IgA nephropathy: molecular mechanisms of the disease

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.).

Immunosuppression versus Supportive Care on Kidney Outcomes in IgA Nephropathy in the Real-World Setting

BACKGROUND

The efficacy of immunosuppression in the management of immunoglobulin A (IgA) nephropathy remains highly controversial. The study was conducted to assess the effect of immunosuppression, compared with supportive care, in the real-world setting of IgA nephropathy.

METHODS

A cohort of 3946 patients with IgA nephropathy, including 1973 new users of immunosuppressive agents and 1973 propensity score-matched recipients of supportive care, in a nationwide register data from January 2019 to May 2022 in China was analyzed. The primary outcome was a composite of 40% eGFR decrease of the baseline, kidney failure, and all-cause mortality. A Cox proportional hazard model was used to estimate the effects of immunosuppression on the composite outcomes and its components in the propensity score-matched cohort.

RESULTS

Among 3946 individuals (mean [SD] age 36 [10] years, mean [SD] eGFR 85 [28] ml/min per 1.73 m 2 , and mean [SD] proteinuria 1.4 [1.7] g/24 hours), 396 primary composite outcome events were observed, of which 156 (8%) were in the immunosuppression group and 240 (12%) in the supportive care group. Compared with supportive care, immunosuppression treatment was associated with 40% lower risk of the primary outcome events (adjusted hazard ratio, 0.60; 95% confidence interval, 0.48 to 0.75). Comparable effect size was observed for glucocorticoid monotherapy and mycophenolate mofetil alone. In the prespecified subgroup analysis, the treatment effects of immunosuppression were consistent across ages, sexes, levels of proteinuria, and values of eGFR at baseline. Serious adverse events were more frequent in the immunosuppression group compared with the supportive care group.

CONCLUSIONS

Immunosuppressive therapy, compared with supportive care, was associated with a 40% lower risk of clinically important kidney outcomes in patients with IgA nephropathy.

TFRC-RNA interactions show the regulation of gene expression and alternative splicing associated with IgAN in human renal tubule mesangial cells

Introduction: IgA nephropathy (IgAN) is the most common primary glomerular disease (PGD) which could progress to renal failure and is characterized by aberrant IgA immune complex deposition. Transferrin receptor1 (TFRC), an IgA receptor, is a potential RNA binding protein (RBP) which regulates expression of genes positively associated with the cell cycle and proliferation and is involved in IgAN. Molecular mechanisms by which TFRC affects IgAN development remain unclear. Methods: In this study, TFRC was overexpressed in human renal tubular mesangial cells (HRMCs) and RNA-sequencing (RNA-seq) and improved RNA immunoprecipitation sequencing (iRIP-seq) were performed. The aim was to identify potential RNA targets of TFRC at transcriptional and alternative splicing (AS) levels. Results: TFRC-regulated AS genes were enriched in mRNA splicing and DNA repair, consistent with global changes due to TFRC overexpression (TFRC-OE). Expression of TFRC-regulated genes potentially associated with IgAN, including CENPH, FOXM1, KIFC1, TOP2A, FABP4, ID1, KIF20A, ATF3, H19, IRF7, and H1-2, and with AS, CYGB, MCM7 and HNRNPH1, were investigated by RT-qPCR and iRIP-seq data analyzed to identify TFRC-bound RNA targets. RCC1 and RPPH1 were found to be TFRC-bound RNA targets involved in cell proliferation. Discussion: In conclusion, molecular TFRC targets were identified in HRMCs and TFRC found to regulate gene transcription and AS. TFRC is considered to have potential as a clinical therapeutic target.

Comparison between hydroxychloroquine and systemic corticosteroids in IgA nephropathy: a two-year follow-up study

BACKGROUND

Hydroxychloroquine (HCQ) is recommended as a treatment for IgA nephropathy (IgAN) to control proteinuria. The long-term effects of HCQ compared to systemic corticosteroid therapy remain unclear.

METHODS

We conducted a retrospective case‒control study at Peking University First Hospital. Thirty-nine patients with IgAN who received HCQ for at least 24 months without corticosteroids (CSs) or other immunosuppressive agents were included. Thirty-nine matched patients who received systemic CS therapy were selected using propensity score matching. Clinical data over a 24-month period were compared.

RESULTS

In the HCQ group, the level of proteinuria decreased from 1.72 [1.44, 2.35] to 0.97 [0.51, 1.37] g/d (-50.5 [-74.0, -3.4] %, P < 0.001) at 24 months. A significant decline in proteinuria was also found in the CS group, but no significant differences were found between the HCQ group and CS group in the levels of proteinuria (0.97 [0.51, 1.37] vs. 0.53 [0.25, 1.81] g/d, P = 0.707) and change rates (-50.5% [-74.0%, -3.4%] vs. -63.7% [-78.5%, -24.2%], P = 0.385) at 24 months. In addition, the decline rates of eGFR between the HCQ and CS groups were comparable (-7.9% [-16.1%, 5.8%] vs. -6.6% [-14.9%, 5.3%], P = 0.758). More adverse events were observed in the CS group.

CONCLUSIONS

Long-term use of HCQ can maintain stable renal function with minimal side effects. In patients who cannot tolerate corticosteroids, HCQ might be an effective and safe supportive therapy for IgAN.

GalNAc-T14 may Contribute to Production of Galactose-Deficient Immunoglobulin A1, the Main Autoantigen in IgA Nephropathy

Introduction

Immunoglobulin A1 (IgA1) with galactose-deficient O-glycans (Gd-IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). Mucosal-tissue infections increase IL-6 production and, in patients with IgAN, are often associated with macroscopic hematuria. IgA1-secreting cell lines derived from the circulation of patients with IgAN, compared to those of healthy controls (HCs), produce more IgA1 that has O-glycans with terminal or sialylated N-acetylgalactosamine (GalNAc). GalNAc residues are added to IgA1 hinge region by some of the 20 GalNAc transferases, the O-glycosylation-initiating enzymes. Expression of GALNT2, encoding GalNAc-T2, the main enzyme initiating IgA1 O-glycosylation, is similar in cells derived from patients with IgAN and HCs. In this report, we extend our observations of GALNT14 overexpression in IgA1-producing cell lines from patients with IgAN.

Methods

GALNT14 expression was analyzed in peripheral blood mononuclear cells (PBMCs) from patients with IgAN and from HCs. Moreover, the effect of GALNT14 overexpression or knock-down on Gd-IgA1 production in Dakiki cells was assessed.

Results

GALNT14 was overexpressed in PBMCs from patients with IgAN. IL-6 increased GALNT14 expression in PBMCs from patients with IgAN and HCs. We used IgA1-producing cell line Dakiki, a previously reported model of Gd-IgA1-producing cells, and showed that overexpression of GalNAc-T14 enhanced galactose deficiency of IgA1, whereas siRNA-mediated GalNAc-T14 knock-down reduced it. GalNAc-T14 was localized in trans-Golgi network, as expected.

Conclusions

Overexpression of GALNT14 due to inflammatory signals during mucosal infections may contribute to overproduction of Gd-IgA1 in patients with IgAN.

Long noncoding RNA FGD5-AS1 alleviates childhood IgA nephropathy by targeting PTEN-mediated JNK/c-Jun signaling pathway via miR-196b-5p

This paper studied lncRNA FGD5 antisense RNA 1 (FGD5-AS1)-associated mechanisms in immunoglobulin A nephropathy (IgAN). FGD5-AS1, miR-196b-5p, and PTEN in the serum of children with IgAN were assessed. MES-13 cells were stimulated by p-IgA1 to construct an in vitro model of IgAN. After plasmid intervention, cell proliferation, cell cycle, apoptosis, and inflammatory response were correspondingly evaluated. An IgAN mouse model was established to define FGD5-AS1/miR-196b-5p/PTEN axis-mediated alternations of 24-h proteinuria, blood urea nitrogen, serum creatinine, glomerular IgA deposition, renal fibrosis, and glycogen content in renal tissue. The changes in JNK/c-Jun pathway activation in the cell model were also tested. Our results discovered that FGD5-AS1 and PTEN were down-regulated and miR-196b-5p was up-regulated in children with IgAN. Overexpression of FGD5-AS1 or silencing of miR-196b-5p impeded the proliferation and inflammatory response and induced apoptosis of p-IgA1-stimulated MES-13 cells, and improved pathological conditions in IgAN mice. Inhibition of PTEN rescued the therapeutic effects of overexpression of FGD5-AS1 or inhibition of miR-196b-5p on IgAN. FGD5-AS1/miR-196b-5p/PTEN axis inhibited the activation of the JNK/c-Jun pathway. Taken together, FGD5-AS1 attenuates IgAN by targeting PTEN-mediated JNK/c-Jun signaling via miR-196b-5p. Therefore, FGD5-AS1 may be a new therapeutic target for IgAN.

