The genetics and immunobiology of IgA nephropathy

Unraveling chronic kidney disease in children: a surprising manifestation of celiac disease

Celiac disease, firstly described in children, is a type of T-cell enteropathy that occurs in individuals genetically predisposed to gluten exposure. The estimated global prevalence of celiac disease is continuously increasing. Although, traditionally, celiac disease was diagnosed in children with failure to thrive and digestive issues, it is now recognized that may present with a wide range of symptoms beyond gastrointestinal ones. Celiac disease continues to pose significant challenges due to the continuous advancement of knowledge in understanding its pathophysiology, diagnosing the condition, managing its effects, and exploring potential therapeutic approaches. The prevalence of celiac disease is increased among individuals with chronic kidney disease, also. The most frequent associations are with diabetic nephropathy, IgA nephropathy and urolithiasis. A gut-kidney axis has been recognized to play a significant role in chronic kidney diseases. This literature review aims to review the chronic renal pathology associated with celiac disease, with emphasis on childhood.

Efficacy and safety of biologic agents for IgA nephropathy: A protocol for systematic review and meta-analysis

BACKGROUND

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide and a leading cause of chronic kidney failure. There are currently no definitive therapeutic regimens to treat or prevent the progression of IgAN. However, biologic agents offer novel therapeutic approaches that target immunological mechanisms to slow or halt disease progression. The objective of this study is to evaluate the efficacy and safety of biologic agents in patients with IgA nephropathy.

METHODS

We will systematically search PubMed, EMbase, Web of Science, Cochrane Library, and www.clinicaltrials.gov for randomized controlled trials of biologic agents for the treatment of IgA nephropathy. The search period will span from the establishment of each database until October 2023. The quality assessment of included studies will be performed individually using the revised Cochrane risk-of-bias tool for randomized trials (RoB 2), and meta-analysis will be conducted using Revman 5.4.1 software.

CONCLUSIONS

The results of this study will provide evidence-based medical evidence for the clinical application of biologic agents in patients with IgA nephropathy.

PROSPERO REGISTRATION NUMBER

CRD42023400450.

LIF/JAK2/STAT1 Signaling Enhances Production of Galactose-Deficient IgA1 by IgA1-Producing Cell Lines Derived From Tonsils of Patients With IgA Nephropathy

Introduction

Galactose-deficient IgA1 (Gd-IgA1) plays a key role in the pathogenesis of IgA nephropathy (IgAN). Tonsillectomy has been beneficial to some patients with IgAN, possibly due to the removal of tonsillar cytokine-activated cells producing Gd-IgA1. To test this hypothesis, we used immortalized IgA1-producing cell lines derived from tonsils of patients with IgAN or obstructive sleep apnea (OSA) and assessed the effect of leukemia inhibitory factor (LIF) or oncostatin M (OSM) on Gd-IgA1 production.

Methods

Gd-IgA1 production was measured by lectin enzyme-linked immunosorbent assay; JAK-STAT signaling in cultured cells was assessed by immunoblotting of cell lysates; and validated by using small interfering RNA (siRNA) knock-down and small-molecule inhibitors.

Results

IgAN-derived cells produced more Gd-IgA1 than the cells from patients with OSA, and exhibited elevated Gd-IgA1 production in response to LIF, but not OSM. This effect was associated with dysregulated STAT1 phosphorylation, as confirmed by STAT1 siRNA knock-down. JAK2 inhibitor, AZD1480 exhibited a dose-dependent inhibition of the LIF-induced Gd-IgA1 overproduction. Unexpectedly, high concentrations of AZD1480, but only in the presence of LIF, reduced Gd-IgA1 production in the cells derived from patients with IgAN to that of the control cells from patients with OSA. Based on modeling LIF-LIFR-gp130-JAK2 receptor complex, we postulate that LIF binding to LIFR may sequester gp130 and/or JAK2 from other pathways; and when combined with JAK2 inhibition, enables full blockade of the aberrant O-glycosylation pathways in IgAN.

Conclusion

In summary, IgAN cells exhibit LIF-mediated overproduction of Gd-IgA1 due to abnormal signaling. JAK2 inhibitors can counter these LIF-induced effects and block Gd-IgA1 synthesis in IgAN.

Novel Antigens and Clinical Updates in Membranous Nephropathy

Membranous nephropathy (MN), an autoimmune kidney disease and leading cause of nephrotic syndrome, leads to kidney failure in up to one-third of affected individuals. Most MN cases are due to an autoimmune reaction against the phospholipase A2 receptor (PLA2R) located on kidney podocytes. Serum PLA2R antibody quantification is now part of routine clinical practice because antibody titers correlate with disease activity and treatment response. Recent advances in target antigen detection have led to the discovery of more than 20 other podocyte antigens, yet the clinical impact of additional antigen detection remains unknown and is under active investigation. Here we review recent findings and hypothesize how current research will inform future care of patients with MN.

Glomerular spatial transcriptomics of IgA nephropathy according to the presence of mesangial proliferation

Mesangial proliferation is a diagnostic feature and a prognostic predictor of immunoglobulin A nephropathy (IgAN). We aimed to investigate the gene expression profiles of IgAN glomerulus according to the presence of mesangial proliferation. We performed spatial-specific transcriptomic profiling on kidney biopsy tissues using the GeoMx Digital Spatial Profiler. Twelve cases with three glomeruli for each case were profiled using direct pathologic classification (4 M1-IgAN, 4 M0-IgAN, and 4 donor controls). The results of enriched glom-specific genes demonstrated that M1-IgAN could be distinguished from controls (77 upregulated and 55 downregulated DEGs), while some DEGs were identified between M1-IgAN and M0-IgAN cases (24 upregulated and 8 downregulated DEGs) or between M0 and controls (1 upregulated and 16 downregulated DEGs). TCF21, an early podocyte damage marker, was the only differentially expressed gene (DEG) consistently upregulated in both M1-IgAN and M0-IgAN patients, whereas ATF3, EGR1, DUSP1, FOS, JUNB, KLF2, NR4A1, RHOB, and ZFP36 were consistently downregulated in IgAN cases. Glomeruli from M1-IgAN cases were significantly enriched for cell surface/adhesion molecules and gene expressions associated with vascular development or the extracellular matrix. Spatial transcriptomic analysis may contribute to dissecting structure-specific pathophysiology and molecular changes in IgAN.

A Phase 2 Trial of Sibeprenlimab in Patients with IgA Nephropathy

BACKGROUND

A proliferation-inducing ligand (APRIL) is implicated in the pathogenesis of IgA nephropathy. Sibeprenlimab is a humanized IgG2 monoclonal antibody that binds to and neutralizes APRIL.

METHODS

In this phase 2, multicenter, double-blind, randomized, placebo-controlled, parallel-group trial, we randomly assigned adults with biopsy-confirmed IgA nephropathy who were at high risk for disease progression, despite having received standard-care treatment, in a 1:1:1:1 ratio to receive intravenous sibeprenlimab at a dose of 2, 4, or 8 mg per kilogram of body weight or placebo once monthly for 12 months. The primary end point was the change from baseline in the log-transformed 24-hour urinary protein-to-creatinine ratio at month 12. Secondary end points included the change from baseline in the estimated glomerular filtration rate (eGFR) at month 12. Safety was also assessed.

RESULTS

Among 155 patients who underwent randomization, 38 received sibeprenlimab at a dose of 2 mg per kilogram, 41 received sibeprenlimab at a dose of 4 mg per kilogram, 38 received sibeprenlimab at a dose of 8 mg per kilogram, and 38 received placebo. At 12 months, the geometric mean ratio reduction (±SE) from baseline in the 24-hour urinary protein-to-creatinine ratio was 47.2±8.2%, 58.8±6.1%, 62.0±5.7%, and 20.0±12.6% in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. At 12 months, the least-squares mean (±SE) change from baseline in eGFR was -2.7±1.8, 0.2±1.7, -1.5±1.8, and -7.4±1.8 ml per minute per 1.73 m2 in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. The incidence of adverse events that occurred after the start of administration of sibeprenlimab or placebo was 78.6% in the pooled sibeprenlimab groups and 71.1% in the placebo group.

CONCLUSIONS

In patients with IgA nephropathy, 12 months of treatment with sibeprenlimab resulted in a significantly greater decrease in proteinuria than placebo. (Funded by Visterra; ENVISION ClinicalTrials.gov number, NCT04287985; EudraCT number, 2019-002531-29.).

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.

