The kinetics of glomerular deposition of nephritogenic IgA

Effective combination of corticosteroid and cyclosporine A for immunoglobulin A nephropathy with membranoproliferative glomerulonephritis features: a case report

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide with heterogeneous histopathological phenotypes. Although IgAN with membranoproliferative glomerulonephritis (MPGN)-like features has been reported in children and adults, treatment strategies for this rare IgAN subtype have not been established. Here, we present the case of a 56-year-old man with no history of kidney disease who initially presented with nephrotic syndrome. Renal biopsy revealed MPGN-like features with a negative serological workup for secondary causes. Immunofluorescent staining was predominantly positive for IgA in the glomerular mesangial and capillary walls. Galactose-deficient IgA1 staining showed a distribution pattern similar to IgA staining. Electron microscopy revealed disorganized structural deposits in the mesangial and subendothelial regions. Based on clinical and histopathological findings, the patient was diagnosed with primary IgAN. The nephrotic syndrome resolved completely after six months of combined corticosteroids and cyclosporine A (CsA) therapy. Although corticosteroids and CsA were tapered off, hematuria and proteinuria remained in complete remission for years of follow-up. This case demonstrates the importance of recognizing IgAN with MPGN-like features as a histopathological subtype that may benefit from intensive immunosuppressive therapy.

Lessons from IgA Nephropathy Models

IgA nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide; however, the underlying mechanisms of this disease are not fully understood. This review explores several animal models that provide insights into IgAN pathogenesis, emphasizing the roles of aberrant IgA1 glycosylation and immune complex formation. It discusses spontaneous, immunization, and transgenic models illustrating unique aspects of IgAN development and progression. The animal models, represented by the grouped ddY (gddY) mouse, have provided guidance concerning the multi-hit pathogenesis of IgAN. In this paradigm, genetic and environmental factors, including the dysregulation of the mucosal immune system, lead to increased levels of aberrantly glycosylated IgA, nephritogenic immune complex formation, and subsequent glomerular deposition, followed by mesangial cell activation and injury. Additionally, this review considers the implications of clinical trials targeting molecular pathways influenced by IgAN (e.g., a proliferation-inducing ligand [APRIL]). Collectively, these animal models have expanded the understanding of IgAN pathogenesis while facilitating the development of therapeutic strategies that are currently under clinical investigation. Animal-model-based studies have the potential to facilitate the development of targeted therapies with reduced side effects for IgAN patients.

Identification of IgA autoantibodies targeting mesangial cells redefines the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis, often progressing to renal failure. IgAN is triggered by IgA deposition in the glomerular mesangium by an undefined mechanism. Here, we show that grouped ddY (gddY) mice, a spontaneous IgAN model, produce serum IgA against mesangial antigens, including βII-spectrin. Most patients with IgAN also have serum anti-βII-spectrin IgA. As in patients with IgAN, IgA⁺ plasmablasts accumulate in the kidneys of gddY mice. IgA antibodies cloned from the plasmablasts carry substantial V-region mutations and bind to βII-spectrin and the surface of mesangial cells. These IgAs recognize transfected and endogenous βII-spectrin exposed on the surface of embryonic kidney-derived cells. Last, we demonstrate that the cloned IgA can bind selectively to glomerular mesangial regions in situ. The identification of IgA autoantibody and its antigen in IgAN provides key insights into disease onset and redefines IgAN as a tissue-specific autoimmune disease.

IgA vasculitis with transient glomerular hematuria, diarrhea, and pericarditis following COVID-19 mRNA vaccination in a young patient with possible pre-existing ulcerative colitis