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.

Anomalous kinetics of galactose-deficient IgA incurring nephropathy revealed by cross-scale optical imaging

IgA nephropathy (IgAN) is the most common glomerulonephritis, characterized by the presence of predominant IgA deposits in the mesangium. Deposition of pathogenic IgA in kidney tissue is a fundamental initiating process that has not been fully studied. Here, we employed optical imaging to directly visualize kidney deposition of IgA with optimized spatial and temporal resolution in BALB/c nude mice. Real-time fluorescence imaging revealed that IgA isolated from patients with IgAN preferentially accumulated in the kidneys, compared with IgA purified from healthy individuals. There was no difference in the distribution of either IgA preparation by the liver. Photoacoustic computed tomography dynamically demonstrated and quantified the enhanced retention of pathological IgA in the kidney cortex. Photoacoustic microscopy tracked IgA deposition in the glomeruli with a resolution down to three microns in a mouse model. Notably, longitudinal fluorescent imaging revealed that galactose-deficient IgA (Gd-IgA), which was elevated in the circulation of patients with IgAN, persisted in the kidney for longer than two weeks, and stable deposition of Gd-IgA induced kidney impairment, including albuminuria and mesangial proliferation. Thus, our study highlights that the aberrant kidney depositional kinetics of Gd-IgA is involved in the pathogenesis of IgAN. Hence, cross-scale optical imaging has potential applications in assessing immune-mediated kidney diseases and uncovering underlying mechanisms of disease.

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.

IL-6 and its role in IgA nephropathy development

IL-6 is considered one of the well characterized cytokines exhibiting homeostatic, pro- and anti-inflammatory activities, depending on the receptor variant and the induced intracellular cis- or trans-signaling responses. IL-6-activated pathways are involved in the regulation of cell proliferation, survival, differentiation, and cell metabolism changes. Deviations in IL-6 levels or abnormal response to IL-6 signaling are associated with several autoimmune diseases including IgA nephropathy (IgAN), one of most frequent primary glomerulonephritis worldwide. IgAN is associated with increased plasma concentration of IL-6 and increased plasma concentration of aberrantly galactosylated IgA1 immunoglobulin (Gd-IgA1). Gd-IgA1 is specifically recognized by autoantibodies, leading to the formation of circulating immune complexes (CIC) with nephritogenic potential, since CIC deposited in the glomerular mesangium induce mesangial cells proliferation and glomerular injury. Infection of the upper respiratory or digestive tract enhances IL-6 production and in IgAN patients is often followed by the macroscopic hematuria. This review recapitulates general aspects of IL-6 signaling and summarizes experimental evidences about IL-6 involvement in the etiopathogenesis of IgA nephropathy through the production of Gd-IgA1 and regulation of mesangial cell proliferation.

Triptolide promotes autophagy to inhibit mesangial cell proliferation in IgA nephropathy via the CARD9/p38 MAPK pathway

Background

Mesangial cell proliferation is the most basic pathological feature of immunoglobulin A nephropathy (IgAN); however, the specific underlying mechanism and an appropriate therapeutic strategy are yet to be unearthed. This study aimed to investigate the therapeutic effect of triptolide (TP) on IgAN and the mechanism by which TP regulates autophagy and proliferation of mesangial cells through the CARD9/p38 MAPK pathway.

Methods

We established a TP‐treated IgAN mouse model and produced IgA1‐induced human mesangial cells (HMC) and divided them into control, TP, IgAN, and IgAN+TP groups. The levels of mesangial cell proliferation (PCNA, cyclin D1, cell viability, and cell cycle) and autophagy (P62, LC3 II, and autophagy flux rate) were measured, with the autophagy inhibitor 3‐Methyladenine used to explore the relationship between autophagy and proliferation. We observed CARD9 expression in renal biopsies from patients and analyzed its clinical significance. CARD9 siRNA and overexpression plasmids were constructed to investigate the changes in mesangial cell proliferation and autophagy as well as the expression of CARD9 and p‐p38 MAPK/p38 MAPK following TP treatment.

Results

Administering TP was safe and effectively alleviated mesangial cell proliferation in IgAN mice. Moreover, TP inhibited IgA1‐induced HMC proliferation by promoting autophagy. The high expression of CARD9 in IgAN patients was positively correlated with the severity of HMC proliferation. CARD9/p38 MAPK was involved in the regulation of HMC autophagy and proliferation, and TP promoted autophagy to inhibit HMC proliferation by downregulating the CARD9/p38 MAPK pathway in IgAN.

Conclusion

TP promotes autophagy to inhibit mesangial cell proliferation in IgAN via the CARD9/p38 MAPK pathway.

Novel insights into NOD-like receptors in renal diseases

Nucleotide-binding oligomerization domain-like receptors (NLRs), including NLRAs, NLRBs (also known as NAIPs), NLRCs, and NLRPs, are a major subfamily of pattern recognition receptors (PRRs). Owing to a recent surge in research, NLRs have gained considerable attention due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, which is a central phenomenon in the pathogenesis of multiple diseases, including renal diseases. NLRs are expressed in different renal tissues during pathological conditions, which suggest that these receptors play roles in acute kidney injury, obstructive nephropathy, diabetic nephropathy, IgA nephropathy, lupus nephritis, crystal nephropathy, uric acid nephropathy, and renal cell carcinoma, among others. This review summarises recent progress on the functions of NLRs and their mechanisms in the pathophysiological processes of different types of renal diseases to help us better understand the role of NLRs in the kidney and provide a theoretical basis for NLR-targeted therapy for renal diseases.

Is There a Role for Gut Microbiome Dysbiosis in IgA Nephropathy?

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis and one of the leading causes of renal failure worldwide. The pathophysiology of IgAN involves nephrotoxic IgA1-immune complexes. These complexes are formed by galactose-deficient (Gd) IgA1 with autoantibodies against the hinge region of Gd-IgA1 as well as soluble CD89, an immune complex amplifier with an affinity for mesangial cells. These multiple molecular interactions result in the induction of the mesangial IgA receptor, CD71, injuring the kidney and causing disease. This review features recent immunological and microbiome studies that bring new microbiota-dependent mechanisms developing the disease based on data from IgAN patients and a humanized mouse model of IgAN. Dysbiosis of the microbiota in IgAN patients is also discussed in detail. Highlights of this review underscore that nephrotoxic IgA1 in the humanized mice originates from mucosal surfaces. Fecal microbiota transplantation (FMT) experiments in mice using stools from patients reveal a possible microbiota dysbiosis in IgAN with the capacity to induce progression of the disease whereas FMT from healthy hosts has beneficial effects in mice. The continual growth of knowledge in IgAN patients and models can lead to the development of new therapeutic strategies targeting the microbiota to treat this disease.

Chimeric Fusion between Clostridium ramosum IgA Protease and IgG Fc Provides Long-lasting Clearance of IgA deposits in Mouse Models of IgA Nephropathy

BACKGROUND

IgA nephropathy is a common primary glomerulonephritis caused by mesangial deposition of poly-IgA complexes. The disease follows a variable course of clinical progression with a high risk of kidney failure. While no specific therapy is available, enzymatic strategies to clear IgA deposits are being considered for the treatment of rapidly progressive IgA nephropathy.

