Membranous nephropathy (MN) is an autoimmune disease that is caused by the production of autoantibody against glomerular podocyte antigens by immune cells due to the lack of self-tolerance mechanisms. Similar to many autoimmune diseases, the pathogenesis of MN is still vague and many experiments are being conducted to detect the antigens and genetic reasons for MN illness. Recently, new antigens, such as exotosin 1/exotosin 2, neural EGF-like-1, semaphorin 3B, and protocadherin 7 have been identified in MN patients who did not have presence of antiphospholipase A2 receptor antigen. What is more, cytokines, which are molecules that regulate immune responses, have been found to have harmful effects in various autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and MN. The role of cytokines and treatment strategies in MN patients is discussed in this article. As the understanding of the disease improves, targeted therapies that focus on specific antigens or cytokines may be developed to effectively manage MN.

Complement-mediated kidney diseases encompass a complex group of diseases that are primarily caused by dysregulation of the complement system. The complement system is a crucial component of the innate immune system consisting of soluble and membrane-bound proteins. The complement system is essential for the defence against pathogens and homeostasis but its uncontrolled activation can lead to an exaggerated cellular response to immunogenic, inflammatory and metabolic stimuli. For example, glomerular deposition of immune complexes can activate the complement system and contribute to the progression of kidney diseases. The most well-known complement-mediated kidney diseases are atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy, which falls under the group of membranoproliferative glomerulonephritis (MPGN). Diagnosing these diseases requires detailed investigations with respect to triggering factors, including genetic analyses and the measurement of specific complement factors. New therapeutic approaches with drugs targeting complement system activation are now offering promising treatment options. These medications fundamentally differ from other immunosuppressive drugs and specifically target the pathological processes within the complement system. This article provides an overview of the mechanisms of complement regulation, the pathophysiological foundations of complement-mediated kidney diseases and the latest diagnostic and therapeutic advances. The goal is to provide a deeper understanding of these complex conditions and to emphasize the importance of an interdisciplinary approach in treatment and research.

Relapse after initial remission reduces renal survival in patients with primary membranous nephropathy (PMN). In this study, we aim to identify risk factors of relapse in PMN and construct a model to identify patients at high risk of relapse early.

We conducted a multi-center retrospective study using the China Renal Data System database, which includes data from 24 urban academic centers across China. A prediction model based on the Cox proportional hazards model was derived in the derivation group and validated in the validation group.

515 patients with biopsy-proven PMN achieving initial remission were enrolled. 32.62% of patients subsequently relapsed during a median of 6.08 months. Lower serum albumin (Alb) (per 1 g/L decrease, hazard ratio [HR] =1.48, 95% confidence interval [CI] 1.29-1.78, p < 0.001), lower estimated glomerular filtration rate (eGFR) (per 10 mL/min/1.73m2 decrease, HR =1.14, 95% CI 0.97-1.49, p < 0.001), higher serum complement 4 (C4) (per 0.1 g/L increase, HR =1.89, 95% CI 1.32-3.22, p = 0.012), partial remission (PR) (HR =2.28, 95%CI 1.74-4.04, p < 0.001), and treatment with calcineurin inhibitors (CINs) (HR =1.33, 95%CI 1.04-1.64, p < 0.001) at the time of remission were risk factors for relapse. C-statistic, time-dependent areas under the receiver operating characteristic curve, and calibration plots confirmed that the model had excellent discrimination and calibration in predicting PMN relapse. The anti-phospholipase A2 receptor antibody (aPLA2Rab) titers and pathologic features did not substantially improve the model.

Our study confirms the well-known low Alb and eGFR, PR, and treatment of CNIs at the time of remission as risk factors for PMN relapse, but aPLA2Rab and pathologic features may not predict relapse. In addition, it is the first study to show serum C4 is associated with PMN relapse. We suggest that complement-targeted therapies may be a potential therapy to prevent PMN relapse.

Primary membranous nephropathy (PMN) is an immune-mediated glomerular disease. Rituximab (RTX) is recommended as a first-line immunosuppressive therapy and shows high clinical efficacy, but the optimal doses remain controversial. Approximately 20%-40% of PMN patients experience RTX resistance and failure. Reduced bioavailability, RTX internalization and attack, anti-RTX antibody production, autoreactive B-cell reservoirs and chronic and irreversible renal damage may contribute to this problem. Therefore, new treatment modalities are needed to compensate for this deficit. New interventions and new dose combinations are being proposed. Multiple drug combination therapies show comparable clinical efficacy to conventional treatments by blocking the production of disease-causing antibodies in multiple directions, and can reduce single-agent doses without increasing adverse effects. New therapies that directly target B cells, plasma cells, and antibody production have shown encouraging results. In addition, new techniques for sweeping antibodies and chimeric antigen receptor T-cell therapy also may be promising strategies for PMN. Immunoadsorption could be used as an auxiliary choice for severe cases. This article explores new treatments for PMN and highlights possible mechanisms for potential new technologies that offer new ideas for treatment.

