Immune complex formation in IgA nephropathy: a case of the 'right' antibodies in the 'wrong' place at the 'wrong' time?

The role of BAFF and APRIL in IgA nephropathy: pathogenic mechanisms and targeted therapies

Immunoglobulin A nephropathy (IgAN), characterized by mesangial deposition of galactose-deficient-IgA1 (Gd-IgA1), is the most common biopsy-proven primary glomerulonephritis worldwide. Recently, an improved understanding of its underlying pathogenesis and the substantial risk of progression to kidney failure has emerged. The "four-hit hypothesis" of IgAN pathogenesis outlines a process that begins with elevated circulating levels of Gd-IgA1 that trigger autoantibody production. This results in the formation and deposition of immune complexes in the mesangium, leading to inflammation and kidney injury. Key mediators of the production of Gd-IgA1 and its corresponding autoantibodies are B-cell activating factor (BAFF), and A proliferation-inducing ligand (APRIL), each playing essential roles in the survival and maintenance of B cells and humoral immunity. Elevated serum levels of both BAFF and APRIL are observed in patients with IgAN and correlate with disease severity. This review explores the complex pathogenesis of IgAN, highlighting the pivotal roles of BAFF and APRIL in the interplay between mucosal hyper-responsiveness, B-cell activation, and the consequent overproduction of Gd-IgA1 and its autoantibodies that are key features in this disease. Finally, the potential therapeutic benefits of inhibiting BAFF and APRIL in IgAN, and a summary of recent clinical trial data, will be discussed.

Tofacitinib combined with leflunomide for treatment of psoriatic arthritis with IgA nephropathy: a case report with literature review

Psoriasis is a systemic inflammatory disease that is associated with increased risk of several diseases, such as psoriatic arthritis (PsA), inflammatory bowel disease, and cardiovascular diseases. About 20 to 30% patients with psoriasis subsequently develop PsA. IgA nephropathy is the most common primary glomerular disease world-wide. Psoriasis and IgA nephropathy appear to be associated, but the mechanism underlying this connection is unclear. Tofacitinib and leflunomide are common treatments for psoriatic arthritis. We administered tofacitinib combined with leflunomide to a 38-year-old female patient who presented with PsA and IgA nephropathy. After treatment, she experienced significant reductions in the psoriatic lesions, pain in the right knee joint, and proteinuria. Administration of tofacitinib combined with leflunomide for treatment of a patient who had PsA complicated with IgA nephropathy led to significant resolution of the symptoms of both conditions. These results suggest similarities in the pathogenesis of PsA and IgA nephropathy and a possible new treatment for IgA nephropathy.

Traditional Chinese Medicine in Treating IgA Nephropathy: From Basic Science to Clinical Research

IgA nephropathy (IgAN) is a major cause of chronic kidney disease (CKD) and end-stage renal disease worldwide. Currently, clinical interventions for IgAN are limited, and many patients seek out alternative therapies such as traditional Chinese medicine (TCM). In the last several years, TCM has accumulated ample application experiences and achieved favorable clinical effects. This article summarizes high-quality research from basic science to clinical applications aimed to provide more evidence-based medicine proof for the clinical treatment of IgAN. In summary, qi and yin deficiency accounted for the largest proportion in IgAN patients, and the treatment of IgAN should be based on supplementing qi and nourishing yin. Further, for patients with severe IgAN, the treatment combination of Chinese and Western medicines is better than pure Chinese medicine or hormone therapy. In addition, the pharmacological mechanism of Chinese herbal medicines is mostly based on restoring the immune function, relieving the inflammation damage, and inhibiting proliferation of the glomerular mesangial cells.

Association between Tfh and PGA in children with Henoch-Schönlein purpura

Objective

The aim of this study was to investigate the roles of follicular helper CD4⁺ T cells (Tfh) and serum anti-α-1,4-d-polygalacturonic acid (PGA) antibody in the pathogenesis of Henoch-Schönlein purpura (HSP).

Methods

ELISA was performed to determine serum PGA-IgA and PGA-IgG. Flow cytometry was utilized to determine the peripheral CD4⁺ CXCR5⁺ and CD4⁺ CXCR5⁺ ICOS⁺ Tfh cells. Real-time PCR was conducted to determine the expression of Bcl-6 gene. Then the change of Tfh cells was analyzed, together with the association with the anti-PGA antibody as well as the roles in the pathogenesis of HSP.

