Activated complement C3: a potentially novel predictor of progressive IgA nephropathy

Heterozygous mutations in factor H aggravate pathological damage in a stable IgA deposition model induced by Lactobacillus casei cell wall extract

Introduction

Activation of complement through the alternative pathway (AP) has a key role in the pathogenesis of IgA nephropathy (IgAN). We previously showed, by intraperitoneal injection of Lactobacillus casei cell wall extract (LCWE), C57BL/6 mice develop mild kidney damage in association with glomerular IgA deposition. To further address complement activity in causing glomerular histological alterations as suggested in the pathogenesis of IgAN, here we used mice with factor H mutation (FHW/R) to render AP overactivation in conjunction with LCWE injection to stimulate intestinal production of IgA.

Methods

Dose response to LCWE were examined between two groups of FHW/R mice. Wild type (FHW/W) mice stimulated with LCWE were used as model control.

Results

The FHW/R mice primed with high dose LCWE showed elevated IgA and IgA-IgG complex levels in serum. In addition to 100% positive rate of IgA and C3, they display elevated biomarkers of kidney dysfunction, coincided with severe pathological lesions, resembling those of IgAN. As compared to wild type controls stimulated by the same high dose LCWE, these FHW/R mice exhibited stronger complement activation in the kidney and in circulation.

Discussion

The new mouse model shares many disease features with IgAN. The severity of glomerular lesions and the decline of kidney functions are further aggravated through complement overactivation. The model may be a useful tool for preclinical evaluation of treatment response to complement-inhibitors.

Targeting complement in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Recent years have witnessed significant improvements in the understanding of the pathogenesis of IgAN and particularly, the pathogenic role of complement activation. The alternative complement pathway is the major complement cascade activator in IgAN, and glomerular C3 deposition has been shown to correlate with disease progression. In addition, several studies have provided insight into the pathogenic role of factor H-related proteins -1 and -5 in IgAN, as independent players in complement dysregulation. The lectin pathway has also been shown to be associated with the severity of IgAN. Glomerular deposition of C4d has been associated with increased histologic disease activity, faster decline in estimated glomerular filtration rate and higher risk of kidney failure. On the other hand, although overlooked in the Oxford classification, numerous studies have shown that the coexistence of thrombotic microangiopathy in IgAN is a significant indicator of a poorer prognosis. All the breakthroughs in the understanding of the contributing role of complement in IgAN have paved the way for the development of new complement-targeted therapies in this disease. Several ongoing trials are evaluating the efficacy of new agents against factor B (iptacopan, Ionis-FB-LRX), C3 (pegcetacoplan), factor D (vemircopan, pelecopan), C5 (ravulizumab, cemdisiran) and C5a receptor 1 (avacopan). In this study, we provide a comprehensive review of the role of complement in IgAN, including the emerging mechanisms of complement activation and the promising potential of complement inhibitors as a viable treatment option for IgAN.

IgA nephropathy

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

Circulating alternative pathway complement cleavage factor Bb is associated with vascular lesions and outcomes in IgA nephropathy

BACKGROUND

Complement alternative pathway (AP) activation is linked to immunoglobulin A nephropathy (IgAN) prognosis severity, but Bb fragment's role is unclear. We examined the relationship between serum Bb fragment concentration at IgAN diagnosis and disease activity and outcomes.

METHODS

This retrospective study included 125 biopsy-proven IgAN patients [age 39.9 years, 75% male, estimated glomerular filtration rate (eGFR) 82 ml/min, proteinuria 0.5 g/day] enrolled from 1984 to 2010 and followed for a minimum of 18 months. Monitoring continued until the last follow-up, end-stage kidney disease (ESKD) or death. Serum Bb fragment was measured using an enzyme-linked immunosorbent assay at diagnosis. Oxford classification and global optical score (GOS) were utilized for pathology assessment.

RESULTS

Patients were followed for a median of 16 years; 42% developed chronic kidney disease stage ≥3, 19% reached ESKD and 9% died. Serum Bb fragment concentration negatively correlated with eGFR values at the last follow-up and positively with vascular and tubular histopathological indices. In univariate Cox regression analyses, higher Bb fragment concentration was associated with ESKD alongside older age, increased body mass index, arterial hypertension, lower eGFR, higher proteinuria, E1, S1, T1-2, GOS and corticotherapy. Patients with Bb levels ≥14.3 μg/ml had shorter mean kidney survival time (19.5 versus 22.7 years, P = .07); after adjusting for progression risk factors, the association persisted [hazard ratio 4.76 (95% confidence interval 1.56-14.43)].

CONCLUSIONS

Serum Bb fragment concentration at diagnosis may predict long-term IgAN outcomes, potentially due to AP activation at the endothelial surface. Further research is needed to confirm these results and evaluate Bb fragment's role in IgAN management.

The role of complement in glomerulonephritis-are novel therapies ready for prime time?

The complement system plays a key pathogenic role in glomerular diseases with a diverse range of aetiologies, including C3 glomerulopathy, immunoglobulin A nephropathy, membranous nephropathy, ANCA-associated vasculitis and lupus nephritis. Several novel therapies targeting complement activity have recently been developed, which have now been approved or are in the late stages of clinical development. In this review, potential benefits and challenges of targeting the complement system in glomerular disease are discussed. We summarize current understanding of the role of complement, and the novel targeted therapies that are being developed for the treatment of glomerular disease.

A bibliometric analysis of complement in IgA nephropathy from 1991 to 2022

Introduction: IgA nephropathy is a common glomerular disease on a global scale, which has resulted in significant economic burdens. The complement system plays a vital role in enhancing the efficacy of antibodies and phagocytic cells in eliminating microbes and damaged cells, and promoting inflammation. Complement activation has been found to contribute to the progression of various renal diseases, including IgA nephropathy. Methods: In this study, a thorough analysis was conducted on publications related to complement in IgAN from 1991 to 2022, retrieved from the Web of Science Core Collection and Scopus database. The analysis focused on various aspects such as annual publications, country, institution, author, journal, keywords, and co-cited references, utilizing Citespace and Vosviewer. Results: A total of 819 publications were obtained, and while there were slight fluctuations in annual publications, an overall upward trend was observed. China, Japan and the United States were the leading countries in terms of publications, with China having the highest number of publications (201). Collaborative network analysis revealed that England, University of Alabama Birmingham, and Robert J Wyatt were the most influential country, institution, and author, respectively, in this field of research. Furthermore, the analysis of references and keywords indicated that complement activation contributes to IgAN, and immunosuppression in IgAN are a hot topic of research. Discussion: This study identifies current research hotspots and advanced tendencies in the study of complement in IgAN, providing scholars with crucial directions in this research area.