COVID-19 has been reported to be associated with the occurrence and recurrence of membranous nephropathy (MN). The clinicopathological characteristics and complement system activation of MN after COVID-19 are unclear.

A total of 38 patients with biopsy-proven MN who developed new-onset proteinuria after COVID-19 were enrolled in this study. One hundred patients with primary MN diagnosed before the COVID-19 pandemic were the control. Renal immunohistochemical staining for SARS-CoV-2 nucleocapsid protein was performed in 38 patients with MN after COVID-19. Serum membrane attack complex (MAC) was detected by enzyme-linked immunosorbent assay. Glomerular staining for the complement proteins in different pathways were detected by immunohistochemistry.

Thirteen of 38 patients had positive staining for SARS-CoV-2 nucleocapsid protein. Compared with the control patients, the clinical manifestations were more severe in patients after COVID-19. Patients with positive SARS-CoV-2 staining had a higher proportion of nephrotic syndrome, lower level of serum albumin, and greater severity of renal interstitial fibrosis than those of patients with negative SARS-CoV-2 staining. Serum MAC level and renal MAC staining intensity of MN after COVID-19 were significantly higher than those of the control patients. MAC expression in MN patients with positive SARS-CoV-2 staining was stronger than that in both control patients and MN after COVID-19 with negative SARS-CoV-2 staining. The expression trend of factor H was consistent with that of MAC.

Excessive activation of the complement system aggravated symptoms in MN after COVID-19. Therapeutic strategy targeting the complement system may need to be considered.

Primary membranous nephropathy (PMN) is a predominant cause of adult nephrotic syndrome, with its incidence witnessing a progressive surge over time. Approximately 35% to 47% of patients progress to renal failure within 10 years, causing a huge social burden. Within China, the proportion of PMN in primary glomerular disease exhibits a gradual ascension. Recent studies have shown that the 3 activation pathways of complement: the classical pathway, mannose-binding lectin pathway, and alternative pathway, are all involved in the pathogenesis of PMN. Despite historical limitations in detecting C1q deposits on the glomeruli of PMN in the past, recent studies have confirmed the classical pathway is implicated in patients with PMN. Considering the dysregulation of the complement system has been observed in PMN, complement inhibitors become increasingly promising. Several clinical trials are presently underway to evaluate the efficacy of complement inhibitors, such as MASP2 antagonists (OMS721), C3 and C3b antagonists (APL2), FD inhibitors (BCX9930), C3aR antagonists (SB290157 and JR14a), FB inhibitors (LNP023). This article reviews the recent research progress on the role of the complement pathway in the pathogenesis of PMN, and underscores the importance of continued research into the complement pathway and its inhibitors, which may pave the way for groundbreaking advancements in the management of PMN.

Diabetic kidney disease is one of the most severe chronic microvascular complications of diabetes and a primary cause of end-stage renal disease. Clinical studies have shown that renal inflammation is a key factor determining kidney damage during diabetes. With the development of immunological technology, many studies have shown that diabetic nephropathy is an immune complex disease, and that most patients have immune dysfunction. However, the immune response associated with diabetic nephropathy and autoimmune kidney disease, or caused by ischemia or infection with acute renal injury, is different, and has a com-plicated pathological mechanism. In this review, we discuss the pathogenesis of diabetic nephropathy in immune disorders and the intervention mechanism, to provide guidance and advice for early intervention and treatment of diabetic nephropathy.

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.

Membranous nephropathy (MN) occurs predominantly in middle-aged and elderly individuals and ranks among the most prevalent etiologies of elderly nephrotic syndrome. As an autoimmune glomerular disorder characterized by glomerular basement membrane thickening and immune complex deposition, conventional MN animal models, including the Heymann nephritis rat model and the c-BSA mouse model, have laid a foundation for MN pathogenesis research. However, differences in target antigens between rodents and humans have impeded this work. In recent years, researchers have created antigen-specific MN animal models, primarily centered on PLA2R1 and THSD7A, employing diverse techniques that provide innovative in vivo research platforms for MN. Furthermore, significant advancements have been made in the development of in vitro podocyte models relevant to MN. This review compiles recent antigen-specific MN animal models and podocyte models, elucidates their immune responses and pathological characteristics, and offers insights into the future of MN experimental model development. Our aim is to provide a comprehensive resource for research into the pathogenesis of MN and the development of targeted therapies for older patients with MN to prolong lifespan and improve quality of life.