Current Understanding of Complement Proteins as Therapeutic Targets for the Treatment of Immunoglobulin A Nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and a frequent cause of kidney failure. Currently, the diagnosis necessitates a kidney biopsy, with routine immunofluorescence microscopy revealing IgA as the dominant or co-dominant immunoglobulin in the glomerular immuno-deposits, often with IgG and sometimes IgM or both. Complement protein C3 is observed in most cases. IgAN leads to kidney failure in 20-40% of patients within 20 years of diagnosis and reduces average life expectancy by about 10 years. There is increasing clinical, biochemical, and genetic evidence that the complement system plays a paramount role in the pathogenesis of IgAN. The presence of C3 in the kidney immuno-deposits differentiates the diagnosis of IgAN from subclinical glomerular mesangial IgA deposition. Markers of complement activation via the lectin and alternative pathways in kidney-biopsy specimens are associated with disease activity and are predictive of poor outcome. Levels of select complement proteins in the circulation have also been assessed in patients with IgAN and found to be of prognostic value. Ongoing genetic studies have identified at least 30 loci associated with IgAN. Genes within some of these loci encode complement-system regulating proteins that can interact with immune complexes. The growing appreciation for the central role of complement components in IgAN pathogenesis highlighted these pathways as potential treatment targets and sparked great interest in pharmacological agents targeting the complement cascade for the treatment of IgAN, as evidenced by the plethora of ongoing clinical trials.

The incidence and prevalence of IgA nephropathy in Europe

BACKGROUND

This study aimed to determine the incidence and prevalence of immunoglobulin A nephropathy (IgAN) in Europe based on high-quality data from national registries.

METHODS

IgAN incidences were obtained from a literature review of European studies of national kidney biopsy registry data in which IgAN diagnosis was biopsy-verified using contemporary techniques. Studies were eligible for the main analysis if published from 1990 to 2020. IgAN point prevalence was defined as the annual IgAN incidence multiplied by the estimated duration of disease. Incidence and prevalence estimates were made for three pooled populations: (i) patients of all ages; (ii) pediatric patients; and (iii) elderly patients.

RESULTS

Across 10 European countries, the estimated annual IgAN incidence was 0.76 per 100 000 in patients of all ages. The corresponding pooled IgAN point prevalence was 2.53 per 10 000 (95% confidence interval: 2.51-2.55), ranging from 1.14 per 10 000 in Spain to 5.98 per 10 000 in Lithuania. Applied to 2021 population estimates, the number of expected prevalent IgAN cases was 47 027 across all 10 countries and ranged from 577 in Estonia to 16 645 in Italy. Among pediatric patients, IgAN incidence was 0.20 per 100 000 children and IgAN point prevalence was 0.12 per 10 000 children. Among elderly patients, IgAN incidence was 0.30 per 100 000 and IgAN point prevalence was 0.36 per 10 000.

CONCLUSIONS

Based on high-quality data from European national registries, IgAN point prevalence was estimated at 2.53 per 10 000 in patients of all ages. Prevalence was considerably lower in pediatric and elderly populations.

Efficacy and safety of a targeted-release formulation of budesonide in patients with primary IgA nephropathy (NefIgArd): 2-year results from a randomised phase 3 trial

BACKGROUND

IgA nephropathy is a chronic immune-mediated kidney disease and a major cause of kidney failure worldwide. The gut mucosal immune system is implicated in its pathogenesis, and Nefecon is a novel, oral, targeted-release formulation of budesonide designed to act at the gut mucosal level. We present findings from the 2-year, phase 3 NefIgArd trial of Nefecon in patients with IgA nephropathy.

METHODS

In this phase 3, multicentre, randomised, double-blind, placebo-controlled trial, adult patients (aged ≥18 years) with primary IgA nephropathy, estimated glomerular filtration rate (eGFR) 35-90 mL/min per 1·73 m2, and persistent proteinuria (urine protein-creatinine ratio ≥0·8 g/g or proteinuria ≥1 g/24 h) despite optimised renin-angiotensin system blockade were enrolled at 132 hospital-based clinical sites in 20 countries worldwide. Patients were randomly assigned (1:1) to receive 16 mg/day oral capsules of Nefecon or matching placebo for 9 months, followed by a 15-month observational follow-up period off study drug. Randomisation via an interactive response technology system was stratified according to baseline proteinuria (<2 or ≥2 g/24 h), baseline eGFR (<60 or ≥60 mL/min per 1·73 m2), and region (Asia-Pacific, Europe, North America, or South America). Patients, investigators, and site staff were masked to treatment assignment throughout the 2-year trial. Optimised supportive care was also continued throughout the trial. The primary efficacy endpoint was time-weighted average of eGFR over 2 years. Efficacy and safety analyses were done in the full analysis set (ie, all randomly assigned patients). The trial was registered on ClinicalTrials.gov, NCT03643965, and is completed.

FINDINGS

Patients were recruited to the NefIgArd trial between Sept 5, 2018, and Jan 20, 2021, with 364 patients (182 per treatment group) randomly assigned in the full analysis set. 240 (66%) patients were men and 124 (34%) were women, and 275 (76%) identified as White. The time-weighted average of eGFR over 2 years showed a statistically significant treatment benefit with Nefecon versus placebo (difference 5·05 mL/min per 1·73 m2 [95% CI 3·24 to 7·38], p<0·0001), with a time-weighted average change of -2·47 mL/min per 1·73 m2 (95% CI -3·88 to -1·02) reported with Nefecon and -7·52 mL/min per 1·73 m2 (-8·83 to -6·18) reported with placebo. The most commonly reported treatment-emergent adverse events during treatment with Nefecon were peripheral oedema (31 [17%] patients, vs placebo, seven [4%] patients), hypertension (22 [12%] vs six [3%]), muscle spasms (22 [12%] vs seven [4%]), acne (20 [11%] vs two [1%]), and headache (19 [10%] vs 14 [8%]). No treatment-related deaths were reported.

INTERPRETATION

A 9-month treatment period with Nefecon provided a clinically relevant reduction in eGFR decline and a durable reduction in proteinuria versus placebo, providing support for a disease-modifying effect in patients with IgA nephropathy. Nefecon was also well tolerated, with a safety profile as expected for a locally acting oral budesonide product.

FUNDING

Calliditas Therapeutics.

[Diagnosis and Treatment of IgA Nephropathy-2023]

Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis. It leads to end-stage kidney disease in about a third of the patients within 10 to 20 years. The pathogenesis of IgAN is incompletely understood. It is believed that a dysregulation of the mucosal immune system leads to undergalactosylation of IgA, followed by formation of IgG autoantibodies against undergalactosylated IgA, circulation of these IgG-IgA immune complexes, deposition of the immune complexes in the mesangium, ultimately resulting in glomerular inflammation. IgAN can occasionally be triggered by other diseases, these secondary causes of IgAN should be identified or ruled out (chronic inflammatory bowel disease, infections, tumors, rheumatic diseases). Characteristic findings of IgAN of variable extent are a nephritic urinary sediment (erythrocytes, acanthocytes, erythrocyte casts), proteinuria, impaired renal function, arterial hypertension, or intermittent painless macrohematuria, especially during infections of the upper respiratory tract. However, the diagnosis of IgAN can only be made by a kidney biopsy. A histological classification (MEST‑C score) should always be reported to be able to estimate the prognosis. The most important therapeutic measure is an optimization of the supportive therapy, which includes, among other things, a consistent control of the blood pressure, an inhibition of the RAS, and the administration of an SGLT2 inhibitor. A systemic immunosuppressive therapy with corticosteroids is discussed controversially, should be used restrictively and only administered after an individual benefit-risk assessment under certain conditions that speak for a progressive IgAN. New promising therapeutics are enteral Budesonide or the dual angiotensin-II-receptor- and endothelin-receptor-antagonist Sparsentan. Rapidly progressive IgAN should be treated with corticosteroids and cyclophosphamide like ANCA-associated vasculitis.

Treatment and outcome of IgA nephropathy in children from one single center experience

BACKGROUND

There is no standard recommendation for IgA nephropathy treatment in children.

METHODS

This is a retrospective study. From 2012 to 2020, newly diagnosed primary IgAN followed up for at least 1 year were enrolled. The correlation of MESTC scores and clinical index including proteinuria, gross hematuria and renal dysfunction was analyzed. Treatment and clinical response of 6 month, 1year and 3 year at follow up were also analyzed. Complete renal remission was calculated with Kaplan-Meier analysis.