Serum and Urine Biomarkers Related to Kidney Fibrosis Predict Kidney Outcome in Czech Patients with IgA Nephropathy

We evaluated biomarkers related to kidney fibrosis for the outcome of patients with IgA nephropathy (IgAN). Clinical parameters (estimated glomerular filtration rate, hypertension, proteinuria) and histological findings were assessed in 134 patients with IgAN at the time of diagnosis and followed up prospectively (mean follow-up time, 56.5 months). We measured biomarkers of collagen and laminin turnover in serum and urine collected at the time of kidney biopsy using a novel enzyme-linked immunosorbent assay. Linear discriminant analysis and logistic regression models were used to predict the patient's kidney outcome. Five serum and urine biomarkers of laminin and collagen turnover (sLG1M, sPRO-C3, sPRO-C6, uPRO-C6/Cr, uC3M/Cr) could significantly differentiae IgAN patients with a worse prognosis. Clinical parameters (glomerular filtration rate (GFR), proteinuria) distinguished patients at risk of IgAN progression with a specificity of 87.3% and a sensitivity of 45.2% (area under the curve-AUC 0.751). The addition of the biomarkers significantly increased the prognostic ability with a specificity of 85.1% and a sensitivity of 73.3% (AUC 0.905). We have identified three serum (sLG1M, sPRO-C3, sPRO-C6) and two urinary markers (uPRO-C6/Cr, u-C3M /Cr) that significantly improve the prognostic ability of markers of kidney function to identify an IgAN patient's risk of progressing to ESKD.

How to take advantage of easily available biomarkers in patients with IgA nephropathy: IgA and C3 in serum and kidney biopsies

IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide. It is diagnosed based on clinical and histological features including predominant IgA deposits in kidney biopsy. The multi-hit theory, based on the production of GDIgA1 and anti-GDIgA1 antibodies, and complement activation via alternative and lectin pathways and also a genetic tendency are crucial in the pathogenesis of IgAN. The aim of the present review is to summarize the utility of routine diagnostic tests in IgA nephropathy, such as IgA and C3 in serum and kidney biopsy specimens, for predicting the disease progression. The paper also contains data on new markers used in the diagnosis and prognosis of IgA nephropathy.

The Contribution of Complement to the Pathogenesis of IgA Nephropathy: Are Complement-Targeted Therapies Moving from Rare Disorders to More Common Diseases?

Primary IgA nephropathy (IgAN) is a leading cause of chronic kidney disease and kidney failure for which there is no disease-specific treatment. However, this could change, since novel therapeutic approaches are currently being assessed in clinical trials, including complement-targeting therapies. An improved understanding of the role of the lectin and the alternative pathway of complement in the pathophysiology of IgAN has led to the development of these treatment strategies. Recently, in a phase 2 trial, treatment with a blocking antibody against mannose-binding protein-associated serine protease 2 (MASP-2, a crucial enzyme of the lectin pathway) was suggested to have a potential benefit for IgAN. Now in a phase 3 study, this MASP-2 inhibitor for the treatment of IgAN could mark the start of a new era of complement therapeutics where common diseases can be treated with these drugs. The clinical development of complement inhibitors requires a better understanding by physicians of the biology of complement, the pathogenic role of complement in IgAN, and complement-targeted therapies. The purpose of this review is to provide an overview of the role of complement in IgAN, including the recent discovery of new mechanisms of complement activation and opportunities for complement inhibitors as the treatment of IgAN.

Is complement the main accomplice in IgA nephropathy? From initial observations to potential complement-targeted therapies

IgA Nephropathy (IgAN) is the main cause of primary glomerulonephritis, globally. This disease is associated with a wide range of clinical presentations, variable prognosis and a spectrum of histological findings. More than fifty years after its first description, this heterogeneity continues to complicate efforts to understand the pathogenesis. Nevertheless, involvement of the complement system in IgAN was identified early on. Dysfunction of the immunoglobulin A (IgA) system, the principal offender in this disease, including modification of isoforms and glycoforms of IgA1, the nature of immune complexes and autoantibodies to galactose deficient IgA1 might all be responsible for complement activation in IgAN. However, the specific mechanisms engaging complement are still under examination. Research in this domain should allow for identification of patients that may benefit from complement-targeted therapy, in the foreseeable future.

Complement activation in IgA nephropathy

IgA nephropathy pathogenesis is incompletely understood, and this limits the development of disease-specific biomarkers and effective therapies. Evidence of complement activity in IgA nephropathy is well established. However, a growing body of research indicates complement activity is an important contributor to IgA nephropathy pathology. In particular, multiple associations have been identified between complement alternative, lectin and terminal pathway proteins and IgA nephropathy severity. Recently, we have also gained insight into possible mechanisms that could link glomerular IgA deposition, complement activity, glomerular inflammation and disease severity. Ongoing clinical trials of therapeutic complement inhibitors will provide insight into the importance of complement activity to IgA nephropathy pathogenesis. Further research into mechanisms of complement activity is essential to improving our understanding and management of patients with IgA nephropathy.

Replacing centrifugation with mixing in urine analysis enriches protein pool in the urine samples

Urine is the basic diagnostic material, easy to collect, not requiring invasive approach. During standard procedure the urine samples are centrifuged and the supernatant analysed physically, biochemically, and microscopically. The centrifugation step removes proteins including those forming aggregates especially in the state of illness and after transplantation. Here, we analysed the effect of urine centrifuging on specific protein content in urine samples obtained from cardiovascular patients (CVD) and after kidney or liver transplantation. We tested homogeneous whole urine samples, standardly centrifuge one, and the pellet after centrifuging. Protein content was examined using Western blot analysis and mass spectrometry (MS) of samples from CVD patients or the one after transplantation. The average of 21% proteins from non-centrifuged samples were found in the pellet removed after standard centrifugation. MS analysis confirmed that diagnostically important proteins were located there in. In 90% of cases whole urine samples contained more proteins than standard supernatant, among them e.g. proteins involved in immunological response like immunoglobulins and complement compounds secreted by leucocytes. Replacing centrifuging with intensive mixing of urine samples provides a method of enriching the samples with proteins removed during standard procedure, thus increasing possibility of finding new biomarkers for diseases undiagnosable with classic urine analysis.

Mesangial C3 deposition and serum C3 levels predict renal outcome in IgA nephropathy

BACKGROUND

Complement activation plays an important role in the pathogenesis of IgA nephropathy (IgAN). We aimed to evaluate the relationship between mesangial C3 deposition and histologic lesions and to investigate the role of mesangial C3 deposition and serum C3 reduction in predicting renal outcome in IgAN children.

METHODS

We performed a retrospective cohort study in children with biopsy-proven IgAN. Mesangial C3 deposition (< 2+ vs. ≥ 2+) was detected by the immunofluorescence. Histopathologic kidney grades were determined by the Oxford classification. A decreased serum C3 concentration (hypoC3) was defined when C3 < 90 mg/dl. The endpoint was composite kidney outcome with either a 30% decline in glomerular filtration rates from baseline or kidney failure during the follow-up period.

RESULTS

A total of 98 children were analyzed. Mesangial hypercellularity (M) was an independent factor associated with mesangial C3 deposition (HR 3.267; 95% CI 1.028-10.389; P = 0.045). After a median follow-up period of 25 months (interquartile range 18-36 months), 6 (6.1%) children reached the endpoint. Compared with other children, a significantly higher proportion of children with composite kidney outcomes had mesangial C3 deposition ≥ 2+ and hypoC3 (3.4% versus 27.3%, P = 0.002). After adjustment for clinicopathologic risk factors, mesangial C3 deposition ≥ 2+ and hypoC3 were associated with renal outcome (HR 9.772; 95% CI 1.264-75.518; P = 0.029).

