C5a receptor deficiency attenuates T cell function and renal disease in MRLlpr mice

C5a-C5aR1 axis controls mitochondrial fission to promote podocyte injury in lupus nephritis

Podocytes are essential to maintaining the integrity of the glomerular filtration barrier, but they are frequently affected in lupus nephritis (LN). Here, we show that the significant upregulation of Drp1S616 phosphorylation in podocytes promotes mitochondrial fission, leading to mitochondrial dysfunction and podocyte injury in LN. Inhibition or knockdown of Drp1 promotes mitochondrial fusion and protects podocytes from injury induced by LN serum. In vivo, pharmacological inhibition of Drp1 reduces the phosphorylation of Drp1S616 in podocytes in lupus-prone mice. Podocyte injury is reversed when Drp1 is inhibited, resulting in the alleviation of proteinuria. Mechanistically, complement component C5a (C5a) upregulates the phosphorylation of Drp1S616 and promotes mitochondrial fission in podocytes. Moreover, the expression of C5a receptor 1 (C5aR1) is notably upregulated in podocytes in LN. C5a-C5aR1 axis-controlled phosphorylation of Drp1S616 and mitochondrial fission are substantially suppressed when C5aR1 is knocked down by siRNA. Moreover, lupus-prone mice treated with C5aR inhibitor show reduced phosphorylation of Drp1S616 in podocytes, resulting in significantly less podocyte damage. Together, this study uncovers a novel mechanism by which the C5a-C5aR1 axis promotes podocyte injury by enhancing Drp1-mediated mitochondrial fission, which could have significant implications for the treatment of LN.

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.

Tubular toxicity of proteinuria and the progression of chronic kidney disease

Proteinuria is a well-established biomarker of chronic kidney disease (CKD) and a risk predictor of associated disease outcomes. Proteinuria is also a driver of CKD progression toward end-stage kidney disease. Toxic effects of filtered proteins on proximal tubular epithelial cells enhance tubular atrophy and interstitial fibrosis. The extent of protein toxicity and the underlying molecular mechanisms responsible for tubular injury during proteinuria remain unclear. Nevertheless, albumin elicits its toxic effects when degraded and reabsorbed by proximal tubular epithelial cells. Overall, healthy kidneys excrete over 1000 individual proteins, which may be potentially harmful to proximal tubular epithelial cells when filtered and/or reabsorbed in excess. Proteinuria can cause kidney damage, inflammation and fibrosis by increasing reactive oxygen species, autophagy dysfunction, lysosomal membrane permeabilization, endoplasmic reticulum stress and complement activation. Here we summarize toxic proteins reported in proteinuria and the current understanding of molecular mechanisms of toxicity of proteins on proximal tubular epithelial cells leading to CKD progression.

Identification of potent siRNA targeting complement C5 and its robust activity in pre-clinical models of myasthenia gravis and collagen-induced arthritis

Complement component 5 (C5), an important molecule in the complement cascade, blockade by antibodies shows clinical efficacy in treating complement-mediated disorders. However, insufficient blockading induced by single-nucleotide polymorphisms in the C5 protein or frequent development of "breakthrough" intravascular hemolysis in patients with paroxysmal nocturnal hemoglobinuria treated with eculizumab have been reported. Herein, we developed a lipid nanoparticle (LNP)-formulated siRNA targeting C5 that was efficiently delivered to the liver and silenced C5 expression. We identified a potent C5-siRNA with an in vitro IC₅₀ of 420 pM and in vivo ED₅₀ of 0.017 mg/kg following a single administration. Single or repeated administrations of the LNP-formulated C5-siRNA allowed robust and durable suppression of liver C5 expression in mice. Complement C5 silencing ameliorated C5b-dependent anti-acetylcholine receptor antibody-induced myasthenia gravis and C5a-dependent collagen-induced arthritis symptoms. Similarly, in nonhuman primates, a single administration of C5-siRNA/LNP-induced dose-dependent plasma C5 suppression and concomitantly inhibited serum complement activity; complement activity recovered to the pre-treatment levels at 65 days post administration, thus indicating that the complement activity can be controlled for a specific period. Our findings provide the foundation for further developing C5-siRNA delivered via LNPs as a potential therapeutic for complement-mediated diseases.

The lectin pathway does not contribute to glomerular injury in the nephrotoxic nephritis model

AIMS

Rapidly progressive crescentic glomerulonephritis occurs in number systemic and primary glomerular diseases, including anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody vasculitis and lupus nephritis. Our understanding of pathogenic mechanisms comes from animal models of disease such as the nephrotoxic nephritis model. The lectin pathway of complement activation has been shown to play a key role in several models of inflammation including renal ischaemia reperfusion. However, the lectin pathway is not required for crescentic glomerulonephritis in the anti-myeloperoxidase model of anti-neutrophil cytoplasmic antibody vasculitis. The aim of the current study was to explore the role of the lectin pathway in the nephrotoxic nephritis model, which is another model of crescentic glomerulonephritis.

METHODS

Nephrotoxic nephritis was induced in wild type and mannan-binding lectin-associated serine protease-2 deficient mice. Diseases were assessed by quantifying glomerular crescents and macrophages, in addition to albuminuria and serum creatinine.

RESULTS

There was no difference between wild type and MASP-2 deficient mice in any of the histological or biochemical parameters of disease assessed. In addition, there was no difference in the humoral immune response to sheep IgG.

CONCLUSION

These data show that the lectin pathway of complement activation is not required for the development of crescentic glomerulonephritis in the nephrotoxic nephritis model, reinforcing previous findings in the anti-myeloperoxidase model.

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.

Protective Role of C3aR (C3a Anaphylatoxin Receptor) Against Atherosclerosis in Atherosclerosis-Prone Mice

OBJECTIVE

Emerging evidence suggests that C3aR (C3a anaphylatoxin receptor) signaling has protective roles in various inflammatory-related diseases. However, its role in atherosclerosis has been unknown. The purpose of the study was to investigate the possible protective role of C3aR in aortic atherosclerosis and explore molecular and cellular mechanisms involved in the protection. Approach and Results: C3ar^-/-/Apoe^-/- mice were generated by cross-breeding of atherosclerosis-prone Apoe^-/- mice and C3ar^-/- mice. C3ar^-/-/Apoe^-/- mice and Apoe^-/- mice (as a control) underwent high-fat diet for 16 weeks were assessed for (1) atherosclerotic plaque burden, (2) aortic tissue inflammation, (3) recruitment of CD11b⁺ leukocytes into atherosclerotic lesions, and (4) systemic inflammatory responses. Compared with Apoe^-/- mice, C3ar^-/-/Apoe^-/- mice developed more severe atherosclerosis. In addition, C3ar^-/-/Apoe^-/- mice have increased local production of proinflammatory mediators (eg, CCL2 [chemokine (C-C motif) ligand 2], TNF [tumor necrosis factor]-α) and infiltration of monocyte/macrophage in aortic tissue, and their lesional macrophages displayed an M1-like phenotype. Local pathological changes were associated with enhanced systemic inflammatory responses (ie, elevated plasma levels of CCL2 and TNF-α, increased circulating inflammatory cells). In vitro analyses using peritoneal macrophages showed that C3a stimulation resulted in upregulation of M2-associated signaling and molecules, but suppression of M1-associated signaling and molecules, supporting the roles of C3a/C3aR axis in mediating anti-inflammatory response and promoting M2 macrophage polarization.

