ethanol-induced inflammation and liver injury

Complement plays a crucial role in microbial defense and clearance of apoptotic cells. Emerging evidence suggests complement is an important contributor to alcoholic liver disease. While complement component 1, Q subcomponent (C1q)-dependent complement activation contributes to ethanol-induced liver injury, the role of the alternative pathway in ethanol-induced injury is unknown. Activation of complement via the classical and alternative pathways was detected in alcoholic hepatitis patients. Female C57BL/6J [wild type (WT)], C1q-deficient ( C1qa-/-, lacking classical pathway activation), complement protein 4-deficient ( C4-/-, lacking classical and lectin pathway activation), complement factor D-deficient ( FD-/-, lacking alternative pathway activation), and C1qa/FD-/- (lacking classical and alternative pathway activation) mice were fed an ethanol-containing liquid diet or pair-fed control diet for 4 or 25 days. Following chronic ethanol exposure, liver injury, steatosis, and proinflammatory cytokine expression were increased in WT but not C1qa-/-, C4-/-, or C1qa/FD-/- mice. In contrast, liver injury, steatosis, and proinflammatory mediators were robustly increased in ethanol-fed FD-/- mice compared with WT mice. Complement activation, assessed by hepatic accumulation of C1q and complement protein 3 (C3) cleavage products (C3b/iC3b/C3c), was evident in livers of WT mice in response to both short-term and chronic ethanol. While C1q accumulated in ethanol-fed FD-/- mice (short term and chronic), C3 cleavage products were detected after short-term but not chronic ethanol. Consistent with impaired complement activation, chronic ethanol induced the accumulation of apoptotic cells and fibrogenic responses in the liver of FD-/- mice. These data highlight the protective role of complement factor D (FD) and suggest that FD-dependent amplification of complement is an adaptive response that promotes hepatic healing and recovery in response to chronic ethanol. NEW & NOTEWORTHY Complement, a component of the innate immune system, is an important pathophysiological contributor to ethanol-induced liver injury. We have identified a novel role for factor D, a component of the alternative pathway, in protecting the liver from ethanol-induced inflammation, accumulation of apoptotic hepatocytes, and profibrotic responses. These data indicate a dual role of complement with regard to inflammatory and protective responses and suggest that accumulation of apoptotic cells impairs hepatic healing/recovery during alcoholic liver disease.

Essential Roles for Mannose-Binding Lectin-Associated Serine Protease-1/3 in the Development of Lupus-Like Glomerulonephritis in MRL/lpr Mice

The complement system, composed of the three activation pathways, has both protective and pathogenic roles in the development of systemic lupus erythematosus (or lupus), a prototypic autoimmune disease. The classical pathway contributes to the clearance of immune complexes (ICs) and apoptotic cells, whereas the alternative pathway (AP) exacerbates renal inflammation. The role of the lectin pathway (LP) in lupus has remained largely unknown. Mannose-binding lectin (MBL)-associated serine proteases (MASPs), which are associated with humoral pattern recognition molecules (MBL or ficolins), are the enzymatic constituents of the LP and AP. MASP-1 encoded by the Masp1 gene significantly contributes to the activation of the LP. After the binding of MBL/ficolins to pathogens or self-altered cells, MASP-1 autoactivates first, then activates MASP-2, and both participate in the formation of the LP C3 convertase C4b2a, whereas, MASP-3, the splice variant of the Masp1 gene, is required for the activation of the zymogen of factor D (FD), and finally participates in the formation of the AP C3 convertase C3bBb. To investigate the roles of MASP-1 and MASP-3 in lupus, we generated Masp1 gene knockout lupus-prone MRL/lpr mice (Masp1/3^−/− MRL/lpr mice), lacking both MASP-1 and MASP-3, and analyzed their renal disease. As expected, sera from Masp1/3^−/− MRL/lpr mice had no or markedly reduced activation of the LP and AP with zymogen forms of complement FD. Compared to their wild-type littermates, the Masp1/3^−/− MRL/lpr mice had maintained serum C3 levels, little-to-no albuminuria, as well as significantly reduced glomerular C3 deposition levels and glomerular pathological score. On the other hand, there were no significant differences in the levels of serum anti-dsDNA antibody, circulating ICs, glomerular IgG and MBL/ficolins deposition, renal interstitial pathological score, urea nitrogen, and mortality between the wild-type and Masp1/3^−/− MRL/lpr mice. Our data indicate that MASP-1/3 plays essential roles in the development of lupus-like glomerulonephritis in MRL/lpr mice, most likely via activation of the LP and/or AP.