CONCLUSION

Mesangial C3 deposition was associated with M in IgAN. Mesangial C3 deposition and hypoC3 were risk factors for renal outcome in children with IgAN.

DelCFHR3-1 influences graft survival in transplant patients with IgA nephropathy via complement-mediated cellular senescence

IgA nephropathy (IgAN) is a frequent cause of chronic kidney disease (CKD) and progressive renal impairment. A native renal biopsy diagnosis of IgAN is a predictor of graft loss, with a relative risk of 47% but it is difficult to predict graft survival and progressive allograft dysfunction in these patients. Deletion of complement factor H-related genes 1 and 3 (delCFHR3-1) has been associated with a decreased risk of developing IgAN on native kidneys, but the impact on the graft in IgAN-transplanted patients is unknown. We hypothesized that delCFHR3-1 is also associated with the processes that influence graft survival in transplant recipients with IgAN and tested whether cellular senescence is involved in mediating graft damage. We found that patients carrying two copies of CFHR1-3 had a worse outcome (P = .000321) and presented increased FHR1 deposits at glomerular and tubulointerstitial level associated with higher expression of the senescence marker p16^INK4a (P = .001) and tubulointerstitial fibrosis (P = .005). Interestingly, FHR1 deposits were associated with increased complement activation as demonstrated by C5b-9 deposits. These data support both the role of FHR1 in mediating complement activation and tubular senescence, and suggest the possibility of genotyping delCFHR3-1 to predict graft survival in IgAN-transplanted patients.

The Clinical Significance and Potential Role of Cathepsin S in IgA Nephropathy

Objective: Cathepsin S (CTSS) is an important lysosomal cysteine protease. This study aimed at investigating the clinical significance of CTSS and underlying mechanism in immunoglobulin A nephropathy (IgAN). Methods: This study recruited 25 children with IgAN and age-matched controls and their serum CTSS levels were measured by enzyme-linked immunosorbent assay (ELISA). Following induction of IgAN in rats, their kidney CTSS expression, IgA accumulation and serum CTSS were characterized by immunohistochemistry, immunofluorescence, and ELISA. The impact of IgA1 aggregates on the proliferation of human mesangial cells (HMCs) was determined by Cell Counting Kit-8 and Western blot analysis of Ki67. Results: Compared to the non-IgAN controls, significantly up-regulated CTSS expression was detected in the renal tissues, particularly in the glomerular mesangium and tubular epithelial cells of IgAN patients, accompanied by higher levels of serum CTSS (P < 0.05), which were correlated with the levels of 24-h-urine proteins and microalbumin and urine erythrocytes and grades of IgAN Lee's classification in children with IgAN (P < 0.01 for all). Following induction of IgAN, we detected inducible IgA accumulation and increased levels of CTSS expression in the glomerular mesangium and glomerular damages in rats, which were mitigated by LY3000328, a CTSS-specific inhibitor. Treatment with LY3000328 significantly mitigated the Ki67 expression in the kidney of IgAN rats (P < 0.01) and significantly minimized the IgA1 aggregate-stimulated proliferation of HMCs and their Ki67 expression in vitro (P < 0.01). Conclusions: CTSS promoted the proliferation of glomerular mesangial cells, contributing to the pathogenesis of IgAN and may be a new therapeutic target for intervention of aberrant mesangial cell proliferation during the process of IgAN.

Emerging role of ficolins in autoimmune diseases

Ficolins are pattern-recognition molecules (PRMs) that could form complexes with mannose-binding lectin-associated serine proteases (MASPs) to trigger complement activation via the lectin pathway, thereby mediating a series of immune responses including opsonization, phagocytosis and cytokine production. In the past few decades, accumulating evidence have suggested that ficolins play a major role in the onset and development of several autoimmune diseases (ADs), including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc), Type 1 diabetes (T1D), inflammatory bowel disease (IBD), etc. In this review, we synthesized previous literatures and recent advances to elucidate the immunological regulations of ficolins and discuss the potential diagnostic ability of ficolins in ADs, as well as giving an insight into the future therapeutic options for ficolins in ADs.

Clinical and prognostic significance of C1q deposition in IgAN patients-a retrospective study

BACKGROUND/AIM

IgA nephropathy (IgAN) is the most prevalent primary glomerular disease worldwide and is responsible for 45-50% of primary glomerular diseases in China. We are essentially dependent on the degree of proteinuria to determine prognosis and it has been reported that histopathologic lesions are risk factors for the progression of IgAN. The aim of this study was to investigate the clinicopathologic features and prognosis of IgAN with C1q deposition in adult Chinese patients.

METHODS

The patients of primary IgAN diagnosed by renal biopsy from January 2002 to December 2018 at the Second Hospital of Shanxi Medical University were retrospectively analyzed and divided into C1q deposit group and C1q negative group according to glomerular immunofluorescence examination. We evaluated their serologic and histopathologic findings. We collected data of patients during January 1, 2015 to December 31, 2018 and performed the clinical follow-up until the patient's estimated glomerular filtration rate (eGFR) decreased by more than 30%, entering end-stage renal disease (ESRD). Kaplan-Meier survival analysis was used to evaluate the cumulative incidence of renal progression in two groups. Univariate and multivariate Cox proportional hazard regression models were used to analyze the effect of C1q deposition on the prognosis of patients with IgA nephropathy.

RESULTS

The baseline data of total 491 cases were available and 172 cases had the follow-up data. The baseline eGFR and plasma albumin (ALB) levels in C1q deposit group were lower than those in the C1q negative group, while the levels of serum creatinine (Scr), total cholesterol (TC), 24 h urine protein, low-density lipoprotein (LDL), β2 microglobulin, etc. were higher than those in C1q negative group (all P < 0.05). Pathological indexes: glomerular segment sclerosis and adhesion (S), renal tubular atrophy/interstitial fibrosis (T), and cell/fibroblastic crescent (C) scores in C1q deposit group were higher than those in C1q negative group (all P < 0.05). With a median follow-up time of 32.5 (24,42) months, a total of 18 patients (C1q deposit: 11; C1q negative: 7) developed to endpoints. Kaplan-Meier survival curve analysis showed that there was significant decrease in cumulative incidence of renal progression between the two groups (Log-rank test χ2 = 4.78, P = 0.029). Cox regression analysis showed that the risk of renal end-point events in IgAN patients with C1q deposit group was 6.35 times higher than that in C1q negative group (HR = 6.35, 95% CI: 1.21-33.30, P = 0.029).

CONCLUSION

The clinical and renal pathological changes of IgAN patients with C1q deposition are more severe than those of C1q negative patients, and has a worse outcome. C1q deposition is an independent risk factor for the progression of renal function and contributes to a poor renal prognosis in adult IgAN patients.