CONCLUSIONS

Our findings demonstrate a protective role for C3aR in the development of atherosclerosis and suggest that C3aR confers the protection through C3a/C3aR axis-mediated negative regulation of proinflammatory responses and modulation of macrophage toward the anti-inflammatory phenotype.

Complement Deficiencies Result in Surrogate Pathways of Complement Activation in Novel Polygenic Lupus-like Models of Kidney Injury

Lupus nephritis (LN) is a major contributor to morbidity and mortality in lupus patients, but the mechanisms of kidney damage remain unclear. In this study, we introduce, to our knowledge, novel models of LN designed to resemble the polygenic nature of human lupus by embodying three key genetic alterations: the Sle1 interval leading to anti-chromatin autoantibodies; Mfge8-/- , leading to defective clearance of apoptotic cells; and either C1q-/- or C3-/- , leading to low complement levels. We report that proliferative glomerulonephritis arose only in the presence of all three abnormalities (i.e., in Sle1.Mfge8 -/- C1q -/- and Sle1.Mfge8 -/- C3 -/- triple-mutant [TM] strains [C1q -/-TM and C3-/- TM, respectively]), with structural kidney changes resembling those in LN patients. Unexpectedly, both TM strains had significant increases in autoantibody titers, Ag spread, and IgG deposition in the kidneys. Despite the early complement component deficiencies, we observed assembly of the pathogenic terminal complement membrane attack complex in both TM strains. In C1q-/- TM mice, colocalization of MASP-2 and C3 in both the glomeruli and tubules indicated that the lectin pathway likely contributed to complement activation and tissue injury in this strain. Interestingly, enhanced thrombin activation in C3-/- TM mice and reduction of kidney injury following attenuation of thrombin generation by argatroban in a serum-transfer nephrotoxic model identified thrombin as a surrogate pathway for complement activation in C3-deficient mice. These novel mouse models of human lupus inform the requirements for nephritis and provide targets for intervention.

Inflammaging and Complement System: A Link Between Acute Kidney Injury and Chronic Graft Damage

The aberrant activation of complement system in several kidney diseases suggests that this pillar of innate immunity has a critical role in the pathophysiology of renal damage of different etiologies. A growing body of experimental evidence indicates that complement activation contributes to the pathogenesis of acute kidney injury (AKI) such as delayed graft function (DGF) in transplant patients. AKI is characterized by the rapid loss of the kidney's excretory function and is a complex syndrome currently lacking a specific medical treatment to arrest or attenuate progression in chronic kidney disease (CKD). Recent evidence suggests that independently from the initial trigger (i.e., sepsis or ischemia/reperfusions injury), an episode of AKI is strongly associated with an increased risk of subsequent CKD. The AKI-to-CKD transition may involve a wide range of mechanisms including scar-forming myofibroblasts generated from different sources, microvascular rarefaction, mitochondrial dysfunction, or cell cycle arrest by the involvement of epigenetic, gene, and protein alterations leading to common final signaling pathways [i.e., transforming growth factor beta (TGF-β), p16 ink4a , Wnt/β-catenin pathway] involved in renal aging. Research in recent years has revealed that several stressors or complications such as rejection after renal transplantation can lead to accelerated renal aging with detrimental effects with the establishment of chronic proinflammatory cellular phenotypes within the kidney. Despite a greater understanding of these mechanisms, the role of complement system in the context of the AKI-to-CKD transition and renal inflammaging is still poorly explored. The purpose of this review is to summarize recent findings describing the role of complement in AKI-to-CKD transition. We will also address how and when complement inhibitors might be used to prevent AKI and CKD progression, therefore improving graft function.

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.

High Concentration of C5a-Induced Mitochondria-Dependent Apoptosis in Murine Kidney Endothelial Cells

Patients with a relapse of idiopathic nephrotic syndrome have significantly increased levels of serum complement component 5a (C5a), and proteinuria has been noted in mice treated with C5a via changes in permeability of kidney endothelial cells (KECs) in established animal models. However, the apoptosis of KECs treated with high concentrations of C5a has also been observed. As mitochondrial damage is known to be important in cell apoptosis, the aim of this study was to examine the association between C5a-induced mouse KEC apoptosis and mitochondrial damage. Mouse KECs were isolated and treated with different concentrations of C5a. Cell viability assays showed that a high-concentration mouse recombinant protein C5a (rmC5a) treatment reduced mouse KEC growth. Cell cycle phase analysis, including apoptosis (sub-G1 phase) showed an increased percentage of the subG1 phase with a high-concentration rmC5a treatment. Cytochrome c and caspase 3/9 activities were significantly induced in the mouse KECs after a high-dose rmC5a (50 ng/mL) treatment, and this was rescued by pretreatment with the C5a receptor (C5aR) inhibitor (W-54011) and N-acetylcysteine (NAC). Reactive oxygen species (ROS) formation was detected in C5a-treated mouse KECs; however, W-54011 or NAC pretreatment inhibited high-dose rmC5a-induced ROS formation and also reduced cytochrome c release, apoptotic cell formation, and apoptotic DNA fragmentation. These factors determined the apoptosis of mouse KECs treated with high-dose C5a through C5aR and subsequently led to apoptosis via ROS regeneration and cytochrome c release. The results showed that high concentrations of C5a induced mouse KEC apoptosis via a C5aR/ROS/mitochondria-dependent pathway. These findings may shed light on the potential mechanism of glomerular sclerosis, a process in idiopathic nephrotic syndrome causing renal function impairment.

The C3a/C3aR axis mediates anti-inflammatory activity and protects against uropathogenic E coli-induced kidney injury in mice

Both the C3a/C3aR and C5a/C5aR1 axes are regarded as important pathways for inducing and regulating inflammatory responses. It is well documented that the C5a/C5aR1 axis is a potent inflammatory mediator in the pathogenesis of many clinic disorders. However, our understanding of the role of the C3a/C3aR axis in renal disorders remains limited. Contrary to the C5a/C5aR axis, we now show that the C3a/C3aR axis has a protective role in uropathogenic Escherichia coli (UPEC)-induced renal injury. C3aR-/- mice were found to develop severe renal pathology compared to wild type mice, a pathology characterized by intense tissue damage and an increased bacterial load within the kidney. This was associated with an overwhelming production of pro-inflammatory mediators and increased neutrophil infiltration in the kidney. Bone marrow chimera experiments found that tissue damage and bacterial load were significantly reduced in C3aR-/- mice that received bone marrow from wild type mice, compared with that in mice re-populated with bone marrow from C3aR-/- mice. This supports a critical role for C3aR on myeloid cells in the pathological process. Pharmacological treatment of mice with a C3aR agonist reduced both the extent of tissue injury and bacterial load. Mechanistic analyses indicated that the C3a/C3aR axis downregulates the lipopolysaccharide-induced pro-inflammatory responses in macrophages and facilitates the phagocytosis of UPEC by phagocytes. Thus, our findings clearly demonstrate a protective role of the C3a/C3aR axis in UPEC-induced renal injury, conferred by the suppression of pro-inflammatory responses and enhanced phagocytosis by macrophages.