Results

Compared with the cases with acute respiratory infection and elective surgery, the proportion of CD4⁺ CXCR5⁺ and CD4⁺ CXCR5⁺ ICOS⁺ Tfh cells in the HSP group showed significant elevation (P < 0.001). A significant correlation was noticed between PGA-IgA and CD4⁺ CXCR5⁺ Tfh cells (r = 0.380 and P = 0.042) and CD4⁺ CXCR5⁺ ICOS⁺ Tfh cells (r = 0.906 and P < 0.001). The expression of Bcl-6 in the HSP group showed no statistical difference compared with that in the acute respiratory infection and the surgery control (P < 0.05).

Conclusion

Increased activity of Tfh cells, which is closely related to mucosal immunity, may be a major contributor in the elevation of PGA-IgA, and Tfh cells and PGA-IgA are closely related to the occurrence of HSP.

An Update on the Current State of Management and Clinical Trials for IgA Nephropathy

IgA nephropathy remains the most common primary glomerular disease worldwide. It affects children and adults of all ages, and is a leading cause of end-stage kidney disease, making it a considerable public health issue in many countries. Despite being initially described over 50 years ago, there are still no disease specific treatments, with current management for most patients being focused on lifestyle measures and renin-angiotensin-aldosterone system blockade. However, significant advances in the understanding of its pathogenesis have been made particularly over the past decade, leading to great interest in developing new therapeutic strategies, and a significant rise in the number of interventional clinical trials being performed. In this review, we will summarise the current state of management of IgAN, and then describe major areas of interest where new therapies are at their most advanced stages of development, that include the gut mucosal immune system, B cell signalling, the complement system and non-immune modulators. Finally, we describe clinical trials that are taking place in each area and explore future directions for translational research.

IgA Nephropathy: An Interesting Autoimmune Kidney Disease

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. It is a leading cause of chronic kidney disease and progresses to end-stage kidney disease in up to 40% of patients about 20 years after diagnosis. Additionally, IgAN is associated with significant mortality. The diagnosis currently necessitates a kidney biopsy, as no biomarker sufficiently specific and sensitive is available to supplant the procedure. Patients display significant heterogeneity in the epidemiology, clinical manifestations, renal progression, and long-term outcomes across diverse racial and ethnic populations. Recent advances in understanding the underlying pathophysiology of the disease have led to the proposal of a four-hit hypothesis supporting an autoimmune process. To date, there is no disease-specific treatment but, with a better understanding of the disease pathogenesis, new therapeutic approaches are currently being tested in clinical trials. In this review, we examine the multiple facets and most recent advances of this interesting disease.

Effects of Hydroxychloroquine on Proteinuria in IgA Nephropathy: A Randomized Controlled Trial

RATIONALE & OBJECTIVE

Despite optimization of renin-angiotensin-aldosterone system (RAAS) inhibition, patients with immunoglobulin A nephropathy (IgAN) and persistent proteinuria remain at risk for kidney failure. We evaluated the efficacy and safety of hydroxychloroquine (HCQ), an immunomodulator, when added to the treatment regimen of patients with IgAN.

STUDY DESIGN

Double-blind, randomized, placebo-controlled, phase 2 clinical trial.

SETTING & PARTICIPANTS

Participants had IgAN (proteinuria with protein excretion of 0.75-3.5g/d and estimated glomerular filtration rate>30mL/min/1.73m²) and were receiving optimized RAAS inhibitor therapy.

INTERVENTIONS

Patients were randomly assigned 1:1 to receive daily oral HCQ or a placebo for 6 months.

OUTCOMES

The primary outcome was percentage change in proteinuria between baseline and 6 months.

RESULTS

60 participants (mean estimated glomerular filtration rate, 53.8mL/min/1.73m²; median urine protein excretion, 1.7g/d) were recruited and randomly assigned to receive HCQ (n=30) or placebo (n=30). Percentage change in proteinuria at 6 months was significantly different between the HCQ group and the placebo group (-48.4% [IQR, -64.2%, -30.5%] vs 10.0% [IQR, -38.7%, 30.6%]; P<0.001, respectively). At 6 months, median proteinuria level was significantly lower in the HCQ group than in the placebo group (0.9 [IQR, 0.6, 1.0] g/d vs 1.9 [IQR, 0.9, 2.6] g/d; P=0.002, respectively). No serious adverse events were recorded during the study in either study group.