Neutrophil-to-lymphocyte ratio as an independent inflammatory indicator of poor prognosis in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is achronic immuno-inflammatory progressive disease. Several systemic inflammatory indicators, mainly the neutrophil-to-lymphocyte ratio (NLR), are regarded as valuable markers for many diseases, such as IgA vasculitis and chronic kidney disease. Here, we investigated multiple peripheral blood indicators in a large IgAN registry with regular follow-up to evaluate their effects on IgAN phenotypes and progression.

METHODS

Totally, 1151 IgAN patients with regular follow-up, and 251 healthy volunteers were enrolled. Complete blood count test results, including counts of white blood cells (WBC), neutrophils (NE), lymphocyte (LY), and platelets (PLT), were collected from medical records. Then, NLR and PLR were calculated.

RESULTS

IgAN patients presented with increased WBC, NE, NLR and PLR levels and decreased LY levels compared with controls. In univariate survival analysis, WBC, NE and NLR showed significant associations with IgAN progression, and NLR had a higher area under the ROC curves than NE and WBC. When adjusted for well-known risk factors, NLR remained an independent risk factor for poor renal outcome in IgAN patients and performed better than NE. By using NLR 2.40 as cutoff point, IgAN patients were divided into two groups. IgAN patients in the high NLR group presented with lower eGFR, higher proteinuria, higher incidence of hypertension, and more severe pathological lesions, as well as lower event-free renal survival rate.

CONCLUSIONS

We found patients with IgAN had elevated NLR levels than healthy controls, and the easily available NLR in clinical practice could serve as an independent risk factor for IgAN progression.

IgA nephropathy in children and in adults: two separate entities or the same disease?

IgA nephropathy (IgAN) is observed in subjects of any age, however perspective and management of this disease are different between adult and pediatrician Nephrologists. Most children with IgAN present with gross hematuria rapidly vanishing or persistent mild microscopic hematuria, which rarely progresses to end stage renal disease (ESRD) over the pediatric observation. The perspective of IgAN in adults is of a slowly progressive glomerular disease with 30-40% probabilities to reach ESRD. However, mild cases of IgAN in children might be missed with manifestation of irreversible damage only decades after the true onset, as 50% of subjects with IgAN enter renal replacement treatment before the age of 50 years. In both adults and children the assessment of risk profile is crucial to avoid overtreatment in benign cases or institute a prompt and valid therapy in potentially progressive cases. In case of common risk factors, new therapeutic opportunities tested in adults might be applied to children with the expectation of similar results. If IgAN is the same disease in spite of different clinical profiles in children and adults, an early intervention may be the correct way to prevent progression decades later. On the contrary, if we are dealing with different clinical entities, the treatment in pediatric and in adult settings must be kept apart. This review addresses to report similarities and differences of IgAN across the life periods in order to reason on the application of newly offered treatments over the entire spectrum of this disease or in focused age indications.

Current Trends on Glomerulosclerosis Regression

The role of the renin-angiotensin system in hypertension and end-organ damage has long been recognized. Angiotensin l converting enzyme inhibitors are superior to other antihypertensive agents in protecting the kidney against progressive deterioration, even in normotensive persons. Likewise, angiotensin II type 1 receptor antagonists improve or even reverse glomerulosclerosis in rat animal models. These findings suggest that Angiotensin II has nonhemodynamic effects in progressive renal disease. The renin-angiotensin system is now recognized to be linked to the induction of plasminogen activator-inhibitor-1, possibly via the AT4 receptor, thus promoting both thrombosis and fibrosis. Interactions of the renin-angiotensin system with aldosterone and bradykinin may impact both blood pressure and tissue injury. The beneficial effect on renal fibrosis of inhibiting the renin-angiotensin system likely reflects the central role that angiotensin has in regulating renal function and structure by its various actions. This article explores the renin-angiotensin-aldosterone system with plasminogen activator-inhibitor-1 interaction and the potential significance of these interactions in the pathogenesis of progressive renal disease and remodeling of renal sclerosis.

The Role of Immune Modulation in Pathogenesis of IgA Nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide, with diverse clinical manifestations characterized by recurrent gross hematuria or microscopic hematuria, and pathological changes featuring poorly O-galactosylated IgA1 deposition in the glomerular mesangium. Pathogenesis has always been the focus of IgAN studies. After 50 years of research, most scholars agree that IgAN is a group of clinicopathological syndromes with certain common immunopathological characteristics, and multiple mechanisms are involved in its pathogenesis, including immunology, genetics, and environmental or nutritional factors. However, the precise pathogenetic mechanisms have not been fully determined. One hypothesis about the pathogenesis of IgAN suggests that immunological factors are engaged in all aspects of IgAN development and play a critical role. A variety of immune cells (e.g., dendritic cells, NK cells, macrophages, T-lymphocyte subsets, and B-lymphocytes, etc.) and molecules (e.g., IgA receptors, Toll-like receptors, complements, etc.) in innate and adaptive immunity are involved in the pathogenesis of IgAN. Moreover, the abnormality of mucosal immune regulation is the core of IgAN immunopathogenesis. The roles of tonsil immunity or intestinal mucosal immunity, which have received more attention in recent years, are supported by mounting evidence. In this review, we will explore the latest research insights on the role of immune modulation in the pathogenesis of IgAN. With a better understanding of immunopathogenesis of IgAN, emerging therapies will soon become realized.

Relationship between serum C3/C4 ratio and prognosis of immunoglobulin A nephropathy based on propensity score matching

Background

Aberrant activation of the complement system plays an important role in the pathogenesis and development of immunoglobulin A nephropathy (IgAN). The relationship between serum complement and the clinical-histopathological features and outcomes of IgAN is controversial. This retrospective study aimed to examine the relationship between the complement 3/4 (C3/C4) ratio and the clinicopathologic changes and prognosis of patients with IgAN.

Methods

A total of 397 patients with primary IgAN from January 2007 to December 2012 at the Chinese People's Liberation Army General Hospital were included in this study. The correlation test and Chi-square test or one-way analysis of variance test were performed to evaluate the relationship between the C3/C4 ratio and other clinical-pathological factors. Propensity score matching and a multivariate Cox regression model were used to calculate the risk factors of renal outcome.

Results

The median follow-up period was 75 months. During the follow-up period, 62 patients (15.6%) developed into the end-stage renal disease (ESRD). The C3/C4 ratio at baseline was associated with the level of serum creatinine (SCr), 24 h urinary protein excretion (24 h Upre), global glomerular sclerosis, and tubulointerstitial lesion. The level of SCr and 24 h Upre and the degree of chronic kidney injury were statistically different among groups defined by different C3/C4 ratio levels. The survival rates of patients among groups with different C3/C4 ratio levels were different. After propensity score matching, eighty-eight pairs of patients were successfully matched, and the C3/C4 ratio was an influencing factor for the patients’ outcome (hazard ratio 0.587, 95% confidence interval 0.329–0.880). Patients with a C3/C4 ratio <3.6 had a poorer outcome compared with the others (P = 0.002).