Complement After Trauma: Suturing Innate and Adaptive Immunity

The overpowering effect of trauma on the immune system is undisputed. Severe trauma is characterized by systemic cytokine generation, activation and dysregulation of systemic inflammatory response complementopathy and coagulopathy, has been immensely instrumental in understanding the underlying mechanisms of the innate immune system during systemic inflammation. The compartmentalized functions of the innate and adaptive immune systems are being gradually recognized as an overlapping, interactive and dynamic system of responsive elements. Nonetheless the current knowledge of the complement cascade and its interaction with adaptive immune response mediators and cells, including T- and B-cells, is limited. In this review, we discuss what is known about the bridging effects of the complement system on the adaptive immune system and which unexplored areas could be crucial in understanding how the complement and adaptive immune systems interact following trauma.

The critical role of C5a as an initiator of neutrophil-mediated autoimmune inflammation of the joint and skin

The deposition of IgG autoantibodies in peripheral tissues and the subsequent activation of the complement system, which leads to the accumulation of the anaphylatoxin C5a in these tissues, is a common hallmark of diverse autoimmune diseases, including rheumatoid arthritis (RA) and pemphigoid diseases (PDs). C5a is a potent chemoattractant for granulocytes and mice deficient in its precursor C5 or its receptor C5aR1 are resistant to granulocyte recruitment and, consequently, to tissue inflammation in several models of autoimmune diseases. However, the mechanism whereby C5a/C5aR regulates granulocyte recruitment in these diseases has remained elusive. Mechanistic studies over the past five years into the role of C5a/C5aR1 in the K/BxN serum arthritis mouse model have provided novel insights into the mechanisms C5a/C5aR1 engages to initiate granulocyte recruitment into the joint. It is now established that the critical actions of C5a/C5aR1 do not proceed in the joint itself, but on the luminal endothelial surface of the joint vasculature, where C5a/C5aR1 mediate the arrest of neutrophils on the endothelium by activating β₂ integrin. Then, C5a/C5aR1 induces the release of leukotriene B₄ (LTB₄) from the arrested neutrophils. The latter, subsequently, initiates by autocrine/paracrine actions via its receptor BLT1 the egress of neutrophils from the blood vessel lumen into the interstitial. Compelling evidence suggests that this C5a/C5aR1-LTB₄/BLT1 axis driving granulocyte recruitment in arthritis may represent a more generalizable biological principle critically regulating effector cell recruitment in other IgG autoantibody-induced diseases, such as in pemphigoid diseases. Thus, dual inhibition of C5a and LTB₄, as implemented in nature by the lipocalin coversin in the soft-tick Ornithodoros moubata, may constitute a most effective therapeutic principle for the treatment of IgG autoantibody-driven diseases.

C5a receptor 1 promotes autoimmunity, neutrophil dysfunction and injury in experimental anti-myeloperoxidase glomerulonephritis

The prospects for complement-targeted therapy in ANCA-associated vasculitis have been enhanced by a recent clinical trial in which C5a receptor 1 (C5aR1) inhibition safely replaced glucocorticoids in induction treatment. C5aR1 primes neutrophils for activation by anti-neutrophil cytoplasmic antibody (ANCA) and is therefore required in models of glomerulonephritis induced by anti-myeloperoxidase antibody. Although humoral and cellular autoimmunity play essential roles in ANCA-associated vasculitis, a role for C5aR1 in these responses has not been described. Here, we use murine models to dissect the role of C5aR1 in the generation of anti-myeloperoxidase autoimmunity and the effector responses resulting in renal injury. The genetic absence or pharmacological inhibition of C5aR1 results in reduced autoimmunity to myeloperoxidase with an attenuated Th1 response, increased Foxp3⁺ regulatory T cells and reduction in generation of myeloperoxidase-ANCA. These changes are mediated by C5aR1 on dendritic cells, which promotes activation, and thus myeloperoxidase autoimmunity and glomerulonephritis. We also use renal intravital microscopy to determine the effect of C5aR1 inhibition on ANCA induced neutrophil dysfunction. We found that myeloperoxidase-ANCA induce neutrophil retention and reactive oxygen species burst within glomerular capillaries. These pathological behaviors are abrogated by C5aR1 inhibition. Thus, C5aR1 inhibition ameliorates both autoimmunity and intra-renal neutrophil activation in ANCA-associated vasculitis.

Complement anaphylatoxins C3a and C5a: Emerging roles in cancer progression and treatment

Recent insights into the role of complement anaphylatoxins C3a and C5a in cancer provide new opportunities for the development of innovative biomarkers and therapeutic strategies. These two complement activation products can maintain chronic inflammation, promote an immunosuppressive microenvironment, induce angiogenesis, and increase the motility and metastatic potential of cancer cells. Still, the diverse heterogeneity of responses mediated by these peptides poses a challenge both to our understanding of the role played by these molecules in cancer progression and to the development of effective treatments. This review attempts to summarize the evidence surrounding the involvement of anaphylatoxins in the biological contexts associated with tumor progression. We also describe the recent developments that support the inhibition of anaphylatoxins, or their cognate receptors C3aR and C5aR1, as a treatment option for maximizing the clinical efficacy of current immunotherapies that target the PD-1/PD-L1 immune checkpoint.

A monoclonal antibody against CD86 and its protection in a murine lupus nephritis model of chronic graft-versus-host disease

CONTEXT

Lupus nephritis is the most common complication that causes the death of systemic lupus erythematosus patients. CD28/CTLA4 and their ligands CD80 or CD86 costimulatory pathway play a pivotal role in autoimmune disease and organ transplantation.

OBJECTIVES

We generated a monoclonal antibody (clone 1D1) against human CD86 (1D1) that could recognize both human and mouse CD86, and blocked the CD86/CD28 costimulatory pathway with our mAb on a murine lupus nephritis model induced with chronic graft-versus-host disease (cGVHD).

MATERIALS AND METHODS

Experimental lupus nephritis mice were induced with cGVHD, and splenocyte population were analyzed by flow cytometry. Autoantibodies and proteinuria were detected to evaluate the severity of lupus nephritis. The change of histopathology was observed by microscopy, fluorescence microscopy and electron microscopy.

RESULTS

we successfully generated a monoclonal antibody against human CD86(1D1). 1D1 mAb could recognize not only human CD86, but also mouse CD86. 1D1 was applied to the cGVHD-induced experimental lupus nephritis model, and our study found the production of ANA and anti-dsDNA in the 1D1-treated group was lower than those in IgG-treated group after four weeks. The pathological injure of kidney in the 1D1-treated group was lighten than that in IgG-treated group.