Membranous nephropathy is an autoimmune disease affecting the glomeruli and is one of the most common causes of nephrotic syndrome. In the absence of any therapy, 35% of patients develop end-stage renal disease. The discovery of autoantibodies such as phospholipase A2 receptor 1, antithrombospondin and neural epidermal growth factor-like 1 protein has greatly helped us to understand the pathogenesis and enable the diagnosis of this disease and to guide its treatment. Depending on the complications of nephrotic syndrome, patients with this disease receive supportive treatment with diuretics, ACE inhibitors or angiotensin-receptor blockers, lipid-lowering agents and anticoagulants. After assessing the risk of progression of end-stage renal disease, patients receive immunosuppressive therapy with various drugs such as cyclophosphamide, steroids, calcineurin inhibitors or rituximab. Since immunosuppressive drugs can cause life-threatening side effects and up to 30% of patients do not respond to therapy, new therapeutic approaches with drugs such as adrenocorticotropic hormone, belimumab, anti-plasma cell antibodies or complement-guided drugs are currently being tested. However, special attention needs to be paid to the choice of therapy in secondary forms or in specific clinical contexts such as membranous disease in children, pregnant women and patients undergoing kidney transplantation.

Primary membranous nephropathy (PMN) has a heterogeneous natural course. Immunosuppressive therapy is recommended for PMN patients at moderate or high risk of renal function deterioration. Prediction models for the treatment failure of PMN have rarely been reported.

This study retrospectively studied patients diagnosed as PMN by renal biopsy at Sichuan Provincial People's Hospital from January 2017 to December 2020. Information on clinical characteristics, laboratory test results, pathological examination, and treatment was collected. The outcome was treatment failure, defined as the lack of complete or partial remission at the end of 12 months. Simple logistic regression was used to identify candidate predictive variables. Forced-entry stepwise multivariable logistic regression was used to develop the prediction model, and performance was evaluated using C-statistic, calibration plot, and decision curve analysis. Internal validation was performed by bootstrapping.

In total, 310 patients were recruited for this study. 116 patients achieved the outcome. Forced-entry stepwise multivariable logistic regression indicated that PLA2Rab titer (OR = 1.002, 95% CI: 1.001-1.004, p = 0.003), inflammatory cells infiltration (OR = 2.753, 95% CI: 1.468-5.370, p = 0.002) and C3 deposition on immunofluorescence (OR = 0.217, 95% CI: 0.041-0.964, p = 0.049) were the three independent risk factors for treatment failure of PMN. The final prediction model had a C-statistic (95% CI) of 0.653 (0.590-0.717) and a net benefit of 23%-77%.

PLA2R antibody, renal interstitial inflammation infiltration, and C3 deposition on immunofluorescence were the three independent risk factors for treatment failure in PMN. Our prediction model might help identify patients at risk of treatment failure; however, the performance awaits improvement.

Mannan-binding lectin (MBL) is a main component of the lectin pathway of the complement system. Although there are some studies showing links between endocrine and immune systems, the ones concerning hypopituitarism are limited. The aim of this study was to check whether there is any association between blood MBL level and pituitary hormone deficiencies and whether this relationship is affected by appropriate hormone replacement therapies.

One hundred and twenty (120) inpatients, aged 18-92, were divided into two main groups, i.e. control individuals (21/120) and patients with pituitary diseases (99/120). The latter were diagnosed either with hypopituitarism (n=42) or with other pituitary diseases (not causing hypopituitarism) (n=57). Additionally, hypopituitary patients on appropriate replacement therapies (compensated hypopituitarism) were compared to patients on inappropriate replacement therapies (non-compensated hypopituitarism). Several parameters in blood serum were measured, including MBL level, pituitary and peripheral hormones and different biochemical parameters.

Serum MBL level was significantly lower in patients with hypopituitarism comparing to controls (1358.97 ± 244.68 vs. 3199.30 ± 508.46, p<0.001) and comparing to other pituitary diseases (1358.97 ± 244.68 vs. 2388.12 ± 294.99, p=0.015) and this association was confirmed by univariate regression analysis. We evaluated the distribution of patients with relation to MBL level; there was a clear difference in this distribution between control individuals (among whom no subjects had MBL level <500 ng/mL) and patients with hypopituitarism (among whom 43% of patients had MBL level <500 ng/mL). Moreover, patients with non-compensated hypopituitarism had lower mean and median MBL levels comparing to patients with compensated hypopituitarism (1055.38 ± 245.73 vs. 2300.09 ± 579.93, p=0.027; 488.51 vs. 1951.89, p=0.009, respectively) and this association was confirmed in univariate regression analysis. However, mean and median MBL levels in patients with compensated hypopituitarism vs. controls did not differ significantly (2300.09 ± 579.93 vs. 3199.30 ± 508.46, p=0.294; 1951.90 vs. 2329.16; p=0.301, respectively).

Hypopituitarism in adults is associated with a decreased blood concentration of mannan-binding lectin, a phenomenon which does not exist in hypopituitary patients on the appropriate hormone replacement therapies. Therefore measurement of mannan-binding lectin level in patients with hypopituitarism may be considered as a parameter contributing to adjust optimal doses of hormone replacement therapies.