METHODS

We chose an IgA protease of commensal bacterium Clostridium ramosum, termed AK183, as the template for constructing a recombinant biologic. To extend the half-life in blood, we fused AK183 to the Fc segment of human IgG1. Activities of this Fc-AK183 fusion protein towards the cleavage and subsequent clearance of IgA were tested in mouse models.

RESULTS

First, we discovered an autocleavage activity of AK183 that separates the N-terminal protease from its C-terminal autotransporter β domain. Therefore, we grafted Fc to the N-terminus of AK183 and demonstrated its week-long enzymatic activity in mice. In addition, the proteolytic fragments of IgA generated in the reaction with Fc-AK183 were effectively removed from circulation via kidney filtration. The combined actions of Fc-AK183-mediated cleavage and subsequent renal clearance of IgA resulted in a lasting obliteration of blood IgA, as demonstrated in a human IgA-injection model and in a humanized α1KI transgenic model. Fc-AK183 was also able to remove chronic IgA and associated complement C3 deposits in the glomerulus.

CONCLUSION

We constructed a chimeric fusion of IgA protease with Fc and demonstrated its long-lasting efficacy as a promising targeted therapy for IgA nephropathy.

Galactose-Deficient IgA1 B cells in the Circulation of IgA Nephropathy Patients Carry Preferentially Lambda Light Chains and Mucosal Homing Receptors

Background: Immunoglobulin A nephropathy (IgAN) primary glomerulonephritis is characterized by the deposition of circulating immune complexes (CIC) composed of polymeric (p)IgA1 molecules with altered O-glycans (Gd-IgA1) and anti-glycan antibodies in the kidney mesangium. The mesangial IgA deposits and serum IgA1 contain predominantly lambda (λ) light (L) chain, but the nature and origin of such IgA remains enigmatic Methods: We analyzed λ L chain expression in peripheral blood B cells of 30 IgAN patients, 30 healthy controls (HC), and 18 membranous nephropathy patients selected as disease controls (Non-IgAN). Results: In comparison to HC and Non-IgAN, in peripheral blood surface/membrane bound (mb)-Gd-IgA1⁺ cells from IgAN patients express predominantly λ L chain. In contrast, total mb-IgA⁺, mb-IgG⁺, and mb-IgM⁺ cells were preferentially positive for kappa (κ) L chain, in all analyzed groups. Although minor in comparison to κ L chain, λ L chain subsets of mb-IgG⁺, mb-IgM,⁺ and mb-IgA⁺ cells were significantly enriched in IgAN in comparison to Non-IgAN and/or HC. In contrast to HC, the peripheral blood of IgAN patients was enriched for λ⁺ mb-Gd-IgA1,⁺ CCR10,⁺ and CCR9⁺ cells, which preferentially home to the upper respiratory and digestive tract, respectively. Furthermore, we observed that mb-Gd-IgA1⁺ cell populations comprise more CD138⁺ cells and plasmablasts (CD38⁺) in comparison to total mb-IgA⁺ cells. Conclusions: Peripheral blood of IgAN patients is enriched for migratory λ⁺ mb-GdIgA1⁺ B cells, with the potential to home to mucosal sites where Gd-IgA1 could be produced during local respiratory or digestive tract infections.

Intensity of Macrophage Infiltration in Glomeruli Predicts Response to Immunosuppressive Therapy in Patients with IgA Nephropathy

BACKGROUND

The lack of a tool for predicting the response to immunosuppressive therapy in IgA nephropathy (IgAN) limits patient-specific risk stratification and early treatment decision making. Models for predicting response to immunosuppression in IgAN that can be applied at the time of kidney biopsy are needed.

METHODS

This prospective cohort study involved 621 Chinese patients with IgAN who were at high risk for disease progression and had persistent proteinuria ≥1 g/d, despite 3 months of optimized supportive care with renin-angiotensin system inhibitors. Participants received immunosuppressive therapy for a median of 18 months. We used immunochemistry to identify macrophage and lymphocyte infiltrates in biopsy specimens and digital image analysis to quantify them. The outcome was response to immunosuppression, defined as complete or partial remission within 12 months of immunosuppression.

RESULTS

Kidney infiltration of CD68 + and CD206 + macrophages increased in patients with IgAN. Having higher levels of glomerular CD206 + macrophage infiltration was associated with a 40-fold increased probability of response to immunosuppression in adjusted analysis compared with having lower levels. Patients with a higher intensity of glomerular CD68 + infiltrates had a 13-fold increase in probability of responding to immunosuppression. Intensity of glomerular CD206 + and CD68 + macrophage infiltration predicted the response to immunosuppression (area under the curve [AUC], 0.84; 95% CI, 0.81 to 0.88). The AUC increased to 0.87 (95% CI, 0.84 to 0.91) in a model combining the infiltration score of CD206 + and CD68 + infiltrates with the MEST-C score and clinical data at biopsy.

CONCLUSIONS

Intensity of glomerular macrophage infiltration predicted response to immunosuppressive therapy in patients with IgAN who were at high risk of progression, and may help physicians identify patients who will benefit from such treatment.

Propensity of IgA to self-aggregate via tailpiece cysteine-471 and treatment of IgA nephropathy using cysteamine

IgA nephropathy is caused by deposition of circulatory IgA1 in the kidney. Hypogalactosylated IgA1 has the propensity to form poly-IgA aggregates that are prone to deposition. Herein, we purified poly-IgA from the plasma of patients with IgA nephropathy and showed that the complex is susceptible to reducing conditions, suggesting intermolecular disulfide connections between IgA units. We sought to find the cysteine residue(s) that form intermolecular disulfide. Naturally assembled dimeric IgA, also known as secretory IgA, involves a J chain subunit connected with 2 IgA1 molecules via their penultimate cysteine-471 residue on a “tailpiece” segment of IgA heavy chain. It is plausible that, with the absence of J chain, the cysteine residue of mono-IgA1 might aberrantly form a disulfide bond in poly-IgA formation. Mutagenesis confirmed that cysteine-471 is capable of promoting IgA aggregation. These discoveries prompted us to test thiol-based drugs for stabilizing cysteine. Specifically, the cystine-reducing drug cysteamine used for treatment of cystinosis showed a remarkable potency in preventing self-aggregation of IgA. When administrated to rat and mouse models of IgA nephropathy, cysteamine significantly reduced glomerular IgA deposition. Collectively, our results reveal a potentially novel molecular mechanism for aberrant formation of IgA aggregates, to which the repurposed cystinosis drug cysteamine was efficacious in preventing renal IgA deposition.

Cosmc deficiency causes spontaneous autoimmunity by breaking B cell tolerance

Factors regulating the induction and development of B cell–mediated autoimmunity are not well understood. Here, we report that targeted deletion in murine B cells of X-linked Cosmc, encoding the chaperone required for expression of core 1 O-glycans, causes the spontaneous development of autoimmune pathologies due to a breakdown of B cell tolerance. BC-CosmcKO mice display multiple phenotypic abnormalities, including severe weight loss, ocular manifestations, lymphadenopathy, and increased female-associated mortality. Disruption of B cell tolerance in BC-CosmcKO mice is manifested as elevated self-reactive IgM and IgG autoantibodies. Cosmc-deficient B cells exhibit enhanced basal activation and responsiveness to stimuli. There is also an elevated frequency of spontaneous germinal center B cells in BC-CosmcKO mice. Mechanistically, loss of Cosmc confers enhanced B cell receptor (BCR) signaling through diminished BCR internalization. The results demonstrate that Cosmc, through control of core 1 O-glycans, is a previously unidentified immune checkpoint gene in maintaining B cell tolerance.

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.