LIMITATIONS

The short treatment period and lack of postwithdrawal observations limit conclusions about long-term renoprotective efficacy and safety.

CONCLUSIONS

HCQ in addition to optimized RAAS inhibition significantly reduced proteinuria in patients with IgAN over 6 months without evidence of adverse events. These findings require confirmation in larger treatment trials.

FUNDING

This study was supported by grants from a government entity, the Capital of Clinical Characteristics, and the Applied Research Fund.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT02942381.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

[IgA nephropathy]

IgA nephropathy is the most common form of primary glomerulonephritis worldwide and an important cause of chronic kidney disease and end-stage kidney failure. Its pathophysiology remains in part unsolved but it is recognized as an immune complex disease. Recent years have brought progress in the field through the discovery of several genetic susceptibility loci and the formulation of the multi-hit pathogenesis model. Presentation, clinical course and histology can be extremely variable, making any histological classification still difficult. Indeed, most therapeutic studies until now include patients based only on the severity of clinical criteria but the new classification of Oxford should change that. Only the management of patients with nephropathy with minimal change glomerular lesions and nephrotic syndrome, or extra-capillary glomerulonephritis and rapidly progressive renal failure, is consensual: Corticosteroids alone for the first and associated with immunosuppressive drugs for the latter. The recent Kidney Disease Improving Global Outcomes (KDIGO) consensus treatment guideline is still controversial, especially in light of the last clinical studies. Corticosteroid therapy can be discussed in patients with proteinuria greater than 1 g/day without renal failure. All IgA nephropathy patients should benefit from the global management of chronic glomerular disease, including a renin-angiotensin system blocker in the presence of hypertension or proteinuria.

The mucosa-kidney axis in IgA nephropathy

Links between IgA nephropathy (IgAN) and the mucosa have been recognized since the 1970s. In particular, the observation of visible haematuria induced by respiratory infections in patients with IgAN and the association of IgAN with diseases in which the mucosa plays a part, especially coeliac disease, have been taken as evidence of a mucosa-kidney axis. Here, we review current evidence that links the mucosa, in particular the gastrointestinal mucosa, and IgA produced by the bone marrow with IgAN. Genome-wide association studies in patients with IgAN have identified risk loci in genes involved in the intestinal mucosal integrity and immune network. Furthermore, the systemic immune response to mucosal antigens in IgAN is increased. Moreover, patients with IgAN have an increased reactivity to dietary proteins associated with subclinical intestinal mucosal inflammation. Associations between IgAN and gastrointestinal diseases have also been reported in a small number of patients, but whether these diseases share a common pathogenesis or whether gastrointestinal inflammation exacerbates IgAN is uncertain. Indeed, mucosal alterations such as infections could activate the innate immune system, aggravate a pre-existing IgAN and promote disease manifestations such as macrohaematuria. Various clinical interventions and trials targeting the mucosa or presumed mucosa-associated mechanisms have so far not yielded consistent findings and the results of ongoing trials are eagerly awaited.

Update on immunoglobulin A nephropathy, Part I: Pathophysiology

Immunoglobulin A (IgA) nephropathy is one of the most common glomerulonephritis and its frequency is probably underestimated because in most patients the disease has an indolent course and the kidney biopsy is essential for the diagnosis. In the last years its pathogenesis has been better identified even if still now several questions remain to be answered. The genetic wide association studies have allowed to identifying the relevance of genetics and several putative genes have been identified. The genetics has also allowed explaining why some ancestral groups are affected with higher frequency. To date is clear that IgA nephropathy is related to auto antibodies against immunoglobulin A1 (IgA1) with poor O-glycosylation. The role of mucosal infections is confirmed, but which are the pathogens involved and which is the role of Toll-like receptor polymorphism is less clear. Similarly to date whether the disease is due to the circulating immunocomplexes deposition on the mesangium or whether the antigen is already present on the mesangial cell as a “lanthanic” deposition remains to be clarified. Finally also the link between the mesangial and the podocyte injury and the tubulointerstitial scarring, as well as the mechanisms involved need to be better clarified.