Conclusions

IgAN patients with decreased C3/C4 ratio displayed significantly more severe clinical symptoms and chronic renal injury than patients with higher ratios. A low C3/C4 ratio could be a risk factor for patients developing to ESRD.

Complement in IgA Nephropathy: The Role of Complement in the Pathogenesis, Diagnosis, and Future Management of IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is an important cause of chronic and end-stage kidney disease. IgAN pathogenesis is incompletely understood. In particular, we cannot adequately explain the heterogeneity in clinical and histologic features and severities that characterizes IgAN. This limits patient stratification to appropriate and effective treatments and the development of disease-targeted therapies. Studies of the role of the alternative, lectin, and terminal complement pathways in IgAN have enhanced our understanding of disease pathogenesis and inform the development of novel diagnostic and therapeutic strategies. For example, recent genetic, serologic, and immunohistologic evidence suggests that imbalances between the main alternative complement pathway regulator protein (factor H) and competitor proteins that deregulate complement activity (factor H-related proteins 1 and 5, FHR1, and FHR5) associate with IgAN severity: a relative abundance of FHR1 and FHR5 amplifies complement-dependent inflammation and exacerbates kidney injury. Ongoing characterization of the mechanisms by which complement activity contributes to IgAN pathogenesis will facilitate the development of complement-based diagnostic techniques, biomarkers of disease activity and severity, and novel targeted therapies.

Defective gene expression of the membrane complement inhibitor CD46 in patients with progressive immunoglobulin A nephropathy

BACKGROUND

Complement is thought to play a role in immunoglobulin A nephropathy (IgAN), though the activating mechanisms are unknown. This study focused on the gene expression of CD46 and CD55, two key molecules for regulating C3 convertase activity of lectin and alternative complement pathways at a cellular level.

METHODS

The transcriptional expression in peripheral white blood cells (WBCs) of CD46 and CD55 was investigated in 157 patients enrolled by the Validation of the Oxford Classification of IgAN group, looking for correlations with clinical and pathology features and estimated glomerular filtration rate (eGFR) modifications from renal biopsy to sampling. Patients had a previous median follow-up of 6.4 (interquartile range 2.8-10.7) years and were divided into progressors and non-progressors according to the median value of their velocity of loss of renal function per year (-0.41 mL/min/1.73 m2/year).

RESULTS

CD46 and CD55 messenger RNA (mRNA) expression in WBCs was not correlated with eGFR values or proteinuria at sampling. CD46 mRNA was significantly correlated with eGFR decline rate as a continuous outcome variable (P = 0.014). A significant difference was found in CD46 gene expression between progressors and non-progressors (P = 0.013). CD46 and CD55 mRNA levels were significantly correlated (P < 0.01), although no difference between progressors and non-progressors was found for CD55 mRNA values. The prediction of progression was increased when CD46 and CD55 mRNA expressions were added to clinical data at renal biopsy (eGFR, proteinuria and mean arterial blood pressure) and Oxford MEST-C (mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, presence of any crescents) score.

CONCLUSIONS

Patients with progressive IgAN showed lower expression of mRNA encoding for the complement inhibitory protein CD46, which may implicate a defective regulation of C3 convertase with uncontrolled complement activation.

Predictive value of mesangial C3 and C4d deposition in IgA nephropathy

We aimed to determine the relative contribution of each complement (C3 and C4d) deposition to the progression of IgA nephropathy (IgAN). We enrolled a total of 380 patients with biopsy-confirmed IgAN. Mesangial deposition of C3(<2+ vs. ≥2+) and C4d(positive vs. negative) was evaluated by immunofluorescence staining and immunohistochemistry, respectively. Study endpoint was the composite of a 30% decline in eGFR or ESRD. The risk of reaching the primary outcome was significantly higher in patients having C3 ≥ 2+ and C4d(+) than in corresponding counterparts. Adding C3 deposition to clinical data acquired at kidney biopsy modestly increased the area under the receiver-operating characteristic curve, net reclassification improvement, and integrated discrimination improvement (IDI); adding C4d increased IDI only. In conclusion, mesangial C3 and C4d deposition was an independent risk factor for progression of IgAN. C3 showed better predictability than C4d, suggesting that lectin pathway alone has limited clinical prognostic value.

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.

The role of complement in IgA nephropathy

IgA nephropathy (IgAN) is common and often progresses to end stage renal disease. IgAN encompasses a wide range of histology and clinical features. IgAN pathogenesis is incompletely understood; the current multi-hit hypothesis of IgAN pathogenesis does not explain the range of glomerular inflammation and renal injury associated with mesangial IgA deposition. Although associations between IgAN and glomerular and circulating markers of complement activation are established, the mechanism of complement activation and contribution to glomerular inflammation and injury are not defined. Recent identification of specific complement pathways and proteins in severe IgAN cases had advanced our understanding of complement in IgAN pathogenesis. In particular, a growing body of evidence implicates the complement factor H related proteins 1 and 5 and lectin pathway as pathogenic in a subset of patients with severe disease. These data suggest complement deregulation and activity may be dominant drivers of renal injury in IgAN. Thereby, markers of complement activation may identify IgAN patients likely to progress to significant renal impairment and complement inhibition may emerge as an effective method of preventing and reducing glomerular injury in IgAN.

IgA nephropathy: new insights into the role of complement

Glomerular complement deposition is common in IgA nephropathy, and recent genome-wide association studies point to a role of complement factor H and complement factor H-related proteins in disease susceptibility. A number of recent studies have now documented elevated levels of some factor H-related proteins in IgA nephropathy, which might contribute to enhanced complement activation.

Biomarkers and Precision Medicine in IgA Nephropathy

The field of biomarker research in IgA nephropathy has experienced a major boost in recent years with the publication of a large number of scientific reports. Candidate biomarkers from blood, urine, and renal tissue obtained through the use of clinical chemistry, molecular biology, and omics have been proposed for translation in clinical practice. Nevertheless, individual biomarkers often lack sensitivity and specificity with the consequent impairment of disease specificity. This review, moving on from the analysis of the four-hit hypothesis, illustrates the biomarkers linked to the abnormal glycosylation process of IgA1 and the immune complex formation. It also describes other serum and urinary biomarkers. Given the profound insights into the pleiotropic function of a single biomarker that is specific for a pathophysiological mechanism, this review suggests a novel approach based on a panel of biomarkers that covers the entire pathogenic process of the disease. Clinical bioinformatics that integrate genetic, clinical, and bioinformatics data sets could optimize the specific value of each biomarker in a multimarker panel. This is a promising approach for precision medicine and personalized therapy in IgA nephropathy.

Treatment of IgA Nephropathy: Evolution Over Half a Century

Fifty years into the original description of IgA nephropathy, there is still no specific therapy for this condition and general measures including blood pressure control with blockers of the renin-angiotensin-aldosterone system and salt restriction remain the cornerstone to slow disease progression. Although the paucity in treatment advances could be related to the disease's complex pathogenesis, which requires multiple hits, heterogeneity as reflected by diverse ethnic differences, and genetic predisposition and histopathologic variations, many nonspecific and immunomodulatory agents have been tested with variable degrees of success and tribulations. Here, we review the evolution of these different therapeutic approaches over time that culminated in the 2012 Kidney Disease: Improving Global Outcomes Clinical Practice Guideline for Glomerulonephritis that presently is being updated, and provide an appraisal of recent data on various forms of immunosuppressive agents. Finally, we discuss the theoretical basis of ongoing and upcoming clinical trials that are more pathway- or cell-type-specific as knowledge in disease mechanisms advances.