Aberrantly Glycosylated IgA1 in IgA Nephropathy: What We Know and What We Don't Know

IgA nephropathy (IgAN), the most common primary glomerular disease worldwide, is characterized by glomerular deposition of IgA1-containing immune complexes. The IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine usually with β1,3-linked galactose and variable sialylation. Circulating levels of IgA1 with abnormally O-glycosylated HR, termed galactose-deficient IgA1 (Gd-IgA1), are increased in patients with IgAN. Current evidence suggests that IgAN is induced by multiple sequential pathogenic steps, and production of aberrantly glycosylated IgA1 is considered the initial step. Thus, the mechanisms of biosynthesis of aberrantly glycosylated IgA1 and the involvement of aberrant glycoforms of IgA1 in disease development have been studied. Furthermore, Gd-IgA1 represents an attractive biomarker for IgAN, and its clinical significance is still being evaluated. To elucidate the pathogenesis of IgAN, it is important to deconvolute the biosynthetic origins of Gd-IgA1 and characterize the pathogenic IgA1 HR O-glycoform(s), including the glycan structures and their sites of attachment. These efforts will likely lead to development of new biomarkers. Here, we review the IgA1 HR O-glycosylation in general and the role of aberrantly glycosylated IgA1 in the pathogenesis of IgAN in particular.

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.

Fantastic IgA plasma cells and where to find them

IgA is produced in large quantities at mucosal surfaces by IgA⁺ plasma cells (PC), protecting the host from pathogens, and restricting commensal access to the subepithelium. It is becoming increasingly appreciated that IgA⁺ PC are not constrained to mucosal barrier sites. Rather, IgA⁺ PC may leave these sites where they provide both host defense and immunoregulatory function. In this review, we will outline how IgA⁺ PC are generated within the mucosae and how they subsequently migrate to their "classical" effector site, the gut lamina propria. From there we provide examples of IgA⁺ PC displacement from the gut to other parts of the body, referencing examples during homeostasis and inflammation. Lastly, we will speculate on mechanisms of IgA⁺ PC displacement to other tissues. Our aim is to provide a new perspective on how IgA⁺ PC are truly fantastic beasts of the immune system and identify new places to find them.

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.

Renal deposition and clearance of recombinant poly-IgA complexes in a model of IgA nephropathy

IgA nephropathy (IgAN) is the most common type of glomerulonephritis worldwide, which follows a chronic but nonetheless highly variable course of progression. IgA immune complexes are the primary source of renal deposits in IgAN. Apart from the presence of granular IgA1 deposits in the glomerular mesangium and mesangial hypercellularity as common features, the detailed process of IgA1 deposition and clearance in the kidney remains unclear. We sought to examine the dynamics of IgA deposition and tissue plasticity in response to deposits including their intrarenal clearance. We followed a synthetic approach to produce a recombinant fusion between IgA Fc (rIgA) and a biotin tag, which was subsequently induced with streptavidin (SA) to form an oligomeric poly-IgA mimic. Both uninduced rIgA (mono-rIgA) and polymeric SA-rIgA (poly-rIgA) were injected intravenously into Wistar rats. Plasma IgA levels and renal and liver histology were examined in a time series. In contrast to mono-rIgA, this synthetic poly-rIgA analog formed renal deposits exclusively in the glomerulus and were mostly cleared in 3 h. However, repeated daily injections for 12 days caused long-lasting and stronger glomerular IgA deposition together with IgG and complement C3, in association with mesangial cell proliferation, matrix expansion, and variable degrees of albuminuria and hematuria that phenocopied IgAN. Ex vivo, poly-rIgA bound cultured mesangial cells and elicited cytokine production, in addition to activating plasma C3 that was consistent with the actions of IgA immune complexes in IgAN pathogenesis. Remarkably, the kidneys were able to reverse all pathologic manifestations and restore normal glomerular histology 2 weeks after injections were halted. The synthetic model showed the kinetics between the intricate balance of renal deposition and clearance, as well as glomerular plasticity towards healing. Together, the results revealed a priming effect of existing deposits in promoting stronger and longer-lasting IgA deposition to cause renal damage. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A single-cell survey of the human glomerulonephritis

Glomerulonephritis is the one of the major causes of the end-stage kidney disease, whereas the pathological process of glomerulonephritis is still not completely understood. Single-cell RNA sequencing (scRNA-seq) emerges to be a powerful tool to evaluate the full heterogeneity of kidney diseases. To reveal cellular gene expression profiles of glomerulonephritis, we performed scRNA-seq of 2 human kidney transplantation donor samples, 4 human glomerulonephritis samples, 1 human malignant hypertension (MH) sample and 1 human chronic interstitial nephritis (CIN) sample, all tissues were taken from the biopsy. After filtering the cells with < 200 genes and > 10% mitochondria (MT) genes, the resulting 14 932 cells can be divided into 20 cell clusters, consistently with the previous report, in disease samples dramatic immune cells infiltration was found, among which a proximal tubule (PT) subset characterized by wnt-β catenin activation and a natural killer T (NKT) subset high expressing LTB were found. Furthermore, in the cluster of the podocyte, three glomerulonephritis related genes named FXYD5, CD74 and B2M were found. Compared with the mesangial of donor, the gene CLIC1 and RPS26 were up-regulated in mesangial of IgA nephropathy(IgAN), whereas the gene JUNB was up-regulated in podocyte of IgAN in comparison with that of donor. Meanwhile, some membranous nephropathy (MN) high expressed genes such as HLA-DRB5, HLA-DQA2, IFNG, CCL2 and NR4A2, which involve in highest enrichment pathway, display the cellular-specific expression style, whereas monocyte marker of lupus nephritis (LN) named TNFSF13B was also found and interferon alpha/beta signalling pathway was enriched in B and NKT of LN comparing with donor. By scRNA-seq, we first defined the podocyte markers of glomerulonephritis and specific markers in IgA, MN and LN were found at cellular level. Furthermore, the critical role of interferon alpha/beta signalling pathway was enriched in B and NKT of LN was declared.

microRNA-630 Regulates Underglycosylated IgA1 Production in the Tonsils by Targeting TLR4 in IgA Nephropathy

IgA nephropathy (IgAN) is the most common primary glomerular disease. The characteristic pathology involves immune complexes formed by the deposition of IgA1 and underglycosylated IgA1 aggregates in the mesangial area, which may be accompanied by the deposition of IgG and/or IgM and complement components. However, the molecular mechanisms of IgAN remain unclear. In the present study, microarray analysis showed that the expression of microRNA-630 (miR-630) was significantly reduced in palatal tonsils from IgAN patients compared with chronic tonsillitis. Additionally, bioinformatic analysis showed that Toll-like receptor 4 (TLR4) was the predicted target gene of miR-630 and was regulated by miR-630. When miR-630 was overexpressed in palatal tonsil mononuclear cells from IgAN patients, the expression of TLR4 was reduced and the content of IgA1 in the cell culture supernatant was decreased, and the level of galactosylation in the IgA1 hinge region was increased. Moreover, immunohistochemical analysis showed that the expression of TLR4 in IgAN patients was significantly increased. After knocking down the expression of TLR4, both the concentration of IgA1 and the binding force of IgA1 with broad bean lectin were significantly reduced in IgAN. Furthermore, the mechanism study demonstrated that TLR4 might regulate the expression of IL-1β and IL-8 through NF-κB signaling pathway to modulate the concentration of IgA1 and the glycosylation level of IgA1. This interesting finding may offer new insight into the molecular mechanism of IgAN.

MicroRNA-27a-3p directly targets FosB to regulate cell proliferation, apoptosis, and inflammation responses in immunoglobulin a nephropathy

Immunoglobulin A nephropathy (IgAN) constitutes the most common primary glomerulonephritis worldwide; however, the exact pathogenesis of IgAN is unknown. Previous genome-wide analysis of microRNA (miRNA) expression in the kidney has confirmed that miRNAs are closely related to the pathological changes of IgAN. Accordingly, in this study we found that miR-27a-3p is upregulated in IgAN kidney tissues in addition to human podocytes and tubule epithelial HK2 but not mesangial cells. Methylthiazolyldiphenyl-tetrazolium bromide (MTT), flow cytometry, real-time polymerase chain reaction, western blot, and enzyme-linked immunosorbent assays were used to verify the regulatory effects of miR-27a-3p and its inhibition on cell proliferation, apoptosis, and release of inflammatory factors in podocytes and HK2 cells. The target genes of miR-27a-3p were predicted using bioinformatics software; the identity of FosB as a target gene of miR-27a-3p was confirmed by luciferase report assay and western blot. Overall, our findings demonstrated that miR-27a-3p regulates cell apoptosis, cell proliferation, and the release of inflammatory cytokines of human podocytes and HK2 cells by directly targeting FosB. Our results therefore suggested that miR-27a-3p might be associated with the pathophysiology of IgAN and may represent a potential target for further studies related to IgAN mechanism or therapeutics.