DISCUSSION AND CONCLUSIONS

Our data showed that blockade of CD86/CD28 with 1D1 induced a significant remission of proteinuria, production of autoantibodies, immune complex deposition and renal parenchyma lesions in experimental mice. Anti-CD86 Abs might be a potential method for immune therapy in autoimmune diseases and transplantation.

Current and Emerging Therapies for Lupus Nephritis

The introduction of corticosteroids and later, cyclophosphamide dramatically improved survival in patients with proliferative lupus nephritis, and combined administration of these agents became the standard-of-care treatment for this disease. However, treatment failures were still common and the rate of progression to ESRD remained unacceptably high. Additionally, treatment was associated with significant morbidity. Therefore, as patient survival improved, the goals for advancing lupus nephritis treatment shifted to identifying therapies that could improve long-term renal outcomes and minimize treatment-related toxicity. Unfortunately, progress has been slow and the current approaches to the management of lupus nephritis continue to rely on high-dose corticosteroids plus a broad-spectrum immunosuppressive agent. Over the past decade, an improved understanding of lupus nephritis pathogenesis fueled several clinical trials of novel drugs, but none have been found to be superior to the combination of a cytotoxic agent and corticosteroids. Despite these trial failures, efforts to translate mechanistic advances into new treatment approaches continue. In this review, we discuss current therapeutic strategies for lupus nephritis, briefly review recent advances in understanding the pathogenesis of this disease, and describe emerging approaches developed on the basis of these advances that promise to improve upon the standard-of-care lupus nephritis treatments.

Quercitrin ameliorates the development of systemic lupus erythematosus-like disease in a chronic graft-versus-host murine model

Systemic lupus erythematosus (SLE) is a serious disorder of immune regulation characterized by overproduction of autoantibodies, lupus nephritis, CD4+ T cell aberrant activation, and immune complex-mediated inflammation. The chronic graft vs. host disease (cGVHD) mouse model is a well-established model of SLE. Quercitrin is a natural compound found in Tartary buckwheat with a potential anti-inflammatory effect that is used to treat heart and vascular conditions. In our previous study, we determined that quercitrin is an immunosuppressant with beneficial effects in mouse models of immune diseases. We hypothesized that quercitrin could prevent lupus nephritis in the cGVHD mouse model by decreasing the production of autoantibodies and inflammatory cytokines, and reducing immune cell activation. cGVHD was induced by injecting DBA/2 spleen cells into the tail vein of BDF1 mice. The cGVHD mice exhibited significant proteinuria, which is a marker of nephritis. Quercitrin decreased the number of serum antibodies, CD4+ T cell activation, as well as the expression levels of T-bet, GATA-3, and selected cytokines. Moreover, quercitrin treatment decreased the expression of inflammatory genes and cytokines in the kidney, as well as in peritoneal macrophages. In addition, quercitrin inhibited LPS-induced cytokines as well as the phosphorylation of ERK, p38 MAPK, and JNK in Raw264.7 cells. Overall, quercitrin ameliorated the symptoms of lupus nephritis in the cGVHD mouse model, which may be due to the inhibition of CD4 T cell activation and anti-inflammatory effects on macrophages.

Isogarcinol Extracted from Garcinia mangostana L. Ameliorates Systemic Lupus Erythematosus-like Disease in a Murine Model

Isogarcinol is a new immunosuppressant that we extracted from Garcinia mangostana L. In the present study, we elucidate its beneficial effect in chronic graft-versus-host disease (cGVHD) in mice -- a model for systemic lupus erythematosus (SLE) in human. The oral administration of 60 mg/kg isogarcinol significantly reduced proteinuria, corrected the abnormal serum biochemical indicator, and decreased the amount of serum antibodies and lowered the renal histopathology score. In addition, isogarcinol alleviated the abnormal activation of CD4 T cells and decreased the expression of inflammatory genes and cytokines in the kidneys and peritoneal macrophages. The mechanism of action of isogarcinol is associated with downregulation of CD4 T cells and inflammatory effects. Therefore, we believe that isogarcinol may be a potential therapeutic drug candidate for future treatment of SLE.

Inhibition of Rho-associated kinase relieves C5a-induced proteinuria in murine nephrotic syndrome

Childhood nephrotic syndrome is mainly caused by minimal change disease which is named because only subtle ultrastructural alteration could be observed at electron microscopic level in the pathological kidney. Glomerular podocytes are presumed to be the target cells whose protein sieving capability is compromised by a yet unidentified permeability perturbing factor. In a cohort of children with non-hereditary idiopathic nephrotic syndrome, we found the complement fragment C5a was elevated in their sera during active disease. Administration of recombinant C5a induced profound proteinuria and minimal change nephrotic syndrome in mice. Purified glomerular endothelial cells, instead of podocytes, were demonstrated to be responsible for the proteinuric effect elicited by C5a. Further studies depicted a signaling pathway involving Rho/Rho-associated kinase/myosin activation leading to endothelial cell contraction and cell adhesion complex breakdown. Significantly, application of Rho-associated kinase inhibitor, Y27632, prevented the protein leaking effects observed in both C5a-treated purified endothelial cells and mice. Taken together, our study identifies a previously unknown mechanism underlying nephrotic syndrome and provides a new insight toward identifying Rho-associated kinase inhibition as an alternative therapeutic option for nephrotic syndrome.

Abrogation of immune complex glomerulonephritis by native carboxypeptidase and pharmacological antagonism of the C5a receptor

Activation of complement generates C5a which leads to signaling through C5aR1. This is tightly controlled, including by the plasma proteins factor H (FH) and carboxypeptidase N. Here we studied a chronic serum sickness (CSS) model of glomerulonephritis (GN) in which there is an active humoral immune response, formation of glomerular immune complexes (ICs), and resulting glomerular inflammation. The antibody response, glomerular IC deposition, the degree of GN, and consequent renal functional insufficiency in CSS were all worse in FH−/− mice compared to wild-type FH+/+ animals. This was ameliorated in the former by giving a C5aR1 antagonist for the final 3 weeks of the 5-week protocol. In contrast, blocking CP-mediated inactivation of C5a increased these disease measures. Thus, complement regulation by both plasma FH and CP to limit the quantity of active C5a is important in conditions where the humoral immune response is directed to a continuously present foreign antigen. Signaling through C5aR1 enhances the humoral immune response as well as the inflammatory response to ICs that have formed in glomeruli. Both effects are relevant even after disease has begun. Thus, pharmacological targeting of C5a in IC-mediated GN has potential clinical relevance.

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.

High titer anti-basement membrane antibodies in a subset of patients with pediatric systemic lupus erythematosus

BACKGROUND/AIMS

There is a critical need for more noninvasive biomarkers to identify nephritis in patients with systemic lupus erythematosus (SLE). Recent studies in a model mouse and an adult SLE patient cohort suggest that anti-basement membrane antibody levels correlate well with lupus activity and kidney injury. The purpose of this study was to assess the anti-basement membrane reactivity in pediatric SLE (pSLE) patients with or without nephritis.

METHODS

Auto-antibodies to basement membrane antigens were assessed using an anti-matrigel ELISA. Endpoint titers were measured in pSLE patients and healthy children, as well as in autoimmune and non-immune mice, with good reproducing capabilities. Findings were also analyzed with respect to the presence or absence of nephritis, dsDNA antibodies, and other manifestations of pSLE.