Serum C3/C4 ratio is a novel predictor of renal prognosis in patients with IgA nephropathy: a retrospective study

IgA nephropathy (IgAN) is an autoimmune disease associated with complement activation. It is unclear whether the ratio of serum C3 and C4 concentrations (C3/C4 ratio) can predict renal outcomes in IgAN patients. A total of 1503 patients diagnosed with IgAN via renal biopsy were recorded in this study. Poor renal outcomes were defined as > 50% decrease in the baseline estimated glomerular filtration rate (eGFR) or development of end-stage renal disease (ESRD) during follow-up. In total, 712 patients meeting the exclusion/inclusion criteria were selected, and the mean follow-up period was 40.6 (12.34) months. Patients with decreased C3/C4 ratios displayed significantly more severe clinical characteristics and renal pathological features and a higher proportion of poor renal outcomes and ESRD. The optimal multivariate Cox regression models identified the C3/C4 ratio (hazard ratio (HR) 0.63, 95% CI 0.5-0.9), serum uric acid (HR 1.58, 95% CI 1.2-2.2), serum creatinine (HR 1.3, 95% CI 1.1-1.6), systolic blood pressure (HR 1.57, 95% CI 1.2-2.0) and T score (relative to T0, T1: HR 1.96, 95% CI 1.1-3.7, T2: HR 3.03, 95% CI 1.6-5.9) as strong predictors of poor renal outcomes. Subgroup analysis showed that patients with low C3/C4 ratios benefited from glucocorticoids or other immunosuppressive agents (hazard ratio 0.30 and 0.18, 95% CI 0.13-0.72 and 0.07-0.46, respectively). Serum C3/C4 ratios may be an independent novel predictor of renal outcomes in IgAN patients. Decreased C3/C4 ratios suggest poor renal outcomes and the potential to benefit from aggressive immunosuppressive therapies.

The Emerging Role of Complement Proteins as a Target for Therapy of IgA Nephropathy

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide and a common cause of end-stage renal disease. Evaluation of a kidney biopsy is necessary for diagnosis, with routine immunofluorescence microscopy revealing dominant or co-dominant IgA immunodeposits usually with complement C3 and sometimes IgG and/or IgM. IgA nephropathy reduces life expectancy by more than 10 years and leads to kidney failure in 20–40% of patients within 20 years of diagnosis. There is accumulating clinical, genetic, and biochemical evidence that complement plays an important role in the pathogenesis of IgA nephropathy. The presence of C3 differentiates the diagnosis of IgA nephropathy from the subclinical deposition of glomerular IgA. Markers for the activation of the alternative and mannan-binding lectin (MBL) pathways in renal-biopsy specimens are associated with disease activity and portend a worse renal outcome. Complement proteins in the circulation have also been evaluated in IgA nephropathy and found to be of prognostic value. Recently, genetic studies have identified IgA nephropathy-associated loci. Within these loci are genes encoding products involved in complement regulation and interaction with immune complexes. Put together, these data identify the complement cascade as a rational treatment target for this chronic kidney disease. Recent case reports on the successful use of humanized anti-C5 monoclonal antibody eculizumab are consistent with this hypothesis, but a better understanding of the role of complement in IgA nephropathy is needed to guide future therapeutic interventions.

NLRC5: potential novel non-invasive biomarker for predicting and reflecting the progression of IgA nephritis

BACKGROUND

The nucleotide oligomerization domain-like receptor subfamily C5 (NLRC5) is primarily expressed in the adaptive and innate immune systems. NLRC5 was recently discovered to regulate immunity and inflammatory responses. Abnormal immune and inflammatory responses are considered critical pathogenesis in IgA nephritis (IgAN). However, the role of NLRC5 in IgAN is unknown. We previously showed that NLRC5 can be detected in patients with IgAN; herein, we further examined the pathophysiological significance of NLRC5 in the serum and renal deposits of patients with IgAN. This study is the first to find that NLRC5 is closely correlated with IgAN.

METHODS

IgAN patients (n = 50) who were diagnosed by renal biopsy provided blood and renal biopsy tissue, and age-matched healthy control subjects (blood donators n = 22; tissue donators n = 5) were included. Renal biopsies were diagnosed, and blood biochemical parameters were tested. Serum creatinine, urea, proteinuria, haematuria, albumin, and immunoglobulin A levels were recorded. Serum NLRC5 concentrations were detected by enzyme-linked immunosorbent assay, and tissue NLRC5 expression in kidney tissue was detected by immunohistochemical analysis. ROC curve analysis was used to evaluate the diagnostic value of the serum NLRC5 concentration in IgAN.

RESULTS

Serum NLRC5 concentration was significantly decreased in the IgAN group compared to that in the healthy control group (P < 0.0001), especially in S1 (Oxford classification) patients (P < 0.0001). Furthermore, serum NLRC5 concentration had a negative correlation with Lee's grade (r = 0.3526, P = 0.0060) and proteinuria levels (r = 0.4571, P = 0.0004). Tissue NLRC5 expression was significantly increased in the IgAN group compared to that in the healthy control group (P < 0.0001); a more significant increase was identified in the S1 group (P < 0.05) and had a positive correlation with Lee's grade (r = 0.497, P < 0.0001). We proposed a cut-off value of 1415 pg/ml for serum NLRC5 concentration, which was able to predict IgAN with 77.27% sensitivity and 87.5% specificity.

CONCLUSIONS

Serum NLRC5 concentrations in IgAN are significantly decreased, and tissue NLRC5 expression is significantly increased in IgAN renal tissue, which is consistent with pathological severity. This finding suggests that NLRC5 could potentially be a diagnostic index and represents a prognostic factor in IgAN patients.

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.

Complement factor H-related proteins in IgA nephropathy-sometimes a gentle nudge does the trick

Complement activation probably contributes to glomerular inflammation and damage in IgA nephropathy. In this issue, 2 groups report that levels of factor H-related protein 1 are elevated in patients with IgA nephropathy and correlate with disease progression. These studies provide new evidence that the complement cascade is important to the pathogenesis of this disease. These results also suggest that factor H-related protein 1 levels may be useful for identifying those patients at high risk of disease progression.

Serum IgA/C3 and glomerular C3 staining predict severity of IgA nephropathy

BACKGROUND

The aim of this study was to determine whether serum immunoglobulin A/complement factor 3 (IgA/C3) ratio and glomerular C3 staining predict outcome in IgA nephropathy.