Complement Alternative Pathway׳s Activation in Patients With Lupus Nephritis

OBJECTIVE

The aim of this study was to detect the spectrum of complement activation pathways in circulation and to assess their correlations with clinical and pathologic features in a large lupus nephritis cohort from China.

MATERIALS AND METHODS

Plasma levels of C1q, mannose-binding lectin, C4d, Bb, C3, C3a, C5a and soluble C5b-9 were detected by enzyme-linked immunosorbent assay in 222 patients with active biopsy-proven lupus nephritis, 34 patients with lupus nephritis at remission, 82 patients with active systemic lupus erythematosus without renal involvement and 39 normal controls. The correlations between levels of complement components and clinicopathological features of these patients were further analyzed.

RESULTS

Plasma levels of C1q and C3 significantly decreased, and the levels of Bb, C3a, C5a and soluble C5b-9 were significantly elevated in patients with active lupus nephritis compared with those in remission, active systemic lupus erythematosus without renal involvement group and normal controls. In the lupus nephritis group, soluble C5b-9 levels were inversely correlated with C1q and C4d levels (r = -0.412, P < 0.001 and r = -0.221, P = 0.002, respectively), but more strongly correlated with the level of Bb (r = 0.546, P < 0.001). C3b, Bb and C5b-9 could colocalize on glomeruli in lupus nephritis. Plasma Bb level was significantly correlated with some renal disease activity indices and was a risk factor for renal outcomes (hazard ratio = 1.745; 95% CI: 1.106-2.754; P = 0.017) in the lupus nephritis group.

CONCLUSIONS

Our findings suggested that the activation of the complement alternative pathway might play a more important role in the pathogenesis of lupus nephritis, and factor Bb might be a useful marker for evaluating renal disease activity and outcomes.

Complement in Lupus Nephritis: New Perspectives

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disorder caused by loss of tolerance to self-antigens, the production of autoantibodies and deposition of complement-fixing immune complexes (ICs) in injured tissues. SLE is characterized by a wide range of clinical manifestations and targeted organs, with lupus nephritis being one of the most serious complications. The complement system consists of three pathways and is tightly controlled by a set of regulatory proteins to prevent injudicious complement activation on host tissue. The involvement of the complement system in the pathogenesis of SLE is well accepted; yet, its exact role is still not clear.

SUMMARY

Complement plays dual roles in the pathogenesis of SLE. On the one hand, the complement system appears to have protective features in that hereditary homozygous deficiencies of classical pathway components, such as C1q and C4, are associated with an increased risk for SLE. On the other hand, IC-mediated activation of complement in affected tissues is clearly evident in both experimental and human SLE along with pathological features that are logical consequences of complement activation. Studies in genetically altered mice have shown that lack of complement inhibitors, such as complement factor H (CFH) or decay-accelerating factor (DAF) accelerates the development of experimental lupus nephritis, while treatment with recombinant protein inhibitors, such as Crry-Ig, CR2-Crry, CR2-DAF and CR2-CFH, ameliorates the disease development. Complement-targeted drugs, including soluble complement receptor 1 (TP10), C1 esterase inhibitor and a monoclonal anti-C5 antibody (eculizumab), have been shown to inhibit complement safely, and are now being investigated in a variety of clinical conditions.

KEY MESSAGES

SLE is an autoimmune disorder which targets multiple systems. Complement is centrally involved and plays dual roles in the pathogenesis of SLE. Studies from experimental lupus models and clinical trials support the use of complement-targeted therapy in the treatment of SLE.

The alternative pathway of complement activation may be involved in the renal damage of human anti-glomerular basement membrane disease

Linear deposition of IgG and complement 3 (C3) along glomerular basement membrane (GBM) is generally revealed in the kidneys of human anti-GBM disease. Our recent studies demonstrated the pathogenic role of complement activation in renal damage of this disease. However, the pathways of complement activation were still paradoxical. In this study, renal biopsy tissues from 10 patients with anti-GBM disease were used to investigate the pathways of complement activation by detecting the deposition of various complement components, including C1q, factor B, factor P (properdin), mannose-binding lectin (MBL), C3d, C4d and C5b-9, using immunohistochemistry and immunofluorescence. We found that C1q, factor B, properdin, C3d, C4d and C5b-9 were detected in all the glomeruli of our patients, along GBM with a linear and/or granular staining pattern. Furthermore, C1q, factor B and properdin co-localized well with C5b-9. The properdin also co-localized well with C3d. However, the deposition of MBL was diffusive in mesangium, GBM, Bowman's capsule and within crescents and was not co-localized with C5b-9 but partially co-localized with C4d. The intensity of factor B deposition (3.3 vs. 1.2, P<0.001) and C5b-9 deposition (3.2 vs. 1.6, P<0.001) was significantly stronger in the glomeruli with crescent formation, compared with the glomeruli without crescents. The complement system is overall activated via both the alternative pathway and classical pathway in the kidneys of human anti-GBM disease. The alternative pathway might play an important role in complement activation induced renal damage.

Complement and its receptors: new insights into human disease

Although new activation and regulatory mechanisms are still being identified, the basic architecture of the complement system has been known for decades. Two major roles of complement are to control certain bacterial infections and to promote clearance of apoptotic cells. In addition, although inappropriate complement activation has long been proposed to cause tissue damage in human inflammatory and autoimmune diseases, whether this is indeed true has been uncertain. However, recent studies in humans, especially those using newly available biological therapeutics, have now clearly demonstrated the pathophysiologic importance of the complement system in several rare diseases. Beyond these conditions, recent genetic studies have strongly supported an injurious role for complement in a wide array of human inflammatory, degenerative, and autoimmune diseases. This review includes an overview of complement activation, regulatory, and effector mechanisms. It then focuses on new understandings gained from genetic studies, ex vivo analyses, therapeutic trials, and animal models as well as on new research opportunities.

Lupus nephritis: the evolving role of novel therapeutics

Immune complex accumulation in the kidney is the hallmark of lupus nephritis and triggers a series of events that result in kidney inflammation and injury. Cytotoxic agents and corticosteroids are standard of care for lupus nephritis treatment, but are associated with considerable morbidity and suboptimal outcomes. Recently, there has been interest in using novel biologic agents and small molecules to treat lupus nephritis. These therapies can be broadly categorized as anti-inflammatory (laquinamod, anti-tumor necrosis factor-like weak inducer of apotosis, anti-C5, and retinoids), antiautoimmunity (anti-CD20, anti-interferon α, and costimulatory blockers), or both (anti-interleukin 6 and proteasome inhibitors). Recent lupus nephritis clinical trials applied biologics or small molecules of any category to induction treatment, seeking short-term end points of complete renal response. These trials in general have not succeeded. When lupus nephritis comes to clinical attention during the inflammatory stage of the disease, the autoimmune stage leading to kidney inflammation will have been active for some time. The optimal approach for using novel therapies may be to initially target kidney inflammation to preserve renal parenchyma, followed by suppression of autoimmunity. In this review, we discuss novel lupus nephritis therapies and how they fit into a combinatorial treatment strategy based on the pathogenic stage.

Linking complement and anti-dsDNA antibodies in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus is a severe autoimmune disease that affects multiple organ systems resulting in diverse symptoms and outcomes. It is characterized by antibody production to a variety of self-antigens, but it is specifically associated with those against anti-dsDNA. Anti-dsDNA antibodies are present before the onset of clinical disease and are associated with severe manifestations of lupus such as glomerulonephritis. Their levels fluctuate with changes in disease activity and, in combination with the levels of complement proteins C3 and C4, are strong indicators of disease flare and treatment response in patients with lupus. The decreased complement levels that are noted during flares of lupus activity are believed to be secondary to increased autoantibody production and immune complex formation that results in tissue damage; however, recent data suggest that complement activation can also drive development of these pathogenic autoantibodies. This review will explore the various roles of complement in the development and pathogenesis of anti-dsDNA antibodies.

Absence of CD59 exacerbates systemic autoimmunity in MRL/lpr mice

CD59 is a GPI-anchored membrane regulator of complement expressed on blood cells as well as peripheral tissues. It protects host cells from complement injury by inhibiting formation of the membrane attack complex. Recent studies in mice have suggested also a role of CD59 in T cell immune response that was mechanistically independent of complement. In the present study, we investigated the function of CD59 in the MRL/lpr model of murine lupus. We backcrossed the Cd59a knockout (Cd59a(-/-)) mouse onto the MRL/lpr background and compared Cd59a(+/+)-MRL/lpr and Cd59a(-/-)-MRL/lpr littermates for the development of systemic autoimmunity. We found that CD59a deficiency significantly exacerbated the skin disease and lymphoproliferation characteristic of MRL/lpr mice. It also increased autoantibody titers and caused a higher level of proteinuria in male MRL/lpr mice. Bone marrow transfer experiments indicated that CD59a expression on both bone marrow-derived cells and peripheral tissues played a role in lymphoproliferation, whereas the skin disease phenotype is determined mainly by local CD59a expression. Importantly, C3 gene deletion or C5 neutralization with a blocking mAb in Cd59a(-/-)-MRL/lpr mice did not rescue the proautoimmune phenotype associated with CD59a deficiency. These results together suggest that CD59a inhibits systemic autoimmunity in MRL/lpr mice through a complement-independent mechanism.

Complement alternative pathway activation in the autologous phase of nephrotoxic serum nephritis

The complement cascade is an important part of the innate immune system, but pathological activation of this system causes tissue injury in several autoimmune and inflammatory diseases, including immune complex glomerulonephritis. We examined whether mice with targeted deletion of the gene for factor B (fB(-/-) mice) and selective deficiency in the alternative pathway of complement are protected from injury in the nephrotoxic serum (NTS) nephritis model of antibody-mediated glomerulonephritis. When the acute affects of the anti-glomerular basement membrane antibody were assessed, fB(-/-) mice developed a degree of injury similar to wild-type controls. If the mice were presensitized with sheep IgG or if the mice were followed for 5 mo postinjection, however, the fB(-/-) mice developed milder injury than wild-type mice. The immune response of fB(-/-) mice exposed to sheep IgG was similar to that of wild-type mice, but the fB(-/-) mice had less glomerular C3 deposition and lower levels of albuminuria. These results demonstrate that fB(-/-) mice are not significantly protected from acute heterologous injury in NTS nephritis but are protected from autologous injury in response to a planted glomerular antigen. Thus, although the glomerulus is resistant to antibody-initiated, alternative pathway-mediated injury, inhibition of this complement pathway may be beneficial in chronic immune complex-mediated diseases.

Complement in glomerular disease

The role of the complement system in renal disease has long been recognized, but there have been major advances in our understanding of its role over the past decade. Complement plays a critical role not only in host's defense against infection and preventing damage to "self" tissues but also mediates tissue injury, both in the glomerulus and tubulointerstitium. Although injury may originate in the glomerulus, resulting proteinuria and complement activation within the tubular lumen may lead to tubulointerstitial damage and progressive renal disease. Recent advances in our understanding of the mechanisms by which complement mediates renal injury have led to the development of promising strategies with which complement may be targeted to prevent renal injury and its associated complications.

Regulatory T cell-mediated control of autoantibody-induced inflammation

Autoimmune inflammation including autoantibody-induced inflammation is responsible for the lethal organ damage. Autoantibody-induced inflammation can be separated in two components, autoantibody production, and local inflammatory responses. Accumulating evidence has suggested that regulatory T cells (Treg) control both antibody production and the numbers and functions of effector cells such as innate cells and T helper cells. Autoantibodies are produced by both the follicular and extrafollicular pathways. Recently, follicular regulatory T cells (T(FR)) and Qa-1 restricted CD8(+) Treg were identified as populations that are capable of suppressing follicular T helper cell (T(FH))-mediated antibody production. In local inflammation, CD4(+)CD25(+)Foxp3(+) Treg have the capacity to control inflammation by suppressing cytokine production in T helper cells. Although complement proteins contribute to autoantibody-induced local inflammation by activating innate cells, Treg including CD4(+)CD25(+)Foxp3(+) Treg are able to suppress innate cells, chiefly via IL-10 production. IL-10-secreting T cells such as T regulatory type I (Tr1) and Tr1-like cells might also play roles in the control of Th17 and innate cells. Therefore, several kinds of Tregs have the potential to control autoimmune inflammation by suppressing both autoantibody production and the local inflammatory responses induced by autoantibodies.

Mechanisms of tissue injury in lupus nephritis

Systemic lupus erythematosus is a prototypic autoimmune disease characterized by autoantibody production and immune complex formation/deposition in target organs such as the kidney. Resultant local inflammation then leads to organ damage. Nephritis, a major cause of morbidity and mortality in patients with lupus, occurs in approximately 50% of lupus patients. In the present review, we provide an overview of the current research and knowledge concerning mechanisms of renal injury in both lupus-prone mouse models and human lupus patients.

The dual role of complement in the progression of renal disease in NZB/W F(1) mice and alternative pathway inhibition

Complement plays a dual role in the progression of systemic lupus erythematosus since it has important protective functions, such as the clearance of immune complexes and apoptotic cells, but is also a mediator of renal inflammation. To investigate this balance in a clinically relevant setting, we investigated how targeted inhibition of all complement pathways vs. targeted inhibition of only the alternative pathway impacts immune and therapeutic outcomes in NZB/W F(1) mice. Following onset of proteinuria, mice were injected twice weekly with CR2-fH (inhibits alternative pathway), CR2-Crry (inhibits all pathways at C3 activation step), sCR2 (C3d targeting vehicle) or saline. Sera were analyzed every 2 weeks for anti-dsDNA antibody levels, and urinary albumin excretion was determined. Kidneys were collected for histological evaluation at 32 weeks. Compared to the control group, all CR2-fH, CR2-Crry and sCR2 treated groups showed significantly reduced serum anti-dsDNA antibody levels and strong trends towards reduced glomerular IgG deposition levels. Glomerular C3 deposition levels were also significantly reduced in all three-treated groups. However, significant reductions of disease activity (albuminuria and glomerulonephritis) were only seen in the CR2-fH treated group. These data highlight the dual role played by complement in the pathogenesis of lupus, and demonstrate a benefit of selectively inhibiting the alternative complement pathway, presumably because of protective contributions from the classical and/or lectin pathways. The sCR2 targeting moiety appears to be contributing to therapeutic outcome via modulation of autoimmunity. Furthermore, these results are largely consistent with our previous data using the MRL/lpr lupus model, thus broadening the significance of these findings.

Novel targets for immunotherapy in glomerulonephritis

Glomerulonephritis is a common cause of chronic kidney disease and end stage renal failure. Current therapy relies on variably effective, nonspecific and toxic immunosuppression. Recent insights into underlying biology and disease pathogenesis in human glomerulonephritis combined with advances in the fields of inflammation and autoimmunity promise a cadre of novel targeted interventions. This review highlights the therapeutic potential of two antigens, alpha3 (IV)NC1 collagen and podocyte neutral endopeptidase, and two cell signaling and effector molecules, IgG Fc receptors and complement, judged to be particularly amenable to therapeutic manipulation in man. It is anticipated that continued dissection of pathogenesis in the diverse disorders that comprise the glomerulonephritides will provide the basis for individualized disease-specific therapy.

KRN/I-Ag7 mouse arthritis is independent of complement C3

BACKGROUND

KRN/I-A(g7) (KxB/N) is a mouse model of inflammatory arthritis, which resembles human rheumatoid arthritis. Arthritis in these animals is caused by autoreactivity to a ubiquitously expressed autoantigen, glucose-6 phosphate isomerase. Tolerance is broken at both the T cell and B cell level. The sera from KRN/I-A(g7) mice can induce mouse arthritis in healthy mice. Complement components of the alternative complement pathway, including C3, have been shown to be required in induction of mouse arthritis by serum transfer.

METHODS

We have bred KRN/I-A(g7) mice onto a C3-deficient background and followed cohorts for the spontaneous appearance of arthritis. We have also transferred KxB/N serum to B6.I-A ( g7 ) recipients.

RESULTS

C3-deficient KRN/I-A(g7) mice spontaneously developed severe, destructive arthritis, comparable to that seen in C3-intact KRN/I-A(g7) mice. However, serum transfer experiments confirmed the strong requirement for C3 in the passive model.

CONCLUSION

The pathogenesis of spontaneous KRN/I-A(g7) arthritis can largely proceed by complement-independent pathways and must have pathology effector mechanisms in addition to those seen in the passive serum transfer model.