Exacerbations or de novo autoimmune/autoinflammatory disease have been reported after COVID-19 vaccination. A young male presented with cutaneous IgA vasculitis with glomerular hematuria, diarrhea and pericarditis following his second COVID-19 mRNA vaccination. He also showed positivity for proteinase 3 anti-neutrophil cytoplasmic antibody (PR3-ANCA) and anti-cardiolipin antibody. Skin biopsy was compatible to IgA vasculitis. His purpura subsided and hematuria spontaneously disappeared. Treatment with anti-inflammatory medications and prednisolone resolved the pericarditis. He had a history of persistent diarrhea, and colonic biopsies showed possible ulcerative colitis without vasculitis. Kidney biopsy after prednisolone therapy revealed minor glomerular abnormalities without any immune reactants and did not show vasculitis. After prednisolone treatment, PR3-ANCA decreased in a medium degree despite of improvement of symptoms and inflammatory data, suggesting that his PR3-ANCA may be associated with ulcerative colitis. The cause of the transient glomerular hematuria was unclear, however, it might be caused by focal glomerular active lesions (glomerular vasculitis) due to vaccine-induced IgA vasculitis with nephritis. This case highlights that COVID-19 mRNA vaccination can activate multiple autoimmune/autoinflammatory systems. The conditions might help us better understand the mutual mechanisms of the relevant disorders.

Mucosal Immune System Dysregulation in the Pathogenesis of IgA Nephropathy

The mucosal immune system, via a dynamic immune network, serves as the first line of defense against exogenous antigens. Mucosal immune system dysregulation is closely associated with the pathogenesis of immunoglobulin A nephropathy (IgAN), as illustrated by IgAN having the clinical feature of gross hematuria, often concurrent with mucosal infections. Notably, previous studies have demonstrated the efficacy of tonsillectomy and found that a targeted-release formulation of budesonide reduced proteinuria in patients with IgAN. However, it remains unclear how exogenous antigens interact with the mucosal immune system to induce or exacerbate IgAN. Thus, in this review, we focus on the dysregulation of mucosal immune response in the pathogenesis of IgAN.

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

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

Glomerular deposition of galactose-deficient IgA1-containing immune complexes via glomerular endothelial cell injuries

BACKGROUND

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of IgA nephropathy (IgAN). However, the pathological role of Gd-IgA1-containing immune complexes (ICs) and the mechanism of deposition in the mesangial region remain unclear.

METHODS

To examine deposition of Gd-IgA1-containing ICs in the mesangial region through glomerular endothelial cell injury, we evaluated the alteration of renal microvascular endothelial glycocalyx in nude mice injected with Gd-IgA1-IgG ICs. Human renal glomerular endothelial cells (HRGECs) were used to assess the potential capacity of Gd-IgA1-IgG ICs to activate endothelial cells.

RESULTS

Nude mice injected with Gd-IgA1-containing ICs showed podocyte and endothelial cell injuries with IgA, IgG, and C3 depositions in glomerular capillaries and the mesangium. Moreover, albuminuria and hematuria were induced. Real-time glycocalyx imaging showed that renal microvascular glycocalyx was decreased immediately after injection of Gd-IgA1-containing ICs and then mesangial IgA deposition was increased. After coculture of Gd-IgA1-containing ICs with HRGECs, mRNA expression levels of endothelial adhesion molecules and proinflammatory mediators were upregulated significantly.

CONCLUSION

Gd-IgA1-IgG ICs had a high affinity for glomerular endothelial cells, which resulted in glomerular filtration barrier dysfunction mediated by glycocalyx loss. Furthermore, Gd-IgA1-IgG ICs accelerated production of adhesion factors and proinflammatory cytokines in glomerular endothelial cells. The glomerular endothelial cell injury induced by Gd-IgA1-containing ICs may enhance the permeability of immunoglobulins in the mesangial region and subsequent inflammatory responses in the pathogenesis of IgAN.

Galactose-Deficient IgA1 as a Candidate Urinary Marker of IgA Nephropathy

In patients with IgA nephropathy (IgAN), circulatory IgA1 and IgA1 in the mesangial deposits contain galactose-deficient IgA1 (Gd-IgA1). Some of the Gd-IgA1 from the glomerular deposits is excreted in the urine and thus urinary Gd-IgA1 may represent a disease-specific marker. We recruited 338 Japanese biopsy-proven IgAN patients and 120 patients with other renal diseases (disease controls). Urine samples collected at the time of renal biopsy were used to measure Gd-IgA1 levels using a specific monoclonal antibody (KM55 mAb). Urinary Gd-IgA1 levels were significantly higher in patients with IgAN than in disease controls. Moreover, urinary Gd-IgA1 was significantly correlated with the severity of the histopathological parameters in IgAN patients. Next, we validated the use of urinary Gd-IgA1 levels in the other Asian cohorts. In the Korean cohort, urinary Gd-IgA1 levels were also higher in patients with IgAN than in disease controls. Even in Japanese patients with IgAN and trace proteinuria (less than 0.3 g/gCr), urinary Gd-IgA1 was detected. Thus, urinary Gd-IgA1 may be an early disease-specific biomarker useful for determining the disease activity of IgAN.