METHODS

We collected data for 44 IgA nephropathy children treated with multi-drug combination therapy. The children were retrospectively divided into four groups based on serum IgA/C3 ratio and glomerular C3 staining: group A, IgA/C3 ratio >2.68 (median) and glomerular C3 staining ≥2.0, n = 9; group B, IgA/C3 ratio >2.68 and glomerular C3 staining <2.0, n = 7; group C, IgA/C3 ratio <2.68 and glomerular C3 staining ≥2.0, n = 7; and group D, IgA/C3 ratio <2.68 and glomerular C3 staining <2.0, n = 21. Clinical features; pathology at the first and second renal biopsy and at the latest follow up; and prognosis were analyzed for the four groups.

RESULTS

At the most recent follow up, urinary protein excretion, incidence of hematuria, and serum creatinine in group A were all higher than in group D. At the second biopsy, crescent absence/presence ratio; mesangial hypercellularity, segmental glomerulosclerosis or adhesion, endocapillary hypercellularity, and tubular atrophy/interstitial fibrosis as well as crescents and global glomerulosclerosis (MESTCG) score; and clonicity index in group A were higher than in group D. All patients in group D had normal urine, and the prevalence of persistent nephropathy in group A was higher than in group D.

CONCLUSIONS

Serum IgA/C3 ratio and glomerular C3 staining can predict outcome in IgA nephropathy.

Progressive IgA Nephropathy Is Associated With Low Circulating Mannan-Binding Lectin-Associated Serine Protease-3 (MASP-3) and Increased Glomerular Factor H-Related Protein-5 (FHR5) Deposition

Introduction

IgA nephropathy (IgAN) is characterized by glomerular deposition of galactose-deficient IgA1 and complement proteins and leads to renal impairment. Complement deposition through the alternative and lectin activation pathways is associated with renal injury.

Methods

To elucidate the contribution of the lectin pathway to IgAN, we measured the 11 plasma lectin pathway components in a well-characterized cohort of patients with IgAN.

Results

M-ficolin, L-ficolin, mannan-binding lectin (MBL)-associated serine protease (MASP)-1 and MBL-associated protein (MAp) 19 were increased, whereas plasma MASP-3 levels were decreased in patients with IgAN compared with healthy controls. Progressive disease was associated with low plasma MASP-3 levels and increased glomerular staining for C3b/iC3b/C3c, C3d, C4d, C5b-9, and factor H-related protein 5 (FHR5). Glomerular FHR5 deposition positively correlated with glomerular C3b/iC3b/C3c, C3d, and C5b-9 deposition, but not with glomerular C4d. These observations, together with the finding that glomerular factor H (fH) deposition was reduced in progressive disease, are consistent with a role for fH deregulation by FHR5 in renal injury in IgAN.

Conclusion

Our data indicate that circulating MASP-3 levels could be used as a biomarker of disease severity in IgAN and that glomerular staining for FHR5 could both indicate alternative complement pathway activation and be a tissue marker of disease severity.

Increased C4 and decreased C3 levels are associated with a poor prognosis in patients with immunoglobulin A nephropathy: a retrospective study

BACKGROUND

An association between serum complement levels and poor renal prognosis in patients with immunoglobulin A nephropathy (IgAN) remains controversial.

METHODS

We conducted a retrospective study examining the relationship between serum complement levels and prognosis in patients with IgAN. Between 2009 and 2013, patients with biopsy-confirmed IgAN were identified from the Second Affiliated Hospital of Wenzhou Medical College, China, and various parameters were documented during follow-up until 2015. The definition of the primary endpoint was a decrease of estimated glomerular filtration rate (eGFR) more than 30% from their baseline levels.

RESULTS

A total of 403 patients (55.3% female, average 33.7 months of follow-up) were identified and enrolled, with the primary endpoint occurring in 39 (9.8%) patients. Among the patients selected, 202 (50.1%) received corticosteroid treatment alone or in combination with another immunosuppressant (GS group), while others did not receive immunosuppressive treatment (non-GS group). The incidence of the primary endpoint was slightly lower in the GS group compared to the non-GS group (7.0% versus 12.6%, p = 0.06). Multivariate Cox proportional-hazard regression analyses, adjusting for age, systolic and diastolic blood pressure, 24-h urine protein, and immunosuppressive therapy, showed that serum complement 4 (C4) levels (hazard ratio [HR] 2.4, 95% confidence interval [CI] 1.6-3.8, p < 0.001) and serum complement 3 (C3) levels (HR 0.6, 95% CI 0.2-0.6, p < 0.001) were significantly associated with a poor prognosis among patients with IgAN.

CONCLUSIONS

We demonstrated that an increase in serum C4, as well as a decrease in C3, was an important outcome determinant for patients with IgAN. Testing serum C3 and C4 levels might assist in predicting renal outcomes among these patients.

Circulating complement factor H-related proteins 1 and 5 correlate with disease activity in IgA nephropathy

IgA nephropathy (IgAN) is a common cause of chronic kidney disease and end-stage renal failure, especially in young people. Due to a wide range of clinical outcomes and difficulty in predicting response to immunosuppression, we need to understand why and identify which patients with IgAN will develop progressive renal impairment. A deletion polymorphism affecting the genes encoding the complement factor H-related protein (FHR)-1 and FHR-3 is robustly associated with protection against IgAN. Some FHR proteins, including FHR-1 and FHR-5, antagonize the ability of complement factor H (fH), the major negative regulator of the complement alternative pathway, to inhibit complement activation on surfaces, a process termed fH deregulation. From a large cohort of patients, we demonstrated that plasma FHR-1 and the FHR-1/fH ratio were elevated in IgAN and associated with progressive disease. Plasma FHR-1 negatively correlated with eGFR but remained elevated in patients with IgAN with normal eGFR. Serum FHR5 was slightly elevated in IgAN but did not correlate with eGFR. Neither FHR5 levels nor the FHR-5/fH ratio was associated with progressive disease. However, higher serum FHR-5 levels were associated with a lack of response to immunosuppression, the presence of endocapillary hypercellularity, and histology scores of disease severity (the Oxford Classification MEST score). Thus, FHR-1 and FHR-5 have a role in IgAN disease progression.

Targeting C3a/C5a receptors inhibits human mesangial cell proliferation and alleviates immunoglobulin A nephropathy in mice

Complement activation has a deep pathogenic influence in immunoglobulin (Ig)A nephropathy (IgAN). C3a and C5a, small cleavage fragments generated by complement activation, are key mediators of inflammation. The fragments exert broad proinflammatory effects by binding to specific receptors (C3aR and C5aR, respectively). However, no studies thus far have investigated the effects of C3a, C5a and their receptors on IgAN. We observed that C3aR and C5aR antagonists repressed IgA-induced cell proliferation and interleukin (IL)-6 and monocyte chemotactic protein 1 (MCP-1) production in cultured human mesangial cells (HMCs). Furthermore, an IgAN mouse model induced by Sendai virus infection was employed to investigate the effects of C3aR and C5aR on IgAN in vivo for the first time. Wild-type (WT) and several knock-out mouse strains (C3aR^-/- or C5aR^-/- ) were immunized intranasally with increasing doses of inactivated virus for 14 weeks and were subjected to two intravenous viral challenges during the time-period indicated. In the Sendai virus-induced IgAN model, C3aR/C5aR-deficient mice had significantly reduced proteinuria, lower renal IgA and C3 deposition, less histological damage and reduced mesangial proliferation compared with WT mice. Both C3aR deficiency and C5aR deficiency, especially C3aR deficiency, inhibited renal tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-β, IL-1β, IL-6 and MCP-1 expression significantly. However, C3aR/C5aR-deficient and WT mice with IgAN did not differ with respect to their blood urea nitrogen (BUN) and serum creatinine levels. Our findings provide further support for the idea that C3aR and C5aR are crucially important in IgAN, and suggest that pharmaceutically targeting C3aR/C5aR may hold promise for the treatment of IgAN.