Changes in nephritogenic serum galactose-deficient IgA1 in IgA nephropathy following tonsillectomy and steroid therapy

Background

Recent studies have shown that galactose-deficient IgA1 (GdIgA1) has an important role in the pathogenesis of IgA nephropathy (IgAN). Although emerging data suggest that serum GdIgA1 can be a useful non-invasive IgAN biomarker, the localization of nephritogenic GdIgA1-producing B cells remains unclear. Recent clinical and experimental studies indicate that immune activation tonsillar toll-like receptor (TLR) 9 may be involved in the pathogenesis of IgAN. Here we assessed the possibility of GdIgA1 production in the palatine tonsils in IgAN patients.

Methods

We assessed changes in serum GdIgA1 levels in IgAN patients with clinical remission of hematuria and proteinuria following combined tonsillectomy and steroid pulse therapy. Further, the association between clinical outcome and tonsillar TLR9 expression was evaluated.

Results

Patients (n = 37) were divided into two groups according to therapy response. In one group, serum GdIgA1 levels decreased after tonsillectomy (59%) alone, whereas in the other group most levels only decreased after the addition of steroid pulse therapy to tonsillectomy (41%). The former group showed significantly higher tonsillar TLR9 expression and better improvement in hematuria immediately after tonsillectomy than the latter group.

Conclusions

The present study indicates that the palatine tonsils are probably a major sites of GdIgA1-producing cells. However, in some patients these cells may propagate to other lymphoid organs, which may partially explain the different responses observed to tonsillectomy alone. These findings help to clarify some of the clinical observations in the management of IgAN, and may highlight future directions for research.

In search of a better understanding of IgA nephropathy-associated hematuria

Although microscopic or episodic macroscopic hematuria is the key clinical manifestation of IgA nephropathy (IgAN), still very little is known about its pathogenesis. Cox et al. studied IgAN patients during episodes of macroscopic hematuria and identified an upregulated expression of the chemokine receptor CX3CR1 in their circulating leukocytes. On the basis of a series of additional experimental approaches, they suggest that CX3CR1 and its ligand fractalkine may contribute to the onset of macroscopic hematuria in IgAN.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

Pathological role of tonsillar B cells in IgA nephropathy

Although impaired immune regulation along the mucosa-bone marrow axis has been postulated to play an important role, the pathogenesis of IgA nephropathy (IgAN) is unknown; thus, no disease-specific therapy for this disease exists. The therapeutic efficacy of tonsillectomy or tonsillectomy in combination with steroid pulse therapy for IgAN has been discussed. Although randomized control trials for these therapies are ongoing in Japan, the scientific rationale for these therapies remains obscure. It is now widely accepted that abnormally glycosylated IgA1 and its related immune complex (IC) are probably key molecules for the pathogenesis, and are thus considered possible noninvasive biomarkers for this disease. Emerging evidence indicates that B cells in mucosal infections, particularly in tonsillitis, may produce the nephritogenic IgA. In this paper, we briefly summarize characteristics of the nephritogenic IgA/IgA IC, responsible B cells, and underlying mechanisms. This clinical and experimental information may provide important clues for a therapeutic rationale.

Different pathological roles of toll-like receptor 9 on mucosal B cells and dendritic cells in murine IgA nephropathy

Although pathogenesis of IgA nephropathy (IgAN) is still obscure, pathological contribution of mucosal immunity including production of nephritogenic IgA and IgA immune complex (IC) has been discussed. We have reported that mucosal toll-like receptor (TLR)-9 is involved in the pathogenesis of human and murine IgAN. However, cell-type expressing TLR9 in mucosa remains unclear. To address this, we nasally challenged cell-specific CpG DNA ((i): dendritic cell: (DC), (ii): B cell, (iii): both), known as ligand for TLR9, to IgAN prone mice and analyzed disease phenotype of each group. After 8 times of the weekly administration, every group showed deterioration of glomerular damage. However, CpG-A-group showed clear extension of mesangial proliferative lesions with increase of serum IgA-IgG2a IC and its glomerular depositions, while CpG-B-group showed extent of glomerular sclerotic lesions with increase of serum and glomerular IgA and M2 macrophage infiltration. Present results indicate that mucosal TLR9 on B cells and DC may differently contribute to the progression of this disease via induction of nephritogenic IgA or IgA-IgG IC, respectively. This picture is suggestive for the pathological difference between child and adult IgAN.