RESULTS

MRL/lpr mice developed high-titer anti-matrigel antibodies, whereas C57BL/6 mice did not. In a cohort of 21 pSLE patients and 22 pediatric controls, high-titer anti-matrigel IgG, IgM and IgA antibody levels were specific for pSLE. High-titer anti-matrigel IgG3 levels could distinguish with good sensitivity the 13 pSLE patients with a history of nephritis from the 8 non-renal pSLE patients. High-titer anti-matrigel IgG, IgA, IgM or IgG3 did not correlate with positive anti-double stranded DNA, but defined an overlapping subset of patients.

CONCLUSION

The addition of anti-basement membrane antibody testing to serologic testing in pSLE may help to monitor disease activity or to define important subsets of patients with risks for specific disease manifestations.

Ginsenoside Rh1 Improves the Effect of Dexamethasone on Autoantibodies Production and Lymphoproliferation in MRL/lpr Mice

Ginsenoside Rh1 is able to upregulate glucocorticoid receptor (GR) level, suggesting Rh1 may improve glucocorticoid efficacy in hormone-dependent diseases. Therefore, we investigated whether Rh1 could enhance the effect of dexamethasone (Dex) in the treatment of MRL/lpr mice. MRL/lpr mice were treated with vehicle, Dex, Rh1, or Dex + Rh1 for 4 weeks. Dex significantly reduced the proteinuria and anti-dsDNA and anti-ANA autoantibodies. The levels of proteinuria and anti-dsDNA and anti-ANA autoantibodies were further decreased in Dex + Rh1 group. Dex, Rh1, or Dex + Rh1 did not alter the proportion of CD4+ splenic lymphocytes, whereas the proportion of CD8+ splenic lymphocytes was significantly increased in Dex and Dex + Rh1 groups. Dex + Rh1 significantly decreased the ratio of CD4+/CD8+ splenic lymphocytes compared with control. Con A-induced CD4+ splenic lymphocytes proliferation was increased in Dex-treated mice and was inhibited in Dex + Rh1-treated mice. Th1 cytokine IFN-γ mRNA was suppressed and Th2 cytokine IL-4 mRNA was increased by Dex. The effect of Dex on IFN-γ and IL-4 mRNA was enhanced by Rh1. In conclusion, our data suggest that Rh1 may enhance the effect of Dex in the treatment of MRL/lpr mice through regulating CD4+ T cells activation and Th1/Th2 balance.

N-Acetyl-Seryl-Aspartyl-Lysyl-Proline: mechanisms of renal protection in mouse model of systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disease characterized by the development of auto antibodies against a variety of self-antigens and deposition of immune complexes that lead to inflammation, fibrosis, and end-organ damage. Up to 60% of lupus patients develop nephritis and renal dysfunction leading to kidney failure. N-acetyl-seryl-aspartyl-lysyl-proline, i.e., Ac-SDKP, is a natural tetrapeptide that in hypertension prevents inflammation and fibrosis in heart, kidney, and vasculature. In experimental autoimmune myocarditis, Ac-SDKP prevents cardiac dysfunction by decreasing innate and adaptive immunity. It has also been reported that Ac-SDKP ameliorates lupus nephritis in mice. We hypothesize that Ac-SDKP prevents lupus nephritis in mice by decreasing complement C5-9, proinflammatory cytokines, and immune cell infiltration. Lupus mice treated with Ac-SDKP for 20 wk had significantly lower renal levels of macrophage and T cell infiltration and proinflammatory chemokine/cytokines. In addition, our data demonstrate for the first time that in lupus mouse Ac-SDKP prevented the increase in complement C5-9, RANTES, MCP-5, and ICAM-1 kidney expression and it prevented the decline of glomerular filtration rate. Ac-SDKP-treated lupus mice had a significant improvement in renal function and lower levels of glomerular damage. Ac-SDKP had no effect on the production of autoantibodies. The protective Ac-SDKP effect is most likely achieved by targeting the expression of proinflammatory chemokines/cytokines, ICAM-1, and immune cell infiltration in the kidney, either directly or via C5-9 proinflammatory arm of complement system.

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.

Anaphylatoxins in organ transplantation

C3a and C5a (also called anaphylatoxins) are inflammatory peptides generated during complement activation. They do not only play important roles in innate immunity through the initiation and regulation of inflammatory responses, but also significantly influence adaptive immune responses. Organ transplantation triggers an initial inflammatory response and subsequent to the specific immune response (also called the alloimmune response), both of which contribute to graft rejection. Emerging evidence suggests that anaphylatoxins, particularly C5a, are significantly involved in both inflammatory and alloimmune responses following organ transplantation, thus influencing graft outcome. This review will provide the information on our current understanding of the roles for anaphylatoxins in ischemia-reperfusion injury, graft rejection, and transplant tolerance, and the therapeutic potential of targeting anaphylatoxin receptors in organ transplantation.

Glutamine modulates CD8αα(+) TCRαβ(+) intestinal intraepithelial lymphocyte expression in mice with polymicrobial sepsis

OBJECTIVES

CD8αα(+) T-cell receptor (TCR) αβ(+) intestinal intraepithelial lymphocytes (IELs) were found to have a regulatory function in the mucosal immune system. Glutamine (GLN) is an amino acid with immunomodulatory effects. The aim of this study was to investigate the influences of GLN on the proportion of CD8αα(+) TCRαβ(+) IELs and associated inflammatory mediator gene expression in polymicrobial sepsis.

METHODS

Mice were randomly assigned to a normal (NC) group, a sepsis with saline (SS) group, or a sepsis with GLN (SG) group. The NC group was fed a chow diet. Sepsis was induced by cecal ligation and puncture (CLP). The SS group was administered saline, and the SG group was given 0.75 g GLN/kg body weight via a tail vein after CLP. Mice were sacrificed 12 h after CLP, and CD8αα(+) TCRαβ(+) IELs were isolated for further analysis.

RESULTS

Sepsis resulted in a lower percentage of CD8αα(+) TCRαβ(+) IELs, and higher messenger (m)RNA expression of complement 5a receptor, interleukin (IL)-2 receptor β, IL-15 receptor α, and interferon-γ by CD8αα(+) TCRαβ(+) IELs. These immunomodulatory mediator genes decreased, whereas IL-7 receptor and transforming growth factor-β expressions increased in CD8αα(+) TCRαβ(+) IELs in septic mice with GLN administration. Annexin V⁄7-AAD staining revealed significantly lower apoptotic rates of CD8αα(+) TCRαβ(+) IELs in the SG group.

CONCLUSION

A single dose of GLN administered after the initiation of sepsis increased the percentage of CD8αα(+) TCRαβ(+) IELs, prevented apoptosis of CD8αα(+) TCRαβ(+) IELs, and downregulated CD8αα(+) TCRαβ(+) IEL-expressed inflammatory mediators. These results suggest that GLN influenced the distribution and cytokine secretion of the CD8αα(+) TCRαβ(+) IEL subset, which may ameliorate sepsis-induced inflammatory reactions and thus mitigate the severity of intestinal epithelial injury.