RESULTS

The median follow up was 36 months, from 12 months to 87months in 40 IgAN children. Angiotensin-converting enzyme inhibitor (ACEI) was applied to all patients. 30% received ACEI alone; 15% received glucocorticoids; 37.5% received glucocorticoids plus cyclophosphamide, 17.5% received glucocorticoids plus mycophenolate mofetil. Individuals with diffuse mesangial hypercellularity (M1) were more likely to have nephrotic range proteinuria compared to patients with M0 (80% vs. 20%, P < 0.01). Complete renal remission at 6-month, 1-year and 3-year follow up is 50.25%, 70% and 87.5% respectively. Five-year complete renal remission calculated by Kaplan-Meier analysis is 58.4%. Although without significant difference, there is trend of better survival with complete renal remission in group of nephrotic range proteinuria onset. There is no severe adverse effect.

CONCLUSION

This study supports the use of glucocorticoids plus immunosuppressive in addition to ACEI in IgA nephrology pediatric patients with proteinuria. We suggest proactive immunosuppressive treatment in IgA nephropathy in children. This is from a single center in China as may not same results in other population.

Macrophage Function Modulated by tPA Signaling in Mouse Experimental Kidney Disease Models

Macrophage infiltration and accumulation is a hallmark of chronic kidney disease. Tissue plasminogen activator (tPA) is a serine protease regulating the homeostasis of blood coagulation, fibrinolysis, and matrix degradation, and has been shown to act as a cytokine to trigger various receptor-mediated intracellular signal pathways, modulating macrophage function in response to kidney injury. In this review, we discuss the current understanding of tPA-modulated macrophage function and underlying signaling mechanisms during kidney fibrosis and inflammation.

IgA antibody immunotherapy targeting GD2 is effective in preclinical neuroblastoma models

BACKGROUND

Immunotherapy targeting GD2 is very effective against high-risk neuroblastoma, though administration of anti-GD2 antibodies induces severe and dose-limiting neuropathic pain by binding GD2-expressing sensory neurons. Previously, the IgG1 ch14.18 (dinutuximab) antibody was reformatted into the IgA1 isotype, which abolishes neuropathic pain and induces efficient neutrophil-mediated antibody-dependent cellular cytotoxicity (ADCC) via activation of the Fc alpha receptor (FcαRI/CD89).

METHODS

To generate an antibody suitable for clinical application, we engineered an IgA molecule (named IgA3.0 ch14.18) with increased stability, mutated glycosylation sites and substituted free (reactive) cysteines. The following mutations were introduced: N45.2G and P124R (CH1 domain), C92S, N120T, I121L and T122S (CH2 domain) and a deletion of the tail piece P131-Y148 (CH3 domain). IgA3.0 ch14.18 was evaluated in binding assays and in ADCC and antibody-dependent cellular phagocytosis (ADCP) assays with human, neuroblastoma patient and non-human primate effector cells. We performed mass spectrometry analysis of N-glycans and evaluated the impact of altered glycosylation in IgA3.0 ch14.18 on antibody half-life by performing pharmacokinetic (PK) studies in mice injected intravenously with 5 mg/kg antibody solution. A dose escalation study was performed to determine in vivo efficacy of IgA3.0 ch14.18 in an intraperitoneal mouse model using 9464D-GD2 neuroblastoma cells as well as in a subcutaneous human xenograft model using IMR32 neuroblastoma cells. Binding assays and PK studies were compared with one-way analysis of variance (ANOVA), ADCC and ADCP assays and in vivo tumor outgrowth with two-way ANOVA followed by Tukey's post-hoc test.

RESULTS

ADCC and ADCP assays showed that particularly neutrophils and macrophages from healthy donors, non-human primates and patients with neuroblastoma are able to kill neuroblastoma tumor cells efficiently with IgA3.0 ch14.18. IgA3.0 ch14.18 contains a more favorable glycosylation pattern, corresponding to an increased antibody half-life in mice compared with IgA1 and IgA2. Furthermore, IgA3.0 ch14.18 penetrates neuroblastoma tumors in vivo and halts tumor outgrowth in both 9464D-GD2 and IMR32 long-term tumor models.

CONCLUSIONS

IgA3.0 ch14.18 is a promising new therapy for neuroblastoma, showing (1) increased half-life compared to natural IgA antibodies, (2) increased protein stability enabling effortless production and purification, (3) potent CD89-mediated tumor killing in vitro by healthy subjects and patients with neuroblastoma and (4) antitumor efficacy in long-term mouse neuroblastoma models.

Genome-wide association analyses define pathogenic signaling pathways and prioritize drug targets for IgA nephropathy

IgA nephropathy (IgAN) is a progressive form of kidney disease defined by glomerular deposition of IgA. Here we performed a genome-wide association study of 10,146 kidney-biopsy-diagnosed IgAN cases and 28,751 controls across 17 international cohorts. We defined 30 genome-wide significant risk loci explaining 11% of disease risk. A total of 16 loci were new, including TNFSF4/TNFSF18, REL, CD28, PF4V1, LY86, LYN, ANXA3, TNFSF8/TNFSF15, REEP3, ZMIZ1, OVOL1/RELA, ETS1, IGH, IRF8, TNFRSF13B and FCAR. The risk loci were enriched in gene orthologs causing abnormal IgA levels when genetically manipulated in mice. We also observed a positive genetic correlation between IgAN and serum IgA levels. High polygenic score for IgAN was associated with earlier onset of kidney failure. In a comprehensive functional annotation analysis of candidate causal genes, we observed convergence of biological candidates on a common set of inflammatory signaling pathways and cytokine ligand-receptor pairs, prioritizing potential new drug targets.

A Rare Presentation of IgA Nephropathy in a 62-Year-Old Hispanic Female

A case of immunoglobulin A (IgA) nephropathy is presented here that demonstrates an unusual clinical presentation in multiple ways and is vitally important for clinicians to consider. The patient is a Hispanic female in her 7th decade of life that presented with nephrotic-range proteinuria without hematuria ultimately leading to a diagnosis of IgA nephropathy. After diagnosis, her clinical course was complicated by continued poorly controlled type II diabetes mellitus and hypertension, and ultimately her kidney disease progressed to chronic kidney disease IV and then end-stage renal disease requiring hemodialysis. Though IgA nephropathy predominantly presents as nephritic syndrome, it can also present as nephrotic range proteinuria and even rapidly progressive glomerulonephritis which should be considered even when the patient's ethnicity and age group carry a smaller risk.

Serum sCD40L and IL-31 in Association with Early Phase of IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a major cause of chronic glomerulonephritis worldwide. T cell dysregulation has been reported to contribute to the pathogenesis of IgAN. Methods We measured a broad range of Th1, Th2 and Th17 cytokines in the serum of IgAN patients. We searched for significant cytokines, which were associated with clinical parameters and histological scores in IgAN patients.

RESULTS

Among 15 cytokines, the levels of soluble CD40L (sCD40L) and IL-31 were higher in IgAN patients and were significantly associated with a higher estimated glomerular filtration rate (eGFR), a lower urinary protein to creatinine ratio (UPCR), and milder tubulointerstitial lesions (i.e., the early phase of IgAN). Multivariate analysis revealed that serum sCD40L was an independent determinant of a lower UPCR after adjustment for age, eGFR, and mean blood pressure (MBP). CD40, a receptor of sCD40L, has been reported to be upregulated on mesangial cells in IgAN. The sCD40L/CD40 interaction may directly induce inflammation in mesangial areas and may therefore be involved in the development of IgAN.

CONCLUSIONS

The present study demonstrated the significance of serum sCD40L and IL-31 in the early phase of IgAN. Serum sCD40L may be a marker of the beginning of inflammation in IgAN.

Cost-Effectiveness Analysis of Nefecon versus Best Supportive Care for People with Immunoglobulin A Nephropathy (IgAN) in the United States

Purpose

To estimate the cost-effectiveness of Nefecon in addition to the best supportive care (BSC) vs BSC in a hypothetical cohort of commercially insured adult patients with primary immunoglobulin A nephropathy (IgAN) from a United States (US) societal perspective.

Methods

A lifetime horizon, semi-Markov model was developed that consisted of nine health states: chronic kidney disease (CKD) stage 1, 2, 3a, 3b, 4, end-stage renal disease (ESRD) with dialysis, ESRD without dialysis, post-kidney transplant, and death. Health state occupancy was estimated from individual patient-level data from the Phase 3 randomized controlled trial NefIgArd Part A (NCT03643965). Additional scenarios evaluated the impact of varying the time horizon, discounting, costs included, rounds of treatment, and the method used to calculate transition probabilities.