The upregulation of miR-98-5p affects the glycosylation of IgA1 through cytokines in IgA nephropathy

OBJECTIVE

Increases in galactose-deficient IgA1 (Gd-IgA1) play a crucial role in the pathogenesis of IgA nephropathy (IgAN), and several recent experiments have shown that microRNAs (miRNAs) are involved in regulating the development and physiological function of the kidney. The aims of this study were to identify miRNAs that can affect the pathogenesis of IgAN and reveal the underlying regulatory mechanism of IgA1 glycosylation in peripheral blood.

METHODS

The differentially expressed miRNAs in peripheral blood mononuclear cells (PBMCs) between IgAN patients and healthy controls were screened by high-throughput sequencing, and the targets of these miRNAs were predicted and verified by dual-luciferase reporter assays. We also explored the miRNA regulation of Gd-IgA1 through the transfection of miRNA mimics and related plasmids.

RESULTS

The high-throughput sequencing results showed that miR-98-5p was more highly expressed in the PBMCs of IgAN patients compared with healthy controls, and the luciferase reporter gene system confirmed that miR-98-5p might target chemokine ligand 3 (CCL3). The transfection of si-CCL3 confirmed that a decrease in CCL3 can affect the expression of interleukin-6 (IL-6) and C1GALT1. The overexpression of miR-98-5p in PBMCs through the transfection of miR-98-5p mimic reduced the CCL3 and C1GALT1 levels and increased the IL-6 levels, and these changes in PBMCs were attenuated by cotransfection with the CCL3 plasmid.

CONCLUSION

The results showed that in PBMCs, miR-98-5p can target CCL3 to decrease its expression and thereby increase the IL-6 levels, and the resulting increase in IL-6 can decrease C1GALT1 expression. Therefore, miR-98-5p might be involved in the development of IgAN.

Role of Epstein-Barr Virus in Pathogenesis and Racial Distribution of IgA Nephropathy

IgA nephropathy (IgAN) is the dominant type of primary glomerulonephritis worldwide. However, IgAN rarely affects African Blacks and is uncommon in African Americans. Polymeric IgA1 with galactose-deficient hinge-region glycans is recognized as auto-antigen by glycan-specific antibodies, leading to formation of circulating immune complexes with nephritogenic consequences. Because human B cells infected in vitro with Epstein-Barr virus (EBV) secrete galactose-deficient IgA1, we examined peripheral blood B cells from adult IgAN patients, and relevant controls, for the presence of EBV and their phenotypic markers. We found that IgAN patients had more lymphoblasts/plasmablasts that were surface-positive for IgA, infected with EBV, and displayed increased expression of homing receptors for targeting the upper respiratory tract. Upon polyclonal stimulation, these cells produced more galactose-deficient IgA1 than did cells from healthy controls. Unexpectedly, in healthy African Americans, EBV was detected preferentially in surface IgM- and IgD-positive cells. Importantly, most African Blacks and African Americans acquire EBV within 2 years of birth. At that time, the IgA system is naturally deficient, manifested as low serum IgA levels and few IgA-producing cells. Consequently, EBV infects cells secreting immunoglobulins other than IgA. Our novel data implicate Epstein-Barr virus infected IgA⁺ cells as the source of galactose-deficient IgA1 and basis for expression of relevant homing receptors. Moreover, the temporal sequence of racial-specific differences in Epstein-Barr virus infection as related to the naturally delayed maturation of the IgA system explains the racial disparity in the prevalence of IgAN.

Complement and Complement Targeting Therapies in Glomerular Diseases

The complement cascade is part of the innate immune system whose actions protect hosts from pathogens. Recent research shows complement involvement in a wide spectrum of renal disease pathogenesis including antibody-related glomerulopathies and non-antibody-mediated kidney diseases, such as C3 glomerular disease, atypical hemolytic uremic syndrome, and focal segmental glomerulosclerosis. A pivotal role in renal pathogenesis makes targeting complement activation an attractive therapeutic strategy. Over the last decade, a growing number of anti-complement agents have been developed; some are approved for clinical use and many others are in the pipeline. Herein, we review the pathways of complement activation and regulation, illustrate its role instigating or amplifying glomerular injury, and discuss the most promising novel complement-targeting therapies.

Value of biomarkers for predicting immunoglobulin A vasculitis nephritis outcome in an adult prospective cohort

Background

Henoch-Schönlein purpura, more recently renamed immunoglobulin A vasculitis (IgAV), is a systemic vasculitis characterized by IgA deposits. The current markers used to assess IgAV inaccurately evaluate the risk of nephritis occurrence and its long-term outcomes. The current study assessed biomarkers of nephritis outcomes.

Methods

This French multicentre prospective study enrolled 85 adult patients at the time of disease onset. Patients were assessed for clinical and biological parameters and re-examined after 1 year. Immunoglobulins, cytokines, IgA glycosylation, IgA complexes and neutrophil gelatinase-associated lipocalin (NGAL) concentrations were assessed in blood and urine.

Results

We identified 60 patients with IgAV-related nephritis (IgAV-N) and 25 patients without nephritis (IgAV-woN). At the time of inclusion (Day 1), the serum levels of galactose-deficient IgA1 (Gd-IgA1) and urinary concentrations of IgA, IgG, IgM, NGAL, interleukin (IL)-1β, IL-6, IL-8, IL-10, IgA-IgG and IgA-sCD89 complexes were higher in the IgAV-N patients than in the IgAV-woN patients (P < 0.005 for all comparisons). After follow-up (1 year), 22 patients showed a poor outcome. Among the tested markers, urine IgA at disease onset adequately reclassified the risk of poor outcome over conventional clinical factors, including estimated glomerular filtration rate, proteinuria and age (continuous net reclassification improvement = 0.72, P = 0.001; integrated discrimination improvement = 0.13, P = 0.009) in IgAV patients.

Conclusions

Taken together, these results showed that serum Gd-IgA1 and urinary IgA, IgG, IgM, NGAL, IL-1β, IL-6, IL-8, IL-10, IgA-IgG and IgA-sCD89 complexes were associated with nephritis in IgAV patients. Urinary IgA level may improve patient risk stratification for poor outcome.

The role of complement in IgA nephropathy

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

A Proliferation Inducing Ligand (APRIL) targeted antibody is a safe and effective treatment of murine IgA nephropathy

IgA nephropathy (IgAN) is the most prevalent primary chronic glomerular disease for which no safe disease-specific therapies currently exist. IgAN is an autoimmune disease involving the production of autoantigenic, aberrantly O-glycosylated IgA1 and ensuing deposition of nephritogenic immune complexes in the kidney. A Proliferation Inducing Ligand (APRIL) has emerged as a key B-cell-modulating factor in this pathogenesis. Using a mouse anti-APRIL monoclonal antibody (4540), we confirm both the pathogenic role of APRIL in IgAN and the therapeutic efficacy of antibody-directed neutralization of APRIL in the grouped mouse ddY disease model. Treatment with 4540 directly translated to a reduction in relevant pathogenic mechanisms including suppressed serum IgA levels, reduced circulating immune complexes, significantly lower kidney deposits of IgA, IgG and C3, and suppression of proteinuria compared to mice receiving vehicle or isotype control antibodies. Furthermore, we translated these findings to the pharmacological characterization of VIS649, a highly potent, humanized IgG2κ antibody targeting and neutralizing human APRIL through unique epitope engagement, leading to inhibition of APRIL-mediated B-cell activities. VIS649 treatment of non-human primates showed dose-dependent reduction of serum IgA levels of up to 70%. A reduction of IgA⁺, IgM⁺, and IgG⁺ B cells was noted in the gut-associated mucosa of VIS649-treated animals. Population-based modeling predicted a favorable therapeutic dosing profile for subcutaneous administration of VIS649 in the clinical setting. Thus, our data highlight the potential therapeutic benefit of VIS649 for the treatment of IgAN.

