Association Between Galactose-Deficient IgA1 Derived From the Tonsils and Recurrence of IgA Nephropathy in Patients Who Underwent Kidney Transplantation

Pathogenic Immunoglobulin A-Producing Cells in Immunoglobulin A Nephropathy

Immunoglobulin A nephropathy (IgAN) is the most prevalent primary glomerular disease worldwide and it remains a leading cause of kidney failure. Clinical manifestations of IgA are exacerbated by infections, and emerging data suggest that aberrant mucosal immune responses are important contributors to the immunopathogenesis of this disease. However, the exact stimuli, location and mechanism of nephritis-inducing IgA production remains unclear. In this focused review we explore recent developments in our understanding of the contribution of the mucosal immune system and mucosal-derived IgA-producing cells to the development of IgAN.

Accelerated involution of germinal center in palatine tonsils in IgA nephropathy

BACKGROUND

Altered immunological responses in the palatine tonsils may be involved in the pathogenesis of IgA nephropathy (IgAN). The germinal center serves as the site for antigen-specific humoral immune responses in the palatine tonsils. Germinal center involution is frequently observed in the palatine tonsils of IgAN (IgAN tonsils). However, the pathogenic significance of these characteristic changes remains unclear. This study aimed to investigate the morphological changes in secondary lymphoid follicles in IgAN tonsils and to evaluate the correlation between the morphometric results and the clinicopathological severity of IgAN.

METHODS

The tonsils of age-matched patients with recurrent tonsillitis (RT tonsils) were used as controls. The correlation between the degree of lymphoid follicular involution and histopathological severities in clinical or kidney biopsy was evaluated.

RESULTS

In total, 87 patients with IgAN were included (48% male, median age 35 years, median estimated glomerular filtration rate: 74 mL/min/1.73 m2). Compared to RT tonsils, IgAN tonsils showed smaller median sizes of lymphoid follicles and germinal centers (P < 0.001). The relative areas of lymphoid follicles (%LFA) and germinal centers (%GCA) in the total tonsillar tissue were smaller in the IgAN tonsils than in the RT tonsils (P < 0.001). In contrast, the median proportion of mantle zones in the total tonsillar tissue was comparable between the groups. A lower %LFA was associated with a longer period from the onset of urinary abnormalities to biopsy diagnosis and higher urinary protein excretion (P = 0.01). %LFA showed significant negative correlations with frequencies of glomeruli with both global and segmental sclerosis.

CONCLUSIONS

The present study confirmed accelerated germinal center involution in the tonsils of patients with IgAN. This characteristic change in the IgAN tonsil correlates with heavy proteinuria and advanced chronic histopathological changes in the kidneys, thereby suggesting the involvement of repeated tonsillar immunoreactions during IgAN progression.

Ethnicity and IgA nephropathy: worldwide differences in epidemiology, timing of diagnosis, clinical manifestations, management and prognosis

Immunoglobulin A nephropathy (IgAN), the most common primary glomerulonephritis, is one of the major causes of end-stage renal disease. Significant variances in epidemiology, clinical manifestation, timing of diagnosis, management and renal prognosis of IgAN have been reported worldwide. The incidence of IgAN is the most frequent in Asia, followed by Europe, and lower in Africa. Moreover, Asian patients show more frequent acute lesions in renal histology and present poorer renal outcomes compared with Caucasians. The comorbidities also show the difference between Asians and Caucasians. Although the frequency of gross hematuria with upper respiratory tract infection is not different, comorbidities with gastrointestinal diseases are reported to be higher in Europe. Recently, genetic studies for variant ethnic patients revealed widely ranging genetic risks in each ethnicity. A genetic risk score is most elevated in Asians, intermediate in Europeans and lowest in Africans, consistent with the disease prevalence of IgAN globally. Ethnic variance might be highly affected by the difference in genetic background. However, it is also essential to mention that the different timing of diagnosis due to variant urinary screening systems and the indication for renal biopsy in different countries may also contribute to these variances. The management of IgAN also varies internationally. Currently, several novel therapies based on the pathogenesis of IgAN are being assessed and are expected to become available soon. Further understanding the ethnic variance of IgAN might help establish individualized care for this disease. Here, we review the issues of ethnic heterogeneities of IgAN.

IgA nephropathy

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

Acute exacerbation of immunoglobulin A nephropathy complicated by alveolar hemorrhage after coronavirus disease 2019 vaccination: A case report

RATIONALE

Reports have suggested a relationship between coronavirus disease 2019 (COVID-19) vaccination and new-onset or recurring renal diseases, of which immunoglobulin A (IgA) nephropathy is a representative disease. Alveolar hemorrhage in patients with IgA nephropathy is rare but reportedly has a high mortality and morbidity. To our knowledge, there have been no reports regarding the development of IgA nephropathy with alveolar hemorrhage following COVID-19 vaccination.

PATIENTS CONCERN

A 23-year-old Japanese man presented with hemoptysis and peripheral edema a few days after receiving a second dose of a COVID-19 mRNA vaccine. Severe renal failure and alveolar hemorrhage were noted thereafter, and renal biopsy showed crescentic glomerulonephritis with mesangial proliferation accompanied by mesangial electron-dense deposits containing IgA. Renal biopsy tissue also showed chronic histological changes suggestive of acute exacerbation of preexisting IgA nephropathy.

DIAGNOSIS

The diagnosis of IgA nephropathy complicated by alveolar hemorrhage was made.

INTERVENTIONS AND OUTCOMES

Renal function did not recover despite treatment with high-dose steroids; the patient was maintained on hemodialysis and eventually underwent successful renal transplantation.

LESSONS

The present case suggested that although extremely rare, severe renal failure requiring renal replacement therapy could occur in patients with IgA nephropathy after COVID-19 vaccination. Future accumulation of similar cases is needed to predict the risk of renal injury following vaccination.

Associations of corticosteroid therapy and tonsillectomy with kidney survival in a multicenter prospective study for IgA nephropathy

Efficacy of systemic corticosteroid therapy (CS) for long-term kidney survival in patients with IgA nephropathy (IgAN) is controversial. Therefore, prospective studies evaluating targeted therapies to lymphatic tissues in mucosal immune system responsible for production of nephritogenic IgA have been desired worldwide. Here, we aimed to evaluate the associations of CS and combination therapy of CS and tonsillectomy (CS + Tx) with kidney survival, using database from a nationwide multicenter prospective cohort study on IgAN. Primary outcome was a 50% increase in serum creatinine from baseline or dialysis induction. The analysis included 941 patients (CS/CS + Tx/non-CS 239/364/338), 85 (9.0%) of whom reached outcomes during median follow-up of 5.5 (interquartile range 2.0-8.0) years. On overlap weighting analysis with balanced baseline characteristics, CS and CS + Tx were associated with lower risk of kidney events when compared with non-CS (hazard ratio [HR] 0.51, 95% confidence interval [CI] 0.29-0.88 and HR 0.20, 95%CI 0.09-0.44, respectively). Notably, when compared with the CS, CS + Tx was associated with