Results

In the deterministic base case analysis over a lifetime horizon, Nefecon plus BSC (hereafter Nefecon) had an incremental cost of $3,810 vs BSC. Nefecon resulted in a mean survival gain of 0.247 quality-adjusted life years (QALYs), 0.195 life years (LYs), and 0.244 equal value life years (evLYs) vs BSC alone - this resulted in incremental cost-effectiveness ratios (ICERs) of $15,428 per QALY, $19,502 per LY, and $15,611 per evLY gained. Probabilistic sensitivity analyses estimated that with willingness to pay thresholds of $100,000, $150,000, and $250,000 per QALY gained, Nefecon would be cost-effective over BSC in 66.70%, 75.02%, and 86.82% of cases, respectively. In the scenario analysis, Nefecon remained cost-effective with 4 rounds of treatment.

Conclusion

Nefecon was associated with LY and QALY gains vs BSC, with an incremental cost of $3,810. Based on these values, with a willingness to pay threshold of $100,000 per QALY gained, Nefecon was found to be a cost-effective treatment for US adults with primary IgAN.

The Human Virome and Its Crosslink with Glomerulonephritis and IgA Nephropathy

The prokaryotic, viral, fungal, and parasitic microbiome exists in a highly intricate connection with the human host. In addition to eukaryotic viruses, due to the existence of various host bacteria, phages are widely spread throughout the human body. However, it is now evident that some viral community states, as opposed to others, are indicative of health and might be linked to undesirable outcomes for the human host. Members of the virome may collaborate with the human host to retain mutualistic functions in preserving human health. Evolutionary theories contend that a particular microbe's ubiquitous existence may signify a successful partnership with the host. In this Review, we present a survey of the field's work on the human virome and highlight the role of viruses in health and disease and the relationship of the virobiota with immune system control. Moreover, we will analyze virus involvement in glomerulonephritis and in IgA nephropathy, theorizing the molecular mechanisms that may be responsible for the crosslink with these renal diseases.

New-onset IgA nephropathy following COVID-19 vaccination

Coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused significant economic and health damage worldwide. Rapid vaccination is one of the key strategies to curb severe illness and death due to SARS-CoV-2 infection. Hundreds of millions of people worldwide have received various COVID-19 vaccines, including mRNA vaccines, inactivated vaccines and adenovirus-vectored vaccines, but the side effects and efficacy of most vaccines have not been extensively studied. Recently, there have been increasing reports of immunoglobulin A nephropathy (IgAN) after COVID-19 vaccination, however, whether their relationship is causal or coincidental remains to be verified. Here, we summarize the latest clinical evidence of IgAN diagnosed by renal biopsy associated with the COVID-19 vaccine published by 10 July 2022 with the largest sample size, and propose a hypothesis for the pathogenesis between them. At the same time, the new opportunity presented by COVID-19 vaccine allows us to explore the mechanism of IgAN recurrence for the first time. Indeed, we recognize that large-scale COVID-19 vaccination has enormous benefits in preventing COVID-19 morbidity and mortality. The purpose of this review is to help guide the clinical assessment and management of IgA nephropathy post-COVID-19 vaccination and to enrich the 'multi-hit' theory of IgA nephropathy.

Living Donor Kidney Transplant in Recipients With Glomerulonephritis: Donor Recipient Biologic Relationship and Allograft Outcomes

Using the Scientific Registry of Transplant Recipients, we examined the association between donor-recipient biologic relationship and long-term recipient and allograft survival among glomerulonephritis (GN) patients. Four GN types were studied: membranous nephropathy, IgA, lupus-associated nephritis, and focal segmental glomerulosclerosis (FSGS). We identified all adult primary living-donor recipients between 2000 and 2018 (n = 19,668): related (n = 10,437); unrelated (n = 9,231). Kaplan-Meier curves were generated for the recipient, death-censored graft survival and death with functioning graft through ten years post-transplant. Multivariable Cox proportional hazard models were used to examine the association between the donor-recipient relationship and outcomes of interest. There was an increased risk for acute rejection by 12 months post-transplant among the unrelated compared to the related group in IgA (10.1% vs. 6.5%, p<0.001), FSGS (12.1% vs. 10%, p-0.016), and lupus nephritis (11.8% vs. 9.2%; p-0.049). The biological donor-recipient relationship was not associated with a worse recipient or graft survival or death with functioning graft in the multivariable models. These findings are consistent with the known benefits of living-related-donor kidney transplants and counter the reports of the potential adverse impact of the donor-recipient biologic relationship on allograft outcomes.

IgA Nephropathy: Pleiotropic impact of Epstein-Barr virus infection on immunopathogenesis and racial incidence of the disease

IgA nephropathy (IgAN) is an autoimmune disease in which poorly galactosylated IgA1 is the antigen recognized by naturally occurring anti-glycan antibodies, leading to formation of nephritogenic circulating immune complexes. Incidence of IgAN displays geographical and racial disparity: common in Europe, North America, Australia, and east Asia, uncommon in African Americans, many Asian and South American countries, Australian Aborigines, and rare in central Africa. In analyses of sera and cells from White IgAN patients, healthy controls, and African Americans, IgAN patients exhibited substantial enrichment for IgA-expressing B cells infected with Epstein-Barr virus (EBV), leading to enhanced production of poorly galactosylated IgA1. Disparities in incidence of IgAN may reflect a previously disregarded difference in the maturation of the IgA system as related to the timing of EBV infection. Compared with populations with higher incidences of IgAN, African Americans, African Blacks, and Australian Aborigines are more frequently infected with EBV during the first 1-2 years of life at the time of naturally occurring IgA deficiency when IgA cells are less numerous than in late childhood or adolescence. Therefore, in very young children EBV enters "non-IgA" cells. Ensuing immune responses prevent infection of IgA B cells during later exposure to EBV at older ages. Our data implicate EBV-infected cells as the source of poorly galactosylated IgA1 in circulating immune complexes and glomerular deposits in patients with IgAN. Thus, temporal differences in EBV primo-infection as related to naturally delayed maturation of the IgA system may contribute to geographic and racial variations in incidence of IgAN.

Efficacy of Traditional Chinese Medicine on Animal Model of IgA Nephropathy: A Systematic Review and Meta-Analysis

Objective

Traditional Chinese medicine (TCM) has a long history in the treatment of Immunoglobulin A nephropathy (IgAN). A large number of animal experiments focused on the TCM treatment of IgAN are conducted every year. The evidence for these preclinical studies is not clear. This study summarized and evaluated the results of animal experiments on TCM treatment for IgAN.

Methods

We systematically searched animal studies from 6 databases from inception to August 30, 2022. We included Chinese studies from the key magazine of China technology. The quality of the included studies was evaluated with the SYRCLE animal experimental bias risk assessment tool and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE).

Results

Out of 832 records identified in the initial search, 30 studies were selected. The results indicated that, compared with the control group, the TCM treatment group improved 24 h urine protein (24 h-UP) level (standardized mean difference (SMD) 3.57, 95% confidence interval (CI) 4.48 to 2.66, P < 0.001), urine red blood cell (U-RBC) (SMD 13.66, 95% CI 17.99 to 9.32, P < 0.001), serum creatinine (Scr) (mean difference (MD) 10.89, 95% CI 17.00 to 4.77, P < 0.001), blood urea nitrogen (BUN) (MD 2.44, 95% CI 3.42 to 1.47, P < 0.001), tumor necrosis factor-α (TNF-α) (MD 171.28 to 95% CI 323.68 to 18.88, P=0.03), transforming growth factor-β1 (TGF-β) (SMD 4.02, 95% CI 7.26 to 0.77, P=0.02), matrix metalloproteinase-9/tissue inhibitors of metalloproteinase-1(MMP-9/TIMP-1) (MD 0.03, 95% CI 0.00 to 0.06, P=0.02), nephrin mRNA (SMD 3.39, 95% CI 2.59 to 4.18, P < 0.001). However, there is no difference in albumin level (MD 1.10, 95% CI 0.06 to 2.26, P=0.06) and interleukin-6 (IL-6) (MD 170.77, 95% CI 365.3 to 23.75, P=0.09).

Conclusions

TCM can improve 24 h-UP, U-RBC, Scr, BUN, MMP-9/TIMP-1, TNF-α, TGF-β, and nephrin mRNA of IgAN animal models. Moreover, there is a need for rigorous reporting of preclinical research methodology, which is essential to support the quality of preclinical research. Registration. This review was registered with a systematic review record CRD42020171404 in the PROSPERO database.