Recruitment of CXCR3+ T cells into injured tissues in adult IgA vasculitis patients correlates with disease activity

OBJECTIVES

Adult immunoglobulin A vasculitis (IgAV) is an immune complex small vessel vasculitis. So far, the involvement of T cells in this pathology has been poorly studied. The aim of this study was to analyze T-cell homeostasis as well as cytokine and chemokine concentrations in the blood and tissues of IgAV patients.

METHODS

T cells, cytokine and chemokine concentrations were analyzed in peripheral blood using flow cytometry and multiplex assays. T-cell infiltrates in the kidney and the skin were characterized by immunohistochemistry. This study prospectively included 44 adult patients with biopsy-proven IgAV and 24 age- and sex-matched healthy controls.

RESULTS

We observed reduced proportions of circulating CXCR5-and CXCR3-expressing memory CD4 T cells at diagnosis but normal values at remission. The plasma levels of Th1-related cytokines (IL-12, IL-27 and IFNγ) and of the TFH-related cytokine, IL-21, were paradoxically not reduced in patients. We observed increased plasma concentrations of the CXCR5 ligand, CXCL13, and of the CXCR3 ligands, CXCL10/11, suggesting a potential relocation of the corresponding T cells into inflamed tissues. We then confirmed the recruitment of CXCR3-expressing T cells into the skin and kidneys. In the skin, T-cell infiltrates mainly co-localized with damaged dermal small vessels. Finally, patients with the largest kidney T-cell infiltrates were also those with the highest proteinuria.

CONCLUSION

Altogether, our results strongly suggest that, in IgAV patients, CXCL10/11 orchestrate the recruitment of CXCR3-expressing T cells in injured tissues, contributing to tissue damage and disease activity.

Serum immunoglobulin G provides early risk prediction in immunoglobulin A nephropathy

BACKGROUND

Immunoglobulin A (IgA) nephropathy (IgAN) is a common primary glomerular disease that potentially leads to renal failure, risk prediction of declining kidney function is crucial for early clinical management. Immunoglobulin G (IgG) is an important constituent of the immune system and serves as the preferred therapeutic target in human autoimmune diseases. However, its role in the progression of IgAN is unclear.

METHODS

From May 2009 to April 2014, 455 patients diagnosed with IgAN at the Second Xiangya Hospital were enrolled in this study; the median follow-up was 42.2 months. All subjects were divided into four groups according to IgG level quartiles. The study endpoint was end-stage renal disease (ESRD) or an irreversible 50% estimated glomerular filtration rate (eGFR) reduction. Clinical data and pathological features of renal biopsy specimens were collected.

RESULTS

Among IgAN patients, serum IgG levels were directly correlated with the levels of serum albumin and serum IgA but reversely correlated with body weight, systolic blood pressure, and serum creatinine and cholesterol levels. According to stratified analysis of serum IgG, the proportions of composite renal endpoints among the enrolled IgAN patients in the serum IgG concentration subgroups 1 (<7.86), 2 (7.86-10.30), 3 (10.31-12.70), and 4 (>12.71 g/l) were 9.6%, 9.2%, 3.7%, and 3.7% respectively. Importantly, cumulative renal survival rates were significantly higher in the patients with increased serum IgG (p = 0.0114). Serum IgG was also predictive of renal survival, with an HR of 0.745 (95% CI, 0.614 to 0.905, p = 0.003) after adjusting for significant factors in the univariate Cox regression and an HR of 0.871 (95% CI, 0.780 to 0.973, p = 0.014) adjusting for traditional risk factors of IgAN.

CONCLUSION

These findings demonstrate that a decreased serum IgG level at the time of renal biopsy is independently associated with a poor renal outcome in IgAN patients.

Aberrant Glycosylation of the IgA1 Molecule in IgA Nephropathy

IgA nephropathy, the most common primary glomerulonephritis in the world and a frequent cause of end-stage renal disease, is characterized by typical mesangial deposits of IgA1, as described by Berger and Hinglaise in 1968. Since then, it has been discovered that aberrant IgA1 O-glycosylation is involved in disease pathogenesis. Progress in glycomic, genomic, clinical, analytical, and biochemical studies has shown autoimmune features of IgA nephropathy. The autoimmune character of the disease is explained by a multihit pathogenesis model, wherein overproduction of aberrantly glycosylated IgA1, galactose-deficient in some O-glycans, by IgA1-secreting cells leads to increased levels of circulatory galactose-deficient IgA1. These glycoforms induce production of autoantibodies that subsequently bind hinge-region of galactose-deficient IgA1 molecules, resulting in the formation of nephritogenic immune complexes. Some of these complexes deposit in the kidney, activate mesangial cells, and incite glomerular injury. Thus, galactose-deficient IgA1 is central to the disease process. In this article, we review studies concerning IgA1 O-glycosylation that have contributed to the current understanding of the role of IgA1 in the pathogenesis of IgA nephropathy.

Gene alterations in monocytes are pathogenic factors for immunoglobulin a nephropathy by bioinformatics analysis of microarray data

Background

Immunoglobulin A nephropathy (IgAN) is the most frequent primary glomerulopathy worldwide. The study aimed to provide potential molecular biomarkers for IgAN management.

Methods

The public gene expression profiling GSE58539 was utilized, which contained 17 monocytes samples (8 monocytes samples isolated from IgAN patients and 9 monocytes samples isolated from healthy blood donors). Firstly, differentially expressed genes (DEGs) between the two kinds of samples were identified by limma package. Afterwards, pathway enrichment analysis was implemented. Thereafter, protein-protein interaction (PPI) network was constructed and key nodes in PPI network were predicted using four network centrality analyses. Ultimately, gene functional interaction (FI) was constructed according to expressions in each sample, and then module network was extracted from FI network.

Results

A total of 678 DEGs were screened out, of these, 72 DEGs were identified as crucial nodes in PPI network that could well distinguish IgAN and healthy samples. In particular, IL6, TNF, IL1B, PRKACA and CCL20 were closely related to pathways such as hematopoietic cell lineage, apoptosis and Toll-like receptor (TLR) signaling pathway. Moreover, 12 genes in the FI network belonged to the 72 identified key nodes, such as CCL20, HDAC10, FPR2 and PRKACA, which were also key genes in 4 module networks.

Conclusions

Several crucial genes were identified in monocytes of IgAN patients, such as IL6, TNF, IL1B, CCL20, PRKACA, FPR2 and HDAC10. These genes might co-involve in pathways such as TLR and apoptosis signaling during IgAN progression.

Biomarkers for IgA nephropathy on the basis of multi-hit pathogenesis

IgA nephropathy (IgAN) is the most prevalent glomerular disease worldwide and is associated with a poor prognosis. Development of curative treatment strategies and approaches for early diagnosis is necessary. Renal biopsy is the gold standard for the diagnosis and assessment of disease activity. However, reliable biomarkers are needed for the noninvasive diagnosis of this disease and to more fully delineate the risk of progression. With regard to the pathogenesis of IgAN, the multi-hit hypothesis, including production of galactose-deficient IgA1 (Gd-IgA1; Hit 1), IgG or IgA autoantibodies that recognize Gd-IgA1 (Hit 2), and their subsequent immune complexes formation (Hit 3) and glomerular deposition (Hit 4), has been widely supported by many studies. Although the prognostic values of several biomarkers have been discussed, we recently developed a highly sensitive and specific diagnostic method by measuring serum levels of Gd-IgA1 and Gd-IgA1-containing immune complexes. In addition, urinary Gd-IgA1 may represent a disease-specific biomarker for IgAN. We also confirmed that there is a significant correlation between serum levels of these effector molecules and disease activity, suggesting that each can be considered a practical surrogate marker of therapeutic response. Thus, these disease-oriented specific serum and urine biomarkers may be useful for screening of potential IgAN with isolated hematuria, earlier diagnosis, disease activity, and eventually, response to treatment. In this review, we discuss these concepts, with a focus on potential clinical applications of these biomarkers.