The clinical course of IgA nephropathy after kidney transplantation and its management

Immunoglobulin (Ig) A nephropathy is one of the most common primary glomerulonephritides worldwide causing end stage renal disease in up to 20-40% of affected patients, nearly two decades post diagnosis. Kidney transplantation is the treatment of choice for patients with renal failure, secondary to glomerular diseases. However, IgA nephropathy has a strong tendency to recur in the graft, and although initially thought to be a benign condition, several reports of graft loss, due to recurrent IgA nephropathy, there have been over the last three decades. Overall graft survival has been significantly improved in kidney transplantation, as a result of reduced incidence of acute rejection, as more potent and more specific immunosuppressive agents are now available in clinical practice. Thus, the rates of IgA nephropathy and other glomerulonephritides recurrence are expected to increase, since graft survival has been improved. However, the reported incidence of IgA nephropathy recurrence in the graft varies substantially across centers, as a consequence of different levels of interest, diverse biopsy policies and differing durations of follow up, of the published studies. Notably, recurrence rates of patients receiving graft biopsies by clinical indication only, ranges from 13% to 50% with graft loss being between 1.3% and 16%. The aim of this review is to underline important pathogenetic insights of IgA nephropathy, describe the clinical course of the disease after kidney transplantation, with emphasis on the incidence of recurrence and the associated risk factors, and finally provide all available options for its management in transplant recipients.

Fine Mapping Implicates a Deletion of CFHR1 and CFHR3 in Protection from IgA Nephropathy in Han Chinese

An intronic variant at the complement factor H (CFH) gene on chromosome 1q32 (rs6677604) associates with risk of IgA nephropathy (IgAN), but the association signal has not been uniformly replicated in Han Chinese populations. We investigated whether the causal sequence variant resides in the CFH gene or the neighboring complement factor H-related 1 (CFHR1) gene and CFHR3, which harbor an 84-kb combined deletion (CFHR3,1Δ) in linkage disequilibrium with rs6677604. Imputation of 1000 Genomes Project data did not suggest new causal single-nucleotide variants within the CFH cluster. We next performed copy number analysis across the CFH locus in two independent Han Chinese case-control cohorts (combined n=3581). The CFHR3,1Δ and rs6677604-A alleles were rare (4.4% in patients and 7.1% in controls) and in strong linkage disequilibrium with each other (r²=0.95); of these alleles, CFHR3,1Δ associated more significantly with decreased risk of IgAN (odds ratio [OR], 0.56; 95% confidence interval [95% CI], 0.46 to 0.70; P=8.5 × 10^-8 versus OR, 0.61; 95% CI, 0.50 to 0.75; P=1.6 × 10^-6 for rs6677604-A). Moreover, CFHR3,1Δ explained all of the association signal at rs6677604 and remained significant after conditioning on rs6677604 genotype (P=0.01). Exploratory analyses of clinical and histopathologic parameters using the Oxford classification criteria revealed a suggestive association of CFHR3,1Δ with reduced tubulointerstitial injury (OR, 0.46; 95% CI, 0.25 to 0.79). These data indicate that dysregulated activity of the alternative complement pathway contributes to IgAN pathogenesis in both Asians and Europeans and implicate CFHR3,1Δ as the functional allele at this locus.

IgA nephropathy in Brazil: apropos of 600 cases

IgA nephropathy (IgAN) is th e commonest primary glomerular disease worldwide. Studies on its prevalence in Brazil are however scarce. Databases and clinical records from 10 reference centres were retrospectively reviewed. Clinical and laboratory features at the moment of the biopsy were retrieved (age, gender, presence of hematuria, serum creatinine [mg/dL], proteinuria [g/24 h]). Renal biopsy findings were classified according to Haas single grade classification scheme and the Oxford Classification of IgAN. 600 cases of IgAN were identified, of which 568 (94.7 %) were on native kidneys. Male to female ratio was 1.24:1. Patients averaged 32.76 ± 15.12 years old (range 4–89, median 32). Proteinuria and hematuria were observed, respectively in 56.63 and 72.29 % of patients. The association of both these findings occurred in 37.95 % of the cases. Serum creatinine averaged 1.65 ± 0.67 mg/dL (median 1.5 mg/dL) at diagnosis. Segmental sclerosis and mesangial hypercellularity were the main glomerular findings (47.6 and 46.2 %) The commonest combination by Oxford Classification of IgAN, was M0 E0 S0 T0 (22.4 %). Chronic tubulo-interstitial lesions with an extension wider than 25 % of the renal cortex could be identified in 32.2 % of the cases. Tubular atrophy and interstitial fibrosis were more strongly associated with higher 24-h proteinuria and serum creatinine levels. Segmental sclerosis (S1) showed a stronger tendency of association with the presence of tubulo-interstitial lesions (T1 and T2) than other glomerular variables. To the best of our knowledge this is the largest series of IgAN in Brazil. It depicts the main biopsy findings and their possible clinical correlates. Our set of data is comparable to previous reports.

Immunoglobulin A nephropathy: current progress and future directions

Immunoglobulin A (IgA) nephropathy is the most prevalent form of primary glomerulonephritis that often leads to end-stage kidney failure, thereby representing a major health challenge worldwide. Tremendous effort has been dedicated to the diagnosis, monitoring, and treatment of the disease, and the past several years have witnessed exciting advances that have enriched our understanding of the biology, etiology, and pathology of IgA nephropathy. The disease is characterized by predominant deposition of IgA immune complexes that progressively causes activation of mesangial cells, glomerular inflammation, and ultimately renal injury. Multiple recent independent high-throughput studies in cohorts have identified key susceptibility alleles, such as the major histocompatibility complex loci that are significantly associated with the risk of disease occurrence. Notably, a fraction of these risk loci encode proteins that participate in immune defense against mucosal pathogens, particularly intestinal nematodes, indicating a linkage between IgA-mediated antihelminth immunity and the pathogenesis of IgA nephropathy. The emerging "omics" technology also allows for systemic analysis of urinary and serum samples as a noninvasive procedure for diagnosis and prognosis, as demonstrated by several studies implicating the proteomic signature and microRNA profile as promising diagnostic and prognostic parameters. In the clinic, the current treatment protocol relies on suppression of the renin-angiotensin system to control blood pressure and proteinuria. This review scrutinizes and summarizes recent relevant findings that aim to translate researchers' benchside knowledge of disease initiation and development into patients' bedside diagnosis and therapy.