IgA nephropathy pathogenesis and therapy: Review & updates

BACKGROUND

IgA nephropathy (IgAN) is the most frequent type of primary glomerulonephritis since the first type was described more than four decades ago. It is the prevalent cause of primary glomerular disease that causes end-stage renal disease. In most patients with IgAN, hematuria is the most common reported symptom, particularly in those with a preceding upper respiratory tract infection. Although the pathogenesis of IgAN is usually multifactorial, autoimmune complex formation and inflammatory processes are the most widely recognized pathogenic mechanisms. Multiple approaches have been trialed as a therapy for IgAN, including tonsillectomy, steroids, other immune-suppressive therapy in different regimens, and kidney transplantation.

AIM AND METHOD

PubMed, Google, Google Scholar, Scopus, and EMBASE were searched by the authors using different texts, keywords, and phrases. A non-systemic clinical review is intended to review the available data and clinical updates about the possible mechanism(s) of IgAN pathogenesis and treatments.

CONCLUSION

IgAN has a heterogeneous pattern worldwide, making it difficult to understand its pathogenesis and treatment. Proteinuria is the best guide to follow up on the IgAN progression and treatment response. Steroids are the cornerstone of IgAN therapy; however, other immune-suppressive and immune-modulative agents are used with a variable response rate. Kidney transplantation is highly advisable for IgAN patients, although the recurrence rate is high. Finally, IgAN management requires collaborative work between patients and their treating physicians for safe long-term outcomes.

Clinical Response to Intestine-targeted Steroid Therapy in Biopsy-proven Immunoglobulin A Nephropathy

Primary immunoglobulin A (IgA) nephropathy is associated with a dysfunctional mucosal immune system, leading to renal deposition of IgA and injury. Fifty patients with biopsy-proven IgA nephropathy were included. All patients were initiated on renin-angiotensin-aldosterone system (RAAS) inhibitors, polyunsaturated fatty acids, and a controlled release formulation (CRF) of budesonide. All drugs were started together, as isolated RAAS inhibitors will not prevent the immunological damage caused by the ongoing deposition of IgA. Depending on the histology (mesangial hypercellularity, endocapillary proliferation, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, and crescents score), the patients received 9 mg or 12 mg of budesonide. All patients were followed up every 4 weeks to monitor renal function, 24-h urinary protein, and adverse effects. Our primary outcome was a mean change in the estimated glomerular filtration rate (eGFR) and 24-h urinary protein from the baseline to the end of 6 months. The percentage of decline in mean 24-h protein at 6 months from the baseline was 33%. The mean decrease in serum creatinine from the baseline was 0.73 mg/dL. The mean gain in eGFR from the baseline was an increase of 9 mL/min/1.73 m2. Of 50 patients, 11 (22%) achieved complete remission, 20 (40%) achieved partial remission, and 16 (32%) were non-responders. Three patients (6%) were lost to follow-up. The early initiation of CRF budesonide with optimized supportive care led to reductions in proteinuria and improvements in eGFR at 6 months in patients with IgA nephropathy. Early lesions with minimal chronicity showed an excellent response to budesonide.

GABA signaling enforces intestinal germinal center B cell differentiation

Recent compelling results indicate possible links between neurotransmitters, intestinal mucosal IgA + B cell responses, and immunoglobulin A nephropathy (IgAN) pathogenesis. Here, we demonstrated that γ-amino butyric acid (GABA) transporter-2 (GAT-2) deficiency induces intestinal germinal center (GC) B cell differentiation and worsens the symptoms of IgAN in a mouse model. Mechanistically, GAT-2 deficiency enhances GC B cell differentiation through activation of GABA–mammalian target of rapamycin complex 1 (mTORC1) signaling. In addition, IgAN patients have lower GAT-2 expression but higher activation of mTORC1 in blood B cells, and both are correlated with kidney function in IgAN patients. Collectively, this study describes GABA signaling–mediated intestinal mucosal immunity as a previously unstudied pathogenesis mechanism of IgAN and challenges the current paradigms of IgAN.

The Gut and Kidney Crosstalk in Immunoglobulin A Nephropathy

Immunoglobulin A nephropathy(IgAN) is the most common primary glomerulonephritis worldwide. The working model for the pathogenesis of IgAN involves a multistep process starting from the production of galactose-deficient and polymeric immunoglobulin A-1 (gd-IgA1) that enters systemic circulation from gut-associated lymphoid tissue (GALT). Galactose-deficient IgA are targeted by endogenous IgG, leading to the formation of circulating immune complexes that deposit in the mesangium and resulting in glomerular inflammation. Disease onset and relapses are often associated with gut infections, supporting the hypothesis that the gut plays an important pathogenic role. In the presence of microbial pathogens or food antigens, activated dendritic cells in the gut mucosa induce T cell dependent and independent B cell differentiation into IgA secreting plasma cells. In IgAN patients, this promotes the systemic release of mucosal gd-IgA1. Not all bacterial strains have the same capacity to elicit IgA production, and little is known about the antigen specificity of the pathogenic gd-IgA1. However, efficacy of treatments targeting gut inflammation support a pathogenic link between the bowel immune system and IgAN. Herein, we review the evidence supporting the role of gut inflammation in IgAN pathogenesis.

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.

Increased proportion of follicular helper T cells is associated with B cell activation and disease severity in IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, characterized by glomerular deposition of IgA immune complexes, mainly produced by B cells under the regulation of CD4⁺T cells. However, the alterations of specific CD4⁺T cell subsets and the mechanism of B cells activation in IgAN remain unclear. Therefore, we aimed to investigate the landscape characteristics and role of CD4⁺T cells in the progression of IgAN. We identified that the proportion of Th2, Th17 and Tfh (follicular helper T) cells in patients with IgAN was significantly higher than that of healthy controls (P < 0.05). Single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) showed that Th cells and B cells in patients with IgAN were more activated. Correspondingly, multiplex immunohistochemistry staining of renal biopsy showed increased infiltration of CD4⁺T and B cells in the kidneys of patients with IgAN. The degree of infiltration was positively correlated with the degree of renal damage. Interestingly, the proportion of Tfh cells in peripheral blood was positively correlated with the severity of proteinuria. Moreover, the proximity position of Tfh cells and B cells suggested that cell-cell interactions between Tfh and B cells were happening in situ. Intercellular communication analysis also showed enhanced interaction between Tfh cells and B cells in IgAN. Our findings suggested that Tfh cells of patients possibly contributed to the progression of IgAN by activating B cells via cell-cell interactions and TNFSF14-TNFRSF14 may be an underlying signaling pathway.

Cytokines and Production of Aberrantly O-Glycosylated IgA1, the Main Autoantigen in IgA Nephropathy

Immunoglobulin A (IgA) nephropathy is the most common primary glomerulonephritis worldwide, with no disease-specific treatment and up to 40% of patients progressing to kidney failure. IgA nephropathy (IgAN), characterized by IgA1-containing immunodeposits in the glomeruli, is considered to be an autoimmune disease in which the kidneys are injured as innocent bystanders. Glomerular immunodeposits are thought to originate from the circulating immune complexes that contain aberrantly O-glycosylated IgA1, the main autoantigen in IgAN, bound by IgG autoantibodies. A common clinical manifestation associated with IgAN includes synpharyngitic hematuria at disease onset or during disease activity. This observation suggests a connection of disease pathogenesis with an activated mucosal immune system of the upper-respiratory and/or gastrointestinal tract and IgA1 glycosylation. In fact, some cytokines can enhance production of aberrantly O-glycosylated IgA1. This process involves abnormal cytokine signaling in IgA1-producing cells from patients with IgAN. In this article, we present our view of pathogenesis of IgAN and review how some cytokines can contribute to the disease process by enhancing production of aberrantly glycosylated IgA1. We also review current clinical trials of IgAN based on cytokine-targeting therapeutic approaches.

PPARβ/δ Augments IL-1β-Induced COX-2 Expression and PGE2 Biosynthesis in Human Mesangial Cells via the Activation of SIRT1

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ), a ligand-activated nuclear receptor, regulates lipid and glucose metabolism and inflammation. PPARβ/δ can exert an anti-inflammatory effect by suppressing proinflammatory cytokine production. Cyclooxygenase-2 (COX-2)-triggered inflammation plays a crucial role in the development of many inflammatory diseases, including glomerulonephritis. However, the effect of PPARβ/δ on the expression of COX-2 in the kidney has not been fully elucidated. The present study showed that PPARβ/δ was functionally expressed in human mesangial cells (hMCs), where its expression was increased by interleukin-1β (IL-1β) treatment concomitant with enhanced COX-2 expression and prostaglandin E2 (PGE2) biosynthesis. The treatment of hMCs with GW0742, a selective agonist of PPARβ/δ, or the overexpression of PPARβ/δ via an adenovirus-mediated approach significantly increased COX-2 expression and PGE2 production. PPARβ/δ could further augment the IL-1β-induced COX-2 expression and PGE2 production in hMCs. Moreover, both PPARβ/δ activation and overexpression markedly increased sirtuin 1 (SIRT1) expression. The inhibition or knockdown of SIRT1 significantly attenuated the effects of PPARβ/δ on the IL-1β-induced expression of COX-2 and PGE2 biosynthesis. Taken together, PPARβ/δ could augment the IL-1β-induced COX-2 expression and PGE2 production in hMCs via the SIRT1 pathway. Given the critical role of COX-2 in glomerulonephritis, PPARβ/δ may represent a novel target for the treatment of renal inflammatory diseases.