Comparative Efficacy and Safety of Therapies in IgA Nephropathy: A Network Meta-analysis of Randomized Controlled Trials

The present study aims to compare the relative efficacy and safety of different interventions for IgA nephropathy (IgAN) with proteinuria more than 1 g/d by using network meta-analysis. We searched PubMed, Embase, and the Cochrane Library for studies compared the rate of clinical remission and/or end-stage renal disease (ESRD) and/or serious adverse events in IgAN patients with proteinuria (>1 g/d). The surface under the cumulative ranking area (SUCRA) was calculated to rank the interventions. A total of 21 randomized controlled trials with 1822 participants were included for the comparisons of 7 interventions. The rank of the most effective treatments to induce clinical remission was renin−angiotensin system inhibitors (RASi) plus urokinase, steroid plus tonsillectomy, and RASi plus steroid with a SUCRA of 0.912, 0.710, and 0.583, respectively. As for the prevention of ESRD or doubling of serum creatinine, RASi plus steroid (SUCRA 0.012) was the most effective, followed by RASi (SUCRA 0.282) and steroid (SUCRA 0.494), leaving mycophenolate mofetil as the least effective (SUCRA 0.644). There was no statistical difference among all interventions in the occurrence of serious adverse events. The current network meta-analysis demonstrated for the first time that RASi plus steroid is probably the best therapeutic choice, not only for reducing proteinuria but also for maintaining long-term renal protection.

Glucocorticoids Reduce Aberrant O-Glycosylation of IgA1 in IgA Nephropathy Patients

BACKGROUND/AIMS

IgA nephropathy is associated with aberrant O-glycosylation of IgA1, which is recognized by autoantibodies leading to the formation of circulating immune complexes. Some of them, after deposition into kidney mesangium, trigger glomerular injury. In patients with active disease nonresponding to angiotensin-converting enzyme inhibitors or angiotensin II blockers, corticosteroids are recommended.

METHODS

The relationship between the corticosteroid therapy and serum levels of IgA, aberrantly O-glycosylated IgA1, IgA-containing immune complexes and their mesangioproliferative activity was analyzed in IgA nephropathy patients and disease and healthy controls.

RESULTS

Prednisone therapy significantly reduced proteinuria and levels of serum IgA, galactose-deficient IgA1, and IgA-IgG immune complexes in IgA nephropathy patients and thus reduced differences in all of the above parameters between IgAN patients and control groups. A moderate but not significant reduction of mesangioproliferative potential of IgA-IgG immune complexes and IgA sialylation was detected.

CONCLUSION

The prednisone therapy reduces overall aberrancy in IgA1 O-glycosylation in IgA nephropathy patients, but the measurement of IgA1 parameters does not allow us to predict the prednisone therapy outcome in individual patients.

The natural history of immunoglobulin M nephropathy in adults

Background

Immunoglobulin M (IgM) nephropathy is an idiopathic glomerulonephritis characterized by diffuse mesangial deposition of IgM. IgM nephropathy has been a controversial diagnosis since it was first reported, and there are few data identifying specific pathological features that predict the risk of progression of renal disease.

Methods

We identified 57 cases of IgM nephropathy among 3220 adults undergoing renal biopsy at our institution. Biopsies had to satisfy the following three criteria to meet the definition of IgM nephropathy in this study: (i) dominant mesangial staining for IgM, (ii) mesangial deposits on electron microscopy (EM) and (iii) exclusion of systemic disease.

Results

The median age was 42 years and 24 patients were male. Thirty-nine per cent of patients presented with the nephrotic syndrome, 49% presented with non-nephrotic proteinuria and 39% had eGFR <60 mL/min. The median post-biopsy follow-up was 40 months and serum creatinine had doubled in 31% by 5 years. Of histological parameters, glomerular sclerosis and tubular atrophy, but not mesangial proliferation, were risk factors for renal insufficiency. Thirty-nine per cent of nephrotic patients achieved complete remission, and outcome was significantly worse in those who did not respond to treatment. Focal segmental glomerulosclerosis was diagnosed in 80% of those undergoing repeat renal biopsy, despite ongoing mesangial IgM deposition.

Conclusions

We propose criteria for a consensus definition of IgM nephropathy.

Biomarkers of IgA vasculitis nephritis in children

Henoch–Schönlein purpura is a systemic vasculitis characterized by IgA deposits, which target the skin, joints, and kidneys, among other organs. In children, prognosis is often good but little is known about biomarkers of pediatric nephritis. We hypothesized that biological markers, including cytokines, immunoglobulins, IgA-immune complexes, IgA glycosylation and neutrophil gelatinase-associated lipocalin (NGAL), may discriminate IgA vasculitis (IgAV) pediatric patients with renal involvement from those without renal involvement. Fifty children at the time of IgAV rash between 2010 and 2015 were prospectively enrolled and compared to 21 controls. All patients were assessed for clinical and biological parameters at the time of diagnosis, including the levels of cytokines, immunoglobulins, immune complexes, IgA glycosylation and NGAL in serum and urine. Among IgAV patients, 33 patients exhibited nephritis (IgAV-N) and 17 children were without nephritis (IgAV-woN). The serum level of galactose-deficient (Gd)-IgA1 (p<0.01) and the urinary concentrations of IgA, IgG, IgM, IL-6, IL-8, IL-10, IgA-IgG complexes and IgA-sCD89 complexes (p<0.001 for all) were higher in the IgAV-N patients than in the IgAV-woN patients. Among those markers, urinary IgA and IgM had the highest AUC (0.86 and 0.87 respectively, p<0.0001). This prospective cohort study furthers our understanding of the pathophysiology of IgAV. We identified biomarkers that are able to distinguish patients initially with or without nephritis. To conclude, serum Gd-IgA1 and urinary IgA, IgG, IgM, IL-6, IL-8, IL-10, and IgA-IgG and IgA-sCD89 complexes could identify IgAV pediatric patients with renal involvement at the time of diagnosis.

Patients With IgA Nephropathy Have Altered Levels of Immunomodulatory C19 Steroids. Glucocorticoid Therapy With Addition of Adrenal Androgens May Be the Choice

Glucocorticoid (GC) therapy is one of the methods of choices for treatment of autoimmune diseases (ADs). In addition, adrenal androgens are known as immunoprotective GC-antagonists. Adrenal steroids preferentially influence the Th1-components over the Th2 ones. We investigated steroid metabolome (using gas chromatography-mass spectrometry) in healthy controls (H), GC-untreated patients with ADs different from IgA nephropathy (U), GC-treated patients with ADs different from IgA nephropathy (T) and in patients with IgA nephropathy (IgAN), which were monitored on the beginning (N0), after one week (N1) and after one month (N2) of prednisolone therapy (60 mg of prednisolone/day/m2 of body surface). Between-group differences were assessed by one-way ANOVA, while the changes during the therapy were evaluated by repeated measures ANOVA. The ANOVA testing was followed by Duncan’s multiple comparisons. IgAN patients and patients with other ADs exhibited lack of adrenal androgens due to attenuated activity of adrenal zona reticularis (ZR). Androgen levels including their 7α-, 7β-, and 16α-hydroxy-metabolites were further restrained by GC-therapy. Based on these results and data from the literature, we addressed the question, whether a combination of GCs with Δ5-steroids or their more stable synthetic derivatives may be optimal for the treatment of antibodies-mediated ADs.

The interaction effect of rs4077515 and rs17019602 increases the susceptibility to IgA nephropathy

Background

Immunoglobulin A nephropathy (IgAN), the most common form of primary glomerular diseases worldwide, is a complex multifactorial disease. Previous genome wide association studies (GWAS) reported that variants CARD9 and VAV3 genes were associated with immunoregulation and susceptibility to IgAN. In this study, we further validated the associations and explored the interaction effect of rs4077515 and rs17019602 in IgAN patients.