The pathogenesis of IgA nephropathy

PURPOSE OF REVIEW

This review will analyze contemporary information concerning the possible pathogenetic mechanisms involved in IgA nephropathy, emphasizing studies in humans rather than experimental animals.

RECENT FINDINGS

Deposition of IgA in the glomeruli, the hallmark of IgA nephropathy, may be a quite common phenomenon. Aberrant O-linked galactosylation of IgA subclass (IgA1) appears to play a central role and 'auto-immunity' to a conformational epitope related to glycans at the hinge region of IgA1 is apparently required. Both a circulating immune complex and an in-situ immune complex mechanism have been advanced. Mediator systems, such as complement activation and engagement of innate immune system, also play prominent roles in determining the clinical onset and severity of disease. Genetic influences are evident but the fine details of genetic predisposition and its impact on outcomes still need to be further elucidated.

SUMMARY

Progress in understanding the details of the pathogenesis of IgA nephropathy will lead to a better means of diagnosis (including noninvasive tests for diagnosis), more accurate individualized prognosis and personalized treatment regimens for this globally distributed and very common primary glomerular disease.

Immune complexes in acute adult-onset Henoch-Schonlein nephritis

BACKGROUND

Adult-onset Henoch-Schönlein purpura nephritis (HSPN) and primary IgA (IgAN) nephropathy have been considered indistinguishable immunohistopathologically and are often considered as two extremes of one disease entity. We postulate that adult-onset Henoch-Schönlein can be distinguished histologically from primary IgAN and that both diseases differ in their immunopathological mechanisms.

METHODS

Twenty consecutive patients with adult-onset HSPN were studied. Serum was analysed for circulating IgA immune complexes; renal biopsies were analysed by light and electron microscopy (EM). As disease controls, 40 IgAN patients were studied.

RESULTS

Intracapillary leukocyte margination was seen in 15 of the 20 patients and cellular crescent formation in all renal biopsies of the HSPN patients. IgAN biopsies showed a few small crescents without intracapillary leukocytes. In 16 HSPN patients, EM was performed and in 10, no dense deposits were found. In all biopsies of IgAN patients, typical 'humps' were found. In 6 of 9 analysed HSPN patients, intermediate to large circulating immune complexes were found, whereas in 4 of 28 analysed patients with primary IgAN small circulating immune complexes were found.

CONCLUSIONS

We consider adult-onset HSPN distinguishable in histology and ultrastructure from primary IgAN. We believe adult-onset Henoch-Schönlein to be a circulating immune complex disease.

Posttransplant recurrence of primary glomerulonephritis

All forms of primary GN may recur after kidney transplantation and potentially jeopardize the survival of the graft. IgA nephritis (IgAN) may recur in approximately one third of patients, more frequently in younger patients and in those with a rapid progression of the original disease. However, with the exception of few patients with rapid progression, there is no evidence that recurrence of IgAN has a deleterious effect on graft survival at least up to 10 years. Recurrence of focal segmental glomerulosclerosis (FSGS) is often associated with nephrotic proteinuria and is more frequent in children, in patients with rapid progression of the original disease, and in those who lost a previous transplant from recurrence. The natural course of recurrent FSGS is usually unfavorable. Early and intensive plasmapheresis may obtain complete or partial response in several patients. Good results have also been reported with rituximab. Idiopathic membranous nephropathy (IMN) may recur in 30% to 40% of patients. The graft survival in patients with IMN is not different than that of patients with other renal diseases. Good results with rituximab have been reported. Membranoproliferative GN (MPGN) may recur in 27% to 65% of patients. The recurrence is more frequent and the prognosis is more severe in type II MPGN. Although recurrent GN is relatively frequent and may worsen the outcome of renal allografts in some patients, its effect is diluted by several other risk-factors that may have a greater effect than recurrent GN on the long-term graft survival.