Association of HLA-DRB1 and -DQB1 Alleles with Susceptibility to IgA Nephropathy in Korean Patients

Background

Associations between IgA nephropathy (IgAN) and HLA-DRB1 and -DQB1 alleles have been reported in several ethnic groups. We investigated the association of HLA-DRB1 and -DQB1 alleles with the predisposition for IgAN and disease progression to end-stage kidney disease (ESKD) in Korean patients.

Methods

We analyzed HLA-DRB1 and -DQB1 genotypes in 399 IgAN patients between January 2000 and January 2019 using a LIFECODES sequence-specific oligonucleotide (SSO) typing kit (Immucor, Stamford, CT, USA) or a LABType SSO Typing Test (One Lambda, Canoga Park, CA, USA). Alleles with a significant difference in two-digit resolution were further analyzed using in-house sequence-based typing and sequence-specific primer PCR. As controls, 613 healthy hematopoietic stem cell donors were included. Kidney survival was analyzed in 281 IgAN patients with available clinical and laboratory data using Cox regression analysis. Where needed, P-values were adjusted using Bonferroni correction.

Results

The allele frequencies of HLA-DRB1*0405 (corrected P [Pc]<0.001), -DQB1*0401 (Pc=0.048), and -DQB1*0302 (Pc=0.021) were significantly higher in IgAN patients than in controls, whereas those of HLA-DRB1*0701, -DRB1*1501, -DQB1*0202, and -DQB1*0602 (Pc<0.001 for all) were significantly lower in IgAN patients than in controls. The allele frequency of HLA-DQB1*0503 (Pc=0.016) was significantly lower in the ESKD group than in the non-ESKD group; however, there was no significant difference for ESKD progression between these groups.

Conclusions

We report novel associations of HLA-DRB1*1501, DQB1*0202, -DQB1*0302, and -DQB1*0401 with IgAN. Further studies of HLA alleles associated with IgAN progression in a larger cohort and in various ethnic groups are needed.

Relationship between IgA Nephropathy and Porphyromonas gingivalis; Red Complex of Periodontopathic Bacterial Species

IgA nephropathy (IgAN) has been considered to have a relationship with infection in the tonsil, because IgAN patients often manifest macro hematuria just after tonsillitis. In terms of oral-area infection, the red complex of periodontal bacteria (Porphyromonas gingivalis (P. gingivalis), Treponema denticol (T. denticola) and Tannerella forsythia (T. forsythia)) is important, but the relationship between these bacteria and IgAN remains unknown. In this study, the prevalence of the red complex of periodontal bacteria in tonsil was compared between IgAN and tonsillitis patients. The pathogenicity of IgAN induced by P. gingivalis was confirmed by the mice model treated with this bacterium. The prevalence of P. gingivalis and T. forsythia in IgAN patients was significantly higher than that in tonsillitis patients (p < 0.001 and p < 0.05, respectively). A total of 92% of tonsillitis patients were free from red complex bacteria, while only 48% of IgAN patients had any of these bacteria. Nasal administration of P. gingivalis in mice caused mesangial proliferation (p < 0.05 at days 28a nd 42; p < 0.01 at days 14 and 56) and IgA deposition (p < 0.001 at day 42 and 56 after administration). Scanning-electron-microscopic observation revealed that a high-density Electron-Dense Deposit was widely distributed in the mesangial region in the mice kidneys treated with P. gingivalis. These findings suggest that P. gingivalis is involved in the pathogenesis of IgAN.

Poly-IgA Complexes and Disease Severity in IgA Nephropathy

BACKGROUND AND OBJECTIVES

Poly-IgA immune complex formation and glomerular deposition play a key role in IgA nephropathy. Our study sought to develop a new methodology for one-step serologic detection of poly-IgA levels.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A novel ELISA method using recombinant CD89 as a "capturing" probe was established for detecting poly-IgA immune complex in plasma. We applied semiquantitative measurements of these poly-IgA indices in patients recruited at Peking University First Hospital who had IgA nephropathy or other kidney disease types, as compared with healthy controls. The longitudinal trend of the poly-IgA index and the association with pathologic parameters and treatment responses were evaluated. Finally, we analyzed the molecular composition of poly-IgA complexes in patients by mass spectrometry.

RESULTS

Recombinant CD89-mounted ELISA plates specifically captured plasma poly-IgA. The levels of poly-IgA immune complex (26.7 [interquartile range (IQR) 17.1-42.6] U/ml) in IgA nephropathy were significantly higher than those in healthy controls (15.5 [IQR 10.7-20.0] U/ml; P<0.001) or in controls with non-IgA nephropathy disease (14.8 [IQR 10.5-21.9] U/ml; P<0.001). Higher levels of poly-IgA immune complex were associated with lower eGFR and worse kidney outcome. Accuracy parameters and concordant statistics showed good discrimination between IgA nephropathy and healthy controls based on poly-IgA index levels (area under the curve [AUC], 0.78; 95% confidence interval [95% CI], 0.72 to 0.83; P<0.001), significantly outperforming galactose-deficient IgA1 levels (AUC, 0.70; P=0.05). Corticosteroid and immunosuppressant treatments lowered poly-IgA indices. After a recombinant CD89-directed workflow in conjunction with mass spectrometry, we also analyzed the molecular composition of IgA immune complex in patients with IgA nephropathy.

CONCLUSIONS

Higher level of recombinant CD89-bound poly-IgA immune complex was associated with the severity of the disease and with treatment response to steroids and immunosuppressants.

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.

The influences of α-hemolytic Streptococcus on class switching and complement activation of human tonsillar cells in IgA nephropathy

While β-hemolytic streptococcus (β-HS) infections are known to predispose patients to acute poststreptococcal glomerulonephritis, there is evidence that implicates α-hemolytic streptococcus (α-HS) in IgA nephropathy (IgAN). The alternative pathway of the complement system has also been implicated in IgAN. We aimed to explore the association between α-HS and complement activation in human tonsillar mononuclear cells (TMCs) in IgAN. In our study, α-HS induced higher IgA levels than IgG levels, while β-HS increased higher IgG levels than IgA levels with more activation-induced cytidine deaminase, in TMCs in the IgAN group. Aberrant IgA1 O-glycosylation levels were higher in IgAN patients with α-HS. C3 and C3b expression was decreased in IgAN patients, but in chronic tonsillitis control patients, the expression decreased only after stimulation with β-HS. Complement factor B and H (CFH) mRNA increased, but the CFH concentration in culture supernatants decreased with α-HS. The percentage of CD19 + CD35 + cells/complement receptor 1 (CR1) decreased with α-HS more than with β-HS, while CD19 + CD21 + cells/complement receptor 2 (CR2) increased more with β-HS than with α-HS. The component nephritis-associated plasmin receptor (NAPlr) of α-HS was not detected on tonsillar or kidney tissues in IgAN patients and was positive on cultured TMCs and mesangial cells. We concluded that α-HS induced the secretion of aberrantly O-glycosylated IgA while decreasing the levels of the inhibitory factor CFH in culture supernatants and CR1 + B cells. These findings provide testable mechanisms that relate α-HS infection to abnormal mucosal responses involving the alternative complement pathway in IgAN.

Pathogenesis of IgA Nephropathy: Current Understanding and Implications for Development of Disease-Specific Treatment

IgA nephropathy, initially described in 1968 as a kidney disease with glomerular “intercapillary deposits of IgA-IgG”, has no disease-specific treatment and is a common cause of kidney failure. Clinical observations and laboratory analyses suggest that IgA nephropathy is an autoimmune disease wherein the kidneys are damaged as innocent bystanders due to deposition of IgA1-IgG immune complexes from the circulation. A multi-hit hypothesis for the pathogenesis of IgA nephropathy describes four sequential steps in disease development. Specifically, patients with IgA nephropathy have elevated circulating levels of IgA1 with some O-glycans deficient in galactose (galactose-deficient IgA1) and these IgA1 glycoforms are recognized as autoantigens by unique IgG autoantibodies, resulting in formation of circulating immune complexes, some of which deposit in glomeruli and activate mesangial cells to induce kidney injury. This proposed mechanism is supported by observations that (i) glomerular immunodeposits in patients with IgA nephropathy are enriched for galactose-deficient IgA1 glycoforms and the corresponding IgG autoantibodies; (ii) circulatory levels of galactose-deficient IgA1 and IgG autoantibodies predict disease progression; and (iii) pathogenic potential of galactose-deficient IgA1 and IgG autoantibodies was demonstrated in vivo. Thus, a better understanding of the structure–function of these immunoglobulins as autoantibodies and autoantigens will enable development of disease-specific treatments.