Results

There was no significant correlation between the two variants and IgAN (P > 0.05). The gene-gene analysis showed that rs4077515 and rs17019602 had interaction effect on the susceptibility to IgAN. For additive interaction, the CT or TT of rs4077515 and GG of 17019602 genotype combination conferred a 2.56-fold risk of IgAN reference to CC of 4077515 and AA of 17019602 (OR = 2.56, 95% CI: 0.98–6.69, P = 0.049). In our study, clinical data was available for 543 patients. In comparison, neither rs4077515 nor rs17019602 showed significant association between genotype distribution and clinical parameters in IgAN patients (P > 0.05).

Materials and Methods

The case-control study included 586 patients with IgAN and 606 healthy controls. Variant rs4077515 of CARD9 gene and rs17019602 of VAV3 gene were genotyped by the ABI TaqMan probe assay.

Conclusions

The interaction effect of the variants of CARD9 and VAV3 genes increases the susceptibility to IgAN.

Efficacy and safety of mycophenolate mofetil in patients with IgA nephropathy: an update meta-analysis

Background

The application of mycophenolate mofetil (MMF) in treating patients with immunoglobulin A nephropathy (IgAN) remains uncertain. This update meta-analysis was performed to re-evaluate the therapeutic potential of MMF in IgAN.

Methods

Articles were obtained by searching the electronic databases without language restriction. Randomized controlled trials studying the role of MMF in treating IgAN were collected. The quality of included studies was critically evaluated. Data analyses were performed by using RevMan 5.3 software.

Results

A total of 297 articles were screened and eight articles were finally included. Among the eight randomized controlled trials, five and three were high quality and low quality, respectively. Both fixed-effect and random-effect model were used. Pooled results by combining all the eight studies suggested that IgAN patients in MMF group had a higher remission rate than that in control group. Compared to placebo or corticosteroid monotherapy, MMF monotherapy exerted a higher remission rate and side effect rate in both main analysis and subgroup analysis by human race. Compared to corticosteroid plus other immunosuppressive agent therapy, corticosteroid plus MMF therapy had a higher remission rate, lower serum creatinine doubling rate, progression to end-stage renal disease rate and side effects rate. Subgroup analysis by therapeutic regimen further confirmed these results between corticosteroid plus MMF therapy and corticosteroid plus cyclophosphamide therapy. Funnel-plot displayed a symmetrical figure, indicating no publication bias existed.

Conclusions

MMF has the potential in treatment of IgAN, especially for Asians. The evidence currently available shows that MMF monotherapy has a more efficacy but higher side effects when compared to placebo or corticosteroid monotherapy in treatment of Asians with IgAN. While MMF combined with corticosteroid regimen has a more efficacy and lower side effects when compared with corticosteroid plus cyclophosphamide regimen.

Inhibition of STAT3 Signaling Reduces IgA1 Autoantigen Production in IgA Nephropathy

Introduction

IgA nephropathy is a chronic renal disease characterized by mesangial immunodeposits that contain autoantigen, which is aberrantly glycosylated IgA1 with some hinge-region O-glycans deficient in galactose. Macroscopic hematuria during an upper respiratory tract infection is common among patients with IgA nephropathy, which suggests a connection between inflammation and disease activity. Interleukin-6 (IL-6) is an inflammatory cytokine involved in IgA immune response. We previously showed that IL-6 selectively increases production of galactose-deficient IgA1 in IgA1-secreting cells from patients with IgA nephropathy.

Methods

We characterized IL-6 signaling pathways involved in the overproduction of galactose-deficient IgA1. To understand molecular mechanisms, IL-6 signaling was analyzed by kinomic activity profiling and Western blotting, followed by confirmation assays using siRNA knock-down and small-molecule inhibitors.

Results

STAT3 was differentially activated by IL-6 in IgA1-secreting cells from patients with IgA nephropathy compared with those from healthy control subjects. Specifically, IL-6 induced enhanced and prolonged phosphorylation of STAT3 in the cells from patients with IgA nephropathy, which resulted in overproduction of galactose-deficient IgA1. This IL-6−mediated overproduction of galactose-deficient IgA1 could be blocked by small molecule inhibitors of JAK/STAT signaling.

Discussion

Our results revealed that IL-6−induced aberrant activation of STAT3-mediated overproduction of galactose-deficient IgA1. STAT3 signaling pathway may thus represent a new target for disease-specific therapy of IgA nephropathy.

Immunoglobulin Glycosylation Effects in Allergy and Immunity

PURPOSE OF REVIEW

The aim of this review will be to familiarize the reader with the general area of antibody (Ab) glycosylation and to summarize the known functional roles of glycosylation and how glycan structure can contribute to various disease states with emphasis on allergic disease.

RECENT FINDINGS

Both immunoglobulin (Ig) isotype and conserved Fc glycosylation sites often dictate the downstream activity of an Ab where complexity and degree of glycosylation contribute to its ability to bind Fc receptors (FcRs) and activate complement. Most information on the effects of glycosylation center on IgG in cancer therapy and autoimmunity. In cancer therapy, glycosylation modifications that enhance affinity for activating FcRs are utilized to facilitate immune-mediated tumor cell killing. In autoimmunity, disease severity has been linked to alterations in the presence, location, and composition of Fc glycans. Significantly less is understood about the role of glycosylation in the setting of allergy and asthma. However, recent data demonstrate that glycosylation of IgE at the asparagine-394 site of Cε3 is necessary for IgE interaction with the high affinity IgE receptor but, surprisingly, glycosylation has no effect on IgE interaction with its low-affinity lectin receptor, CD23. Variations in the specific glycoform may modulate the interaction of an Ig with its receptors. Significantly more is known about the functional effects of glycosylation of IgG than for other Ig isotypes. Thus, the role of glycosylation is much better understood in the areas of autoimmunity and cancer therapy, where IgG is the dominant isotype, than in the field of allergy, where IgE predominates. Further work is needed to fully understand the role of glycan variation in IgE and other Ig isotypes with regard to the inhibition or mediation of allergic disease.

Mesangial C4d deposition may predict progression of kidney disease in pediatric patients with IgA nephropathy

BACKGROUND

Data on the risk factors for chronic kidney disease in children with immunoglobulin A nephropathy (IgAN) are scarce. This study was aimed at investigating whether glomerular C4d immunostaining is a prognostic marker in pediatric IgAN.

METHODS

In this retrospective cohort study, 47 patients with IgAN biopsied from 1982 to 2010 were evaluated. Immunohistochemistry for C4d was performed in all cases. For analysis, patients were grouped according to positivity or not for C4d in the mesangial area. Primary outcome was a decline in baseline estimated glomerular filtration rate (eGFR) by 50% or more.

RESULTS

Median follow-up was 8.3 years. Median renal survival was 13.7 years and the probability of a 50% decline in eGFR was 13% over 10 years. Nine children exhibited the primary outcome and 4 developed end-stage renal disease (ESRD). Compared with C4d-negative patients (n = 37), C4d-positive patients (n = 10) presented higher baseline proteinuria (1.66 ± 0.68 vs 0.47 ± 0.19 g/day/1.73 m2, p < 0.001), a progressive decline in eGFR (−10.04 ± 19.38 vs 1.70 ± 18.51 ml/min/1.73 m2/year; p = 0.045), and more frequently achieved the primary outcome (50.0 vs 10.8%, p = 0.013), and ESRD (30.0 vs 2.7%, p = 0.026). No difference was observed in Oxford classification variables. Baseline proteinuria, endocapillary hypercellularity and mesangial C4d deposition were associated with primary outcome in univariate analysis. Proteinuria and mesangial C4d deposition at baseline independently predicted the decline in eGFR. Renal survival was significantly reduced in C4d-positive patients (8.6 vs 15.1 years in C4d-negative patients, p < 0.001).

CONCLUSIONS

In this exclusively pediatric cohort, positivity for C4d in the mesangial area was an independent predictor of renal function deterioration in IgAN.