Anti-inflammatory activity of IgG1 mediated by Fc galactosylation and association of FcγRIIB and dectin-1

Complement is an ancient danger-sensing system that contributes to host defense, immune surveillance and homeostasis. C5a and its G protein–coupled receptor mediate many of the proinflammatory properties of complement. Despite the key role of C5a in allergic asthma, autoimmune arthritis, sepsis and cancer, knowledge about its regulation is limited. Here we demonstrate that IgG1 immune complexes (ICs), the inhibitory IgG receptor FcγRIIB and the C-type lectin–like receptor dectin-1 suppress C5a receptor (C5aR) functions. IgG1 ICs promote the association of FcγRIIB with dectin-1, resulting in phosphorylation of Src homology 2 domain–containing inositol phosphatase (SHIP) downstream of FcγRIIB and spleen tyrosine kinase downstream of dectin-1. This pathway blocks C5aR-mediated ERK1/2 phosphorylation, C5a effector functions in vitro and C5a-dependent inflammatory responses in vivo, including peritonitis and skin blisters in experimental epidermolysis bullosa acquisita. Notably, high galactosylation of IgG N-glycans is crucial for this inhibitory property of IgG1 ICs, as it promotes the association between FcγRIIB and dectin-1. Thus, galactosylated IgG1 and FcγRIIB exert anti-inflammatory properties beyond their impact on activating FcγRs.

Decreased expression of complement 3a receptor (C3aR) in human placentas from severe preeclamptic pregnancies

OBJECTIVES

The aim of this study was to determine the expression of the anaphylatoxin receptors complement C3a receptor (C3aR) and C5a receptor (C5aR) in the placentas of pregnancies complicated by severe early onset preeclampsia.

STUDY DESIGN

We recruited women with pregnancies complicated by severe early-onset preeclampsia (n=19, 11 of which were further complicated with IUGR) and women with preterm pregnancies not affected by preeclampsia (n=8). Gene and protein expression of C3aR and C5aR was analysed by quantitative RT-PCR and Western blotting, respectively.

RESULTS

C3aR was detected in the Hofbauer cells in the villous stroma of the placenta. C5aR staining was detected in the syncytiotrophoblast and endothelial cells. We found significantly decreased expression of C3aR mRNA and protein expression in placentas with preeclampsia compared to controls. However, C5aR expression was not significantly different between preeclamptic and control placentas at either the mRNA or protein level.

CONCLUSIONS

Decreased C3aR expression indicates a dysregulation of the complement system in the placentas of preeclamptic women. Further studies would elucidate the exact mechanisms that complement has in preeclampsia.

The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice

Chronic serum sickness leads to the formation of glomerular immune complexes; however, C57BL/6 mice do not develop glomerulonephritis unless complement factor H (CFH) is absent from the plasma. Here we studied the role for C5a receptor (R) in this setting. The exaggerated humoral immune response in CFH^−/− mice was normalized in CFH^−/−C5aR^−/− double knockout mice, highlighting the C5aR dependence. The CFH knockout mice developed proliferative glomerulonephritis with endocapillary F4/80⁺ macrophage infiltration, a process reduced in the double knockout mice. There was no interstitial inflammation by histologic criteria or flow cytometry for F4/80⁺Ly6C^hiCCR2^hi inflammatory macrophages. There were, however, more interstitial CD3⁺CD4⁺ T lymphocytes in CFH knockout mice with chronic serum sickness, while double knockout mice had greater than 5-fold more Ly6C^loCCR2^lo anti-inflammatory macrophages compared to the CFH knockout mice. Mice lacking C5aR were significantly protected from functional renal disease as assessed by blood urea nitrogen levels. Thus, IgG- and iC3b-containing immune complexes are not inflammatory in C57BL/6 mice. Yet when these mice lack CFH, sufficient C3b persists in glomeruli to generate C5a and activate C5aR.

C3a and C5a promote renal ischemia-reperfusion injury

Renal ischemia reperfusion injury triggers complement activation, but whether and how the small proinflammatory fragments C3a and C5a contribute to the pathogenesis of this injury remains to be elucidated. Using C3aR-, C5aR-, or C3aR/C5aR-deficient mice and models of renal ischemia-reperfusion injury, we found that deficiency of either or both of these receptors protected mice from injury, but the C3aR/C5aR- and C5aR-deficient mice were most protected. Protection from injury was associated with less cellular infiltration and lower mRNA levels of kidney injury molecule-1, proinflammatory mediators, and adhesion molecules in postischemic kidneys. Furthermore, chimera studies showed that the absence of C3aR and C5aR on renal tubular epithelial cells or circulating leukocytes attenuated renal ischemia-reperfusion injury. In vitro, C3a and C5a stimulation induced inflammatory mediators from both renal tubular epithelial cells and macrophages after hypoxia/reoxygenation. In conclusion, although both C3a and C5a contribute to renal ischemia-reperfusion injury, the pathogenic role of C5a in this injury predominates. These data also suggest that expression of C3aR and C5aR on both renal and circulating leukocytes contributes to the pathogenesis of renal ischemia-reperfusion injury.

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.

Distinct roles for C3a and C5a in complement-induced tubulointerstitial injury

To prevent injury to host tissues, complement activation is regulated by a number of plasma and membrane-associated proteins, most of which limit C3 and C5 activation. An influx of circulating C3 from a syngeneic host into donor kidneys deficient in Crry (a membrane protein that reduces C3 convertase activity) causes spontaneous complement activation, primarily in the tubulointerstitum, leading to renal failure. To determine the roles of the C3a and C5a anaphylatoxins in tubulointerstitial inflammation and fibrosis, kidneys from Crry-/-C3-/- mice were transplanted into hosts lacking the C3a and/or C5a receptor. While unrestricted complement activation in the tubules was not affected by receptor status in the transplant recipient, C3a receptor deficiency in the recipients led to significantly reduced renal leukocyte infiltration and the extent of tubulointerstitial inflammation and fibrosis, all of which led to preserved renal function. The absence of C5a receptors in recipients was not only inconsequential, but the protective effect of C3a receptor deficiency was also eliminated, suggesting distinct roles of C3a and C5a receptor signaling in this model. There was significant infiltration of the tubulointerstitum with 7/4+F4/80+CD11b+ myelomonocytic cells and Thy1.2+ T cells along injured tubules, and interstitial collagen I and III deposition, all of which were C3a receptor dependent. Thus, blockade of C3a receptor signaling is a possible treatment to reduce renal inflammation and preserve renal function associated with complement activation.