IgA glycosylation and immune complex formation in IgAN

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. This disease, discovered in 1968, is characterized by IgA-IgG glomerular immunodeposits with a mesangial pattern. It is thought that these immunodeposits originate from the immune complexes formed in the circulation. It is hypothesized that the pathogenesis of IgAN is driven by aberrant glycoforms of IgA1 (galactose-deficient IgA1, Gd-IgA1). Gd-IgA1, in genetically susceptible individuals, represents the initiating factor for the formation of circulating immune complexes due to its recognition by IgG autoantibodies and the subsequent formation of pathogenic IgA1-IgG immune complexes. Complement activation through alternative and/or lectin pathways is likely playing an important role in the pathogenic properties of these complexes and may further upregulate local inflammatory responses and glomerular injury.

A Systematic Literature Review of the Epidemiology, Health-Related Quality of Life Impact, and Economic Burden of Immunoglobulin A Nephropathy

Introduction: This systematic literature review analyzed published evidence on IgA nephropathy (IgAN), focusing on US epidemiology, health-related quality of life (HRQoL), and economic burden of illness. Methods: Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, Embase®, MEDLINE®, Cochrane, and Econlit (January 2010 to June 2020) were searched, along with relevant congresses (2017-2020). Results: Of 123 epidemiologic studies selected for data extraction, 24 reported IgAN diagnosis rates ranging from 6.3% to 29.7% among adult and pediatric patients undergoing renal biopsy, with all reported US rates <15%. No US studies reported IgAN prevalence. A meta-analysis of US studies calculated an annual incidence of 1.29/100 000 people, translating to an annual US incidence of 4236 adults and children. Relative to Europe, the United States had more patients diagnosed with IgAN in later chronic kidney disease stages. US rates of transition to end-stage renal disease (ESRD) ranged from 12.5% to 23% during 3-3.9 years of observation, rising to 53% during 19 years of observation. Across 8 studies reporting HRQoL, pain and fatigue were the most reported symptoms, and patients consistently ranked kidney function and mortality as the most important treatment outcomes. Patients with glomerulopathy reported worse mental health than healthy controls or hemodialysis patients; proteinuria was significantly associated with poorer HRQoL and depression. Conclusion: While economic evidence in IgAN remains sparse, management of ESRD is a major cost driver. IgAN is a rare disease where disease progression causes increasing patient burden, underscoring the need for therapies that prevent kidney function decline and HRQoL deterioration while reducing mortality.

History of IgA Nephropathy Mouse Models

IgA nephropathy (IgAN) is the most common primary glomerulonephritis in the world. It was first described in 1968 by Jean Berger and Nicole Hinglais as the presence of intercapillary deposits of IgA. Despite this simple description, patients with IgAN may present very broad clinical features ranging from the isolated presence of IgA in the mesangium without clinical or biological manifestations to rapidly progressive kidney failure. These features are associated with a variety of histological lesions, from the discrete thickening of the mesangial matrix to diffuse cell proliferation. Immunofluorescence on IgAN kidney specimens shows the isolated presence of IgA or its inconsistent association with IgG and complement components. This clinical heterogeneity of IgAN clearly echoes its complex and multifactorial pathophysiology in humans, inviting further analyses of its various aspects through the use of experimental models. Small-animal models of IgAN provide the most pertinent strategies for studying the multifactorial aspects of IgAN pathogenesis and progression. Although only primates have the IgA1 subclass, several murine models have been developed in which various aspects of immune responses are deregulated and which are useful in the understanding of IgAN physiopathology as well as in the assessment of IgAN therapeutic approaches. In this manuscript, we review all murine IgAN models developed since 1968 and discuss their remarkable contribution to understanding the disease.

Positive renal familial history in IgA nephropathy is associated with worse renal outcomes: a single-center longitudinal study

Background

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Although most IgAN cases are sporadic, few show a familial aggregation. However, the prevalence and prognosis of IgAN individuals with positive familial history (FH) of renal disorders remains uncertain. To address these issues, we conducted a longitudinal observational study on a single-institution cohort of patients with biopsy-proven IgAN.

Methods

A total of 467 IgAN patients who underwent renal biopsy during 1994 to 2019 were ascertained to have positive- or negative-FH by history taking and were followed for an average of 8.9 years. We compared the clinical and pathological features of the two subgroups. The primary outcome, a composite of a hard endpoint (end-stage renal disease [ESRD]) and surrogate endpoint (a 50% or more reduction in the estimated glomerular filtration rate [eGFR] from baseline), was evaluated. To estimate the risk for progression to ESRD, a Cox proportional hazards analysis was performed for a subset of patients who underwent follow-up for > 2 years and had an eGFR > 30 mL/min/1.73 m² at baseline (n = 389; observation, 8.7 years).

Results

Positive-FH subtype accounted for 11.6% (n = 54) of all IgAN patients. At baseline, there were no significant differences between the positive- and negative-FH subgroups regarding age, sex, comorbid disease, MEST-C score, observation period, and therapeutic interventions. However, the eGFR value at baselines was significantly lower in the positive-FH subgroup than in the negative-FH subgroup (P < 0.01). On multivariate analysis, positive-FH emerged an independent determinant of poorer renal outcomes (odds ratio, 2.31; 95% confidence interval, 1.10–4.85; P = 0.03), after adjusting for confounding factors. eGFR at follow-up was significantly lower in the positive-FH subgroup than in the negative-FH subgroup after adjustment for age and observation period.

Conclusions

Positive-FH was found in 11.6% of all IgAN patients, consistent with the incidence seen in previous literature. A significantly lower eGFR at baseline and last follow-up and unfavorable renal outcomes in the positive-FH subgroup suggest that certain genetic risk factors predisposing to renal failure may exist in a fraction of our IgAN cohort. (331 words).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02425-8.

Role of Human Mesangial-Tubular Crosstalk in Secretory IgA-Induced IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) is characterized by the mesangial deposition of pathogenic IgA. We previously detected the deposition of pathogenic secretory IgA (SIgA) in the mesangium of about one-third of IgAN patients. Tubulointerstitial injury has an important role in the development of IgAN. However, the relationship between SIgA and tubulointerstitial damage is currently unclear. In this work, the role of the mesangial-tubular crosstalk was explored in the tubulointerstitial damage in SIgA-induced IgAN.

METHODS

SIgA deposition in renal tissues of IgAN patients was detected by immunofluorescence. Flow cytometry was used to assess the binding of SIgA to human renal mesangial cells (HRMC) and human proximal tubule epithelial (HK-2) cells. HK-2 was co-cultured with HRMC added with SIgA isolated from patients or normal volunteers. Protein synthesis and gene expressions of TNF-α, TGF-β1, and MCP-1 were determined by ELISA and PCR, respectively. The expressions of the above cytokines in renal tissues of patients and normal controls were detected by immunohistochemistry.

RESULTS

Twenty-nine of 96 patients had SIgA deposition in the mesangium, but SIgA was rarely detected in the tubulointerstitium. The binding rate of SIgA to HK-2 (2.79%) was significantly lower than that of HRMC (81.6%) (p < 0.001). The expressions of TNF-α, TGF-β1, and MCP-1 in HRMC were significantly higher than in SIgA-stimulated HK-2 (p < 0.05), and their expressions were significantly higher in the SIgA-stimulated co-culture group compared with SIgA-stimulated HRMC (p < 0.05). The expressions of the above cytokines were mainly detected in tubulointerstitium of IgAN patients with positive and negative SIgA deposition, without significant difference between the 2 groups, but to a significantly higher level than that in normal controls, and their expressions positively correlated with tubulointerstitial injury.

CONCLUSION

Inflammatory factors released from the mesangium after SIgA deposition might mediate tubulointerstitial damage via mesangial-tubular crosstalk in IgAN.