IgA nephropathy with glomerular capillary IgA deposition following SARS-CoV-2 mRNA vaccination: a report of three cases

IgA nephropathy (IgAN) cases histopathologically showing glomerular capillary IgA deposition represent a rare subtype of primary IgAN. Patients with IgAN categorized to this subtype often exhibit heavy proteinuria, advanced histological findings, and are resistant to therapies. Here, we report three cases of biopsy-proven IgAN with glomerular capillary IgA deposition who presented acute deterioration of urinalysis findings following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccinations. Case 1 was recurrent IgAN. Case 2 and Case 3 were newly diagnosed cases with subclinical microhematuria and proteinuria history. All three cases showed gross hematuria and acute exacerbations of proteinuria following SARS-CoV-2 mRNA vaccinations. In all three cases, kidney biopsy findings showed IgA deposition in glomerular capillary walls in addition to mesangial and para-mesangial areas; acute glomerular lesions, such as intra- and extracapillary proliferations were identified, indicating the possibility of a potentially severe type of IgAN. Therefore, attention should be paid to patients with de novo or relapsing IgAN showing marked capillary IgA deposition following SARS-CoV-2 vaccination.

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.

Glomerular endothelial activation, C4d deposits and microangiopathy in immunoglobulin A nephropathy

Immunoglobulin A nephropathy (IgAN) is considered as mesangiopathy since it initiates in the mesangium; however, other glomerular components are involved and the glomerular capillary wall offers the first contact to circulating macromolecular IgA1. Acute and active forms of IgAN are associated with endocapillary hypercellularity and vascular damage of various degrees, in severe cases with microangiopathy (MA) without or with thrombosis [thrombotic microangiopathy (TMA)]. Vascular damage activates complement and coagulation cascades. A defective complement regulation has recently been detected in active and progressive cases of IgAN. C4d deposits in renal biopsies have been found to be an early risk factor. These observations have raised interest in manifestation of MA and TMA in progressive cases of IgAN. MA-TMA lesions have been found in various percentages (2-53%) of patients with IgAN according to patients' selection and pathology definition of TMA. The association with hypertension (HTN) was so strong that it led to the hypothesis that MA/TMA in IgAN was a mere consequence of severe HTN. Old and new clinical and experimental data indicate that in IgAN the interaction of the glomerular capillary wall with immune reactants and complement uncontrolled activation leading to C4b deposits favours the development of MA-TMA, which plays a role in progression and renal function decline. The central role of complement activation is relevant also for the new therapeutic interventions offered by the pharma.

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.

Clinicopathological significance of glomerular capillary IgA deposition in childhood IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is characterized by predominant mesangial IgA deposition. Some patients with IgAN demonstrate IgA deposition in glomerular peripheral capillaries (cap-IgA). The clinicopathological significance of cap-IgA remains incompletely investigated in children.

METHODS

We retrospectively analyzed 503 consecutive cases of biopsy-proven childhood IgAN between July 1976 and June 2013 to compare clinical and pathological features between IgAN patients with and without cap-IgA.

RESULTS

Among the 503 patients, 30 (6.0%) had cap-IgA. We found significant differences in proteinuria (2.0 vs. 0.5 g/day/m², p < 0.0001), time from onset to kidney biopsy (2.2 vs. 8.3 months, p < 0.0001), and rate of proteinuria remission after treatment (23.3% vs. 48.0%, p = 0.007) between both groups. Pathological analysis revealed significant differences in M1 (83.3% vs. 56.0%, p = 0.002), ratio of subendothelial electron dense deposits (EDDs, 58.6% vs. 16.5%, p < 0.0001) and subepithelial EDDs (48.3% vs. 16.5%, p = 0.0001), and glomerular basement membrane (GBM) lysis (58.6% vs. 27.1%, p = 0.0006) between both groups. More than half of cap-IgA patients (17/30, 56.7%), whereas only 26.2% of non-cap-IgA patients (124/473), were treated with immunosuppressive treatments. Six of 30 cases (20%) with cap-IgA reached glomerular filtration rate (GFR) categories G3a-G5 (estimated GFR < 60 ml/min/1.73 m²) at most recent observation (mean observation period: 7.0 ± 4.0 years). According to Kaplan-Meier analysis, patients with cap-IgA had significantly lower kidney survival curves than non-cap-IgA patients (72.8% vs. 97.2% at 10 years, p < 0.0001).

CONCLUSIONS

Cap-IgA is associated with acute inflammation with GBM changes, resulting in refractory heavier proteinuria. Cap-IgA may represent a poor prognostic factor.

Transcriptomic and Proteomic Profiling Provides Insight into Mesangial Cell Function in IgA Nephropathy

IgA nephropathy (IgAN), the most common GN worldwide, is characterized by circulating galactose-deficient IgA (gd-IgA) that forms immune complexes. The immune complexes are deposited in the glomerular mesangium, leading to inflammation and loss of renal function, but the complete pathophysiology of the disease is not understood. Using an integrated global transcriptomic and proteomic profiling approach, we investigated the role of the mesangium in the onset and progression of IgAN. Global gene expression was investigated by microarray analysis of the glomerular compartment of renal biopsy specimens from patients with IgAN (n=19) and controls (n=22). Using curated glomerular cell type-specific genes from the published literature, we found differential expression of a much higher percentage of mesangial cell-positive standard genes than podocyte-positive standard genes in IgAN. Principal coordinate analysis of expression data revealed clear separation of patient and control samples on the basis of mesangial but not podocyte cell-positive standard genes. Additionally, patient clinical parameters (serum creatinine values and eGFRs) significantly correlated with Z scores derived from the expression profile of mesangial cell-positive standard genes. Among patients grouped according to Oxford MEST score, patients with segmental glomerulosclerosis had a significantly higher mesangial cell-positive standard gene Z score than patients without segmental glomerulosclerosis. By investigating mesangial cell proteomics and glomerular transcriptomics, we identified 22 common pathways induced in mesangial cells by gd-IgA, most of which mediate inflammation. The genes, proteins, and corresponding pathways identified provide novel insights into the pathophysiologic mechanisms leading to IgAN.

Galactose-Deficient IgA1 as a Candidate Urinary Polypeptide Marker of IgA Nephropathy?

In patients with IgA nephropathy (IgAN), circulatory IgA1 and IgA1 in mesangial deposits contain elevated amounts of galactose-deficient IgA1 (Gd-IgA1). We hypothesized that a fraction of Gd-IgA1 from the glomerular deposits and/or circulation may be excreted into the urine and thus represent a disease-specific biomarker. Levels of urinary IgA and Gd-IgA1 were determined in 207 patients with IgAN, 205 patients with other renal diseases, and 57 healthy controls, recruited in USA, Japan, and Italy. Urinary IgA was similarly elevated in patients with IgAN and renal-disease controls compared with healthy controls. However, urinary Gd-IgA1 levels were higher in patients with IgAN (IgAN, 28.0 ± 17.9; disease controls, 20.6 ± 17.4 units/mg urinary creatinine; P < 0.0001). Lectin western blotting data confirmed these results. In IgAN patients, levels of urinary Gd-IgA1 correlated with proteinuria (P < 0.001). When we purified IgA from serum and urine of an IgAN patient, the relative proportion of Gd-IgA1 to total IgA1 was higher in the urine compared with serum, suggesting selective excretion of Gd-IgA1 in IgAN. In summary, urinary excretion of Gd-IgA1 was elevated in patients with IgAN and the urinary Gd-IgA1 levels correlated with proteinuria. Urinary Gd-IgA1 may thus represent a disease-specific biomarker of IgAN.