Markers of childhood lupus nephritis indicating disease activity

Current treatment regimens for childhood lupus nephritis (LN) are associated with significant side-effects and toxicity in vulnerable phases of growth and development. The paucity of biomarkers particularly in childhood impedes the appropriate clinical management and the development of new therapeutics. We analyzed markers of immune system (BAFF, RANTES), complement (Bb, C1q, C3d-CIC, C5a) and endothelial cell activation (sVCAM-1) in children with LN (n=22, mean age 14.8±4.7 years), nephrotic syndrome (n=13) and age-matched healthy controls (n=20) to define parameters that correlate with LN activity. Complement fragments of the alternative (Bb, p=0.0004) classical (C3d-CIC, p<0.0001) and common pathway (C5a, p<0.0001) and the levels of BAFF (p<0.0001), RANTES (p=0.0002) and sVCAM-1 (p=0.0004) were significantly higher in active compared to inactive LN. Activation of complement was associated with the occurrence of anti-C1q antibodies and reduced complement C1q. Complement-activation fragments highly correlated with the markers for immune system and endothelial cell activation. The ensemble of these parameters may be of great value in identifying early flares or remissions of childhood LN, and moreover may prove useful in the assessment of new treatments and in determining the optimization of their use.

Complement factor H deficiency accelerates development of lupus nephritis

Complement factor H (CfH) is a key regulator of the alternative pathway, and its presence on mouse platelets and podocytes allows the processing of immune complexes. Because of the role of immune complexes in the pathophysiology of lupus nephritis, we studied the role of CfH in the development of nephritis in MRL-lpr mice, an animal model of lupus. At 12 weeks, CfH-deficient MRL-lpr mice had significantly more albuminuria and higher BUN levels than MRL-lpr controls. Cfh-deficient MRL-lpr mice also experienced earlier mortality: at 14 weeks, 6 of 9 CfH-deficient MRL-lpr mice had died of renal failure, whereas all 11 littermate CfH-sufficient MRL-lpr mice were alive (P ≤ 0.001). Histologically, CfH-deficient MRL-lpr mice developed severe diffuse lupus nephritis by 12 weeks (glomerulonephritis scores of 2.6 ± 0.4 versus 0.4 ± 0.2 in littermate controls, P = 0.001). Similar to other CfH-deficient mouse models on nonautoimmune backgrounds, immunofluorescence staining showed extensive linear C3 staining along glomerular capillary walls. IgG was present in the mesangium and peripheral capillary walls along with excessive infiltration of macrophages and neutrophils. Ultrastructurally, there were subendothelial and subepithelial immune deposits and extensive podocyte foot process effacement. In summary, the loss of CfH accelerates the development of lupus nephritis and recapitulates the functional and structural features of the human disease. This illustrates the critical role of complement regulation and metabolism of immune complexes in the pathogenesis of lupus nephritis.

CD3 mAb treatment ameliorated the severity of the cGVHD-induced lupus nephritis in mice by up-regulation of Foxp3+ regulatory T cells in the target tissue: kidney

Teff/Treg imbalance orchestrated the onset and the progression of the lupus nephritis in a DBA/2→B6D2F1 murine model with cGVHD. In this paper, we first used 145-2C11 Ab to treat these human SLE-like diseased animals. The results showed that short-term low-dose anti-CD3 antibody treatment induced a significant remission of established proteinuria, production of autoantibodies, immune complex deposition and renal parenchyma lesions in lupus nephritic mice. Of note, we found a robust up-regulation of Foxp3 mRNA expression in the target tissue: kidney from mice with anti-CD3 antibody treatment compared to those with control IgG treatment. Likewise, an increased renal mRNA abundance for IL-10 was also observed in anti-CD3 antibody treated mice. In contrast, genes associated with inflammation and fibrosis as well as cytokines related to effector T cell responses were down-regulated by anti-CD3 mAb treatment. These findings suggested that short-term low-dose anti-CD3 antibody treatment might induced an IL-10-secreting Foxp3(+) regulatory T cells in this cGVHD target tissue: kidney, that suppressed the activation of effector T cells (Th1, Th2 and Th17), thus ameliorating the severity of the lupus nephritis in mice.

Identification of a new class of small molecule C5a receptor antagonists

C5a is a terminal product of the complement cascade that activates and attracts inflammatory cells including granulocytes, mast cells and macrophages via a specific GPCR, the C5a receptor (C5aR). Inhibition of C5a/C5aR interaction has been shown to be efficacious in several animal models of autoimmune diseases, including RA, SLE and asthma. This account reports the discovery of a new class of C5aR antagonists through high-throughput screening. The lead compounds in this series are selective and block C5a binding, C5a-promoted calcium flux in human neutrophils with nanomolar potency.

Role of the C5a receptor (C5aR) in acute and chronic dextran sulfate-induced models of inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) is a critical public health issue; more and more people are affected, but treatment options remain limited. Complement activation and the anaphylatoxin C5a have been shown to play a role in IBD. In this study, mouse models of acute and chronic dextran sulfate-induced colitis were used to further elucidate the impact of C5a and its receptor (C5aR) on disease development.

METHODS

In C57BL/6J wildtype and C5aR(-/-) mice the extent of complement activation, changes in weight, and water/food consumption were determined. Disease severity was evaluated via a clinical score, histology, cytokine- and myeloperoxidase-determination as well as real-time reverse-transcriptase polymerase chain reaction (RT-PCR) for expression of anaphylatoxin receptors and inflammatory mediators.

RESULTS

C5aR(-/-) mice showed milder disease symptoms, less histological damage, and a lower expression of inflammatory mediators in acute colitis, a setting where complement was activated. In chronic colitis the knockout mice exhibited aggravated weight loss, a higher degree of histological damage and granulocyte infiltration. Intriguingly, increases in C3a-receptor and C5L2 mRNA were dependent on C5aR. Compared to wildtype mice, C5aR(-/-) animals displayed smaller lymph nodes in acute colitis, but extensive swelling and diminished IL-4 and IFN-γ responses in the chronic disease, demonstrating that C5aR modifies T-helper cell polarization.

CONCLUSIONS

C5aR exerts detrimental functions in acute colitis, strongly supporting the idea that a C5aR-antagonist might be useful for IBD treatment. However, since the absence of C5aR was no longer protective and in some regards disadvantageous in chronic IBD, future studies should address the efficacy and the possible side effects of a sustained antagonist treatment.

Urine proteome analysis in murine nephrotoxic serum nephritis

BACKGROUND

Urine contains serum proteins filtered by the glomerulus or secreted by the renal tubules and proteins produced locally by the urinary tract. Proteomic analysis of urine holds the potential as a noninvasive means of studying or monitoring disease activity. In mice, large concentrations of albumin and lipocalins have complicated the ability to identify urinary biomarkers in disease models.

METHODS

Passive nephrotoxic serum nephritis was induced in mice. Urine proteins were identified and quantified by iTRAQ and MALDI-TOF mass spectrometry. Results were compared to Western blotting and multiplex immunoassays.

RESULTS

Large concentrations of major urinary proteins dominate the urine proteome of mice even in the context of acute nephritis. Increased proteinuria caused by nephrotoxic serum nephritis is transient and includes increased albumin excretion. There were no alterations in chemokine excretion. Altered hepcidin excretion was identified, most likely reflecting local production and renal retention.

CONCLUSION

Proteomic analysis of mouse urine remains challenging due to the abundance of a limited subset of proteins. iTRAQ analysis does not circumvent these challenges, but can provide information on post-translational processing of some proteins. Hepcidin is identified as a potential urinary marker of nephritis and its role in disease pathogenesis warrants further study.