A Partial Picture of the Single-Cell Transcriptomics of Human IgA Nephropathy

The molecular mechanisms underlying renal damage of IgA nephropathy (IgAN) remain incompletely defined. Here, single-cell RNA sequencing (scRNA-seq) was applied to kidney biopsies from IgAN and control subjects to define the transcriptomic landscape at single-cell resolution. We presented a comprehensive scRNA-seq analysis of human renal biopsies from IgAN. We showed for the first time that IgAN mesangial cells displayed increased expression of several novel genes including MALAT1, GADD45B, SOX4, and EDIL3, which were related to cell proliferation and matrix accumulation. The overexpressed genes in tubule cells of IgAN were mainly enriched in inflammatory pathways including TNF signaling, IL-17 signaling, and NOD-like receptor signaling. Furthermore, we compared the results of 4 IgAN patients with the published scRNA-Seq data of healthy kidney tissues of three human donors in order to further validate the findings in our study. The results also verified that the overexpressed genes in tubule cells from IgAN patients were mainly enriched in inflammatory pathways including TNF signaling, IL-17 signaling, and NOD-like receptor signaling. The receptor-ligand crosstalk analysis revealed potential interactions between mesangial cells and other cells in IgAN. IgAN patients with overt proteinuria displayed elevated genes participating in several signaling pathways compared with microproteinuria group. It needs to be mentioned that based on number of mesangial cells and other kidney cells analyzed in this study, the results of our study are preliminary and needs to be confirmed on larger number of cells from larger number of patients and controls in future studies. Therefore, these results offer new insight into pathogenesis and identify new therapeutic targets for IgAN.

B cell and monocyte phenotyping: A quick asset to investigate the immune status in patients with IgA nephropathy

Background

IgA nephropathy (IgAN) advances from multiple pathogenic “hits” resulting in poorly O-galactosylated IgA1 glycoforms (Gd-IgA1), production of antibodies and glomerular deposition of immune complexes. A sequence of immune responses arising from plasma cells, T cells and antigen presenting cells (APCs), causes glomerular injury. This study was designed to phenotype subsets of B cells, monocytes and T cells in the peripheral circulation and their association with inflammatory cytokines and kidney function in patients with IgAN, healthy controls (HC) and disease controls with autosomal dominant polycystic kidney disease (ADPKD).

Methods

Patients with IgAN (n = 13), median estimated glomerular filtration rate (eGFR) of 57 ml/min/1.73m² (IQR 42–84), patients with ADPKD (n = 13) matched for kidney function, gender and age and gender and age-matched HC (n = 13) were recruited. CD3+ and CD3- peripheral blood mononuclear cells were isolated and profiled based on their specific surface markers for different subsets of monocytes, B and T cells and analyzed by flow cytometry. Cytokines were analyzed by ELISA.

Results

We observed a significant decrease in the proportion of pre-switched B cells and plasmablasts, but an increase in long-lived plasma cells in the peripheral circulation of IgAN patients compared to HC. The proportion of non-classical monocytes was significantly higher in IgAN patients compared to both HC and ADPKD. We also report an association between sCD40L levels and the proportion of pre-switched B cells, as well as sCD40L and MCP-1 levels and albuminuria in IgAN patients.

Conclusions

We applied an easy-access method to analyze subsets of immune cells as well as relevant inflammatory mediators in IgAN patients. Our data demonstrate an altered B cell profile that indicates a pathophysiological role of the B cell lineage and an increased proportion of non-classical monocytes that suggests their role in the disease process.

Aberrant mucosal immunoreaction to tonsillar microbiota in immunoglobulin A nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis worldwide, characterized by mesangial polymeric IgA1 deposition. IgAN is believed to develop owing to aberrant mucosal immunoreaction against commensals in the tonsils. However, the exact interrelation between pathogenic IgA and mucosal microbiota in IgAN patients is unclear.

METHODS

Biopsy-proven IgAN or recurrent tonsillitis (RT) patients who had undergone tonsillectomy were enrolled. We used 16S ribosomal RNA gene amplicon sequencing with a flow cytometry-based bacterial cell sorting technique) and immunoglobulin repertoire sequencing of the IgA heavy chain to characterize IgA-coated bacteria of the tonsillar microbiota (IgA-SEQ) and their corresponding IgA repertoire. Furthermore, we fractionated patient serum using gel-filtration chromatography and performed flow cytometry-based analysis of IgA binding to bacteria cultured from incised tonsils.

RESULTS

Tonsillar proliferation-inducing ligand and B-cell activating factor levels were significantly higher in IgAN than in RT patients. IgA-SEQ for tonsillar microbiota revealed the preferential binding ability of IgA to Bacteroidetes in IgAN tonsils compared with those from RT patients. Expression of immunoglobulin heavy (IGH) constant alpha 1 with IGH variable 3-30 was significantly higher in IgAN than that in RT, and positively correlated with the IgA-coated enrichment score of Bacteroidetes. Serum polymeric IgA, comprising high levels of GdIgA1, exhibited considerable binding to Bacteroidetes strains cultured from the tonsils of IgAN patients.

CONCLUSIONS

These findings provide evidence that aberrant mucosal immune responses to tonsillar anaerobic microbiota, primarily consisting of members of the phylum Bacteroidetes, are involved in IgAN pathophysiology.

Total Nephron Number and Single-Nephron Parameters in Patients with IgA Nephropathy

Background

Single-nephron dynamics in progressive IgA nephropathy (IgAN) have not been studied. We applied novel methodology to explore single-nephron parameters in IgAN.

Methods

Nonglobally sclerotic glomeruli (NSG) and globally sclerotic glomeruli (GSG) per kidney were estimated using cortical volume assessment via unenhanced computed tomography and biopsy-based stereology. Estimated single-nephron GFR (eSNGFR) and single-nephron urine protein excretion (SNUPE) were calculated by dividing eGFR and UPE by the number of NSG. Associations with CKD stage and clinicopathologic findings were cross-sectionally investigated.

Results

This study included 245 patients with IgAN (mean age 43 years, 62% male, 45% on renin-angiotensin aldosterone system [RAAS] inhibitors prebiopsy) evaluated at kidney biopsy. CKD stages were 10% CKD1, 43% CKD2, 19% CKD3a, 14% CKD3b, and 14% CKD4-5. With advancing CKD stage, NSG decreased from mean 992,000 to 300,000 per kidney, whereas GSG increased from median 64,000 to 202,000 per kidney. In multivariable models, advancing CKD stage associated with lower numbers of NSG, higher numbers of GSG, and lower numbers of GSG + NSG, indicating potential resorption of sclerosed glomeruli. In contrast to the higher mean glomerular volume and markedly elevated SNUPE in advanced CKD, the eSNGFR was largely unaffected by CKD stage. Lower SNGFR associated with Oxford scores for endocapillary hypercellularity and crescents, whereas higher SNUPE associated with segmental glomerulosclerosis and tubulointerstitial scarring.

Conclusions

SNUPE emerged as a sensitive biomarker of advancing IgAN. The failure of eSNGFR to increase in response to reduced number of functioning nephrons suggests limited capacity for compensatory hyperfiltration by diseased glomeruli with intrinsic lesions.

GWAS-Based Discoveries in IgA Nephropathy, Membranous Nephropathy, and Steroid-Sensitive Nephrotic Syndrome

Over the past decade, genome-wide association studies (GWAS) have emerged as a powerful tool to understand the genetic basis of complex traits in humans. The GWAS approach has been successfully applied to primary glomerular disorders, providing numerous novel insights into the genetic architecture of IgA nephropathy, membranous nephropathy, and steroid-sensitive nephrotic syndrome. IgA nephropathy appears to have a highly complex polygenic architecture, with nearly 20 genome-wide significant loci of small-to-moderate effects discovered to date. In contrast, the genetic susceptibility to membranous nephropathy and steroid-sensitive nephrotic syndrome appears to be driven by a small number of large-effect loci. The MHC locus on chromosome 6p21 is strongly associated with genetic susceptibility to all major types of immune-mediated glomerulopathies. However, a distinct set of classical HLA alleles is associated with each individual disease type, pinpointing to specific immune mechanisms underlying each of these conditions. Additional insights from the discovery of non-HLA risk loci reinforced the role of innate and adaptive immunity in the pathogenesis of these disorders, and highlighted important susceptibility overlaps between glomerular and other autoimmune and inflammatory conditions. Despite these initial successes, much larger GWAS and sequencing studies are still needed for each individual glomerular disease type. Increased power will be critical to comprehensively test for genetic effects across the full spectrum of allelic frequencies, to detect gene-gene and gene-environment interactions, and to potentially improve the performance of polygenic risk predictors. Moreover, the existing studies are limited mostly to European and East Asian populations, stressing the urgency to expand genetic discovery efforts to more diverse populations worldwide.