C3a receptor deficiency accelerates the onset of renal injury in the MRL/lpr mouse

The development and progression of systemic lupus erythematosus (SLE) is strongly associated with complement activation and deposition. The anaphylatoxin C3a is a product of complement activation with immunomodulatory properties, and the receptor for C3a (C3aR) is not only expressed by granulocytes and antigen presenting cell populations, but it is also strongly up-regulated in lupus prone mice with active nephritis. In order to characterize the role of the C3aR in inflammatory nephritis, we bred C3aR knock out mice onto the MRL/lpr genetic background (C3aR KO MRL). Compared to control MRL/lpr mice, C3aR KO MRL mice had elevated auto-antibody titers and an earlier onset of renal injury. At 8 weeks, renal expression of a wide range of chemokines and chemokine receptors was increased in C3aR KO MRL kidneys compared to controls. Only the expression of MCP-1 was significantly decreased in the C3aR KO MRL mice. The increased chemokine and chemokine receptor expression seen in the C3aR KO MRL mice was associated with a more rapid rise in serum creatinine and the acceleration of renal fibrosis. However, loss of the C3aR had little impact on long-term kidney injury and did not alter survival. These findings suggest that activation of the C3aR plays a protective, not pathologic, role in the early phase of inflammatory nephritis in the MRL/lpr model of SLE.

Increased survival and reduced renal injury in MRL/lpr mice treated with a novel sphingosine-1-phosphate receptor agonist

Agonists of the type 1 sphingosine-1-phosphate (S1P) receptor inhibit lymphocyte migration, causing their sequestration in lymphoid tissue. The S1P agonist FTY720 prolongs the survival of organ allografts and blocks T-cell mediated autoimmune diseases in experimental models; however, it is a non-selective agonist of four of the five S1P receptors. In this study female MRL/lpr mice, which develop an aggressive form of spontaneous autoimmune kidney disease, were treated with a more selective agonist of the type 1 receptor (KRP-203) or vehicle at 12 or 16 weeks of age. Eighty percent of the mice treated at 12 weeks, before the onset of visible disease, survived to the 24 weeks end point with decreased tubulointerstitial disease and significantly fewer infiltrating CD4(+) and CD8(+) T-cells. Only half of the control vehicle-treated mice survived. All of the mice treated at 16 weeks survived with reduced proteinuria. Mice in both groups had significant reductions in circulating lymphocytes. Mice receiving KRP-203 for 8-12 weeks had significant reductions in T-cells and consequently less adenopathy. Ex vivo treatment of lymphocytes from MRL/lpr mice with KRP-203 enhanced their apoptosis. Our study indicates that KRP-203 attenuates kidney injury in MRL/lpr mice, in part, by reducing T-cell infiltrates.

Complement 5a receptor inhibition improves renal allograft survival

Complement activation plays a key role in mediating apoptosis, inflammation, and transplant rejection. In this study, the role of the complement 5a receptor (C5aR) was examined in human renal allografts and in an allogenic mouse model of renal transplant rejection. In human kidney transplants with acute rejection, C5aR expression was increased in renal tissue and in cells infiltrating the tubulointerstitium. Similar findings were observed in mice. When recipient mice were treated once daily with a C5aR antagonist before transplantation, long-term renal allograft survival was markedly improved compared with vehicle-treatment (75 versus 0%), and apoptosis was reduced. Furthermore, treatment with a C5aR antagonist significantly attenuated monocyte/macrophage infiltration, perhaps a result of reduced levels of monocyte chemoattractant protein 1 and the intercellular adhesion molecule 1. In vitro, C5aR antagonism inhibited intercellular adhesion molecule 1 upregulation in primary mouse aortic endothelial cells and reduced adhesion of peripheral blood mononuclear cells. Furthermore, C5aR blockade markedly reduced alloreactive T cell priming. These results demonstrate that C5aR plays an important role in mediating acute kidney allograft rejection, suggesting that pharmaceutical targeting of C5aR may have potential in transplantation medicine.

IFN-gamma and IL-17 production in experimental autoimmune encephalomyelitis depends on local APC-T cell complement production

IFN-gamma- and IL-17-producing T cells autoreactive across myelin components are central to the pathogenesis of multiple sclerosis. Using direct in vivo, adoptive transfer, and in vitro systems, we show in this study that the generation of these effectors in myelin oligodendrocyte glycoprotein(35-55)-induced experimental autoimmune encephalomyelitis depends on interactions of locally produced C3a/C5a with APC and T cell C3aR/C5aR. In the absence of the cell surface C3/C5 convertase inhibitor decay-accelerating factor (DAF), but not the combined absence of DAF and C5aR and/or C3aR on APC and T cells, a heightened local autoimmune response occurs in which myelin destruction is markedly augmented in concert with markedly more IFN-gamma(+) and IL-17(+) T cell generation. The augmented T cell response is due to increased IL-12 and IL-23 elaboration by APCs together with increased T cell expression of the receptors for each cytokine. The results apply to initial generation of the IL-17 phenotype because naive CD62L(high) Daf1(-/-) T cells produce 3-fold more IL-17 in response to TGF-beta and IL-6, whereas CD62L(high) Daf1(-/-)C5aR(-/-)C3aR(-/-) T cells produce 4-fold less.

C5a is not involved in experimental autoimmune myasthenia gravis pathogenesis

C5 deficient mice are highly resistant to experimental autoimmune myasthenia gravis (EAMG) despite intact immune response to acetylcholine receptor (AChR), validating the pivotal role played by membrane attack complex (MAC, C5b-9) in neuromuscular junction destruction. To distinguish the significance of C5a from that of C5b in EAMG pathogenesis, C5a receptor (C5aR) knockout (KO) and wild-type (WT) mice were immunized with AChR to induce pathogenic anti-AChR antibodies. In contrast with C5 deficient mice, C5aR KO mice were equally susceptible to EAMG as WT mice and exhibited comparable antibody and lymphocyte proliferation response to AChR implicating that C5a is not involved in EAMG development.

Locally produced complement fragments C5a and C3a provide both costimulatory and survival signals to naive CD4+ T cells

Costimulatory signals are critical to T cell activation, but how their effects are mediated remains incompletely characterized. Here, we demonstrate that locally produced C5a and C3a anaphylatoxins interacting with their G protein-coupled receptors (GPCRs), C5aR and C3aR, on APCs and T cells both upstream and downstream of CD28 and CD40L signaling are integrally involved in T cell proliferation and differentiation. Disabling these interactions reduced MHC class II and costimulatory-molecule expression and dramatically diminished T cell responses. Importantly, impaired T cell activation by Cd80-/-Cd86-/- and Cd40-/- APCs was reconstituted by added C5a or C3a. C5aR and C3aR mediated their effects via PI-3 kinase-gamma-dependent AKT phosphorylation, providing a link between GPCR signaling, CD28 costimulation, and T cell survival. These local paracrine and autocrine interactions thus operate constitutively in naive T cells to maintain viability, and their amplification by cognate APC partners thus is critical to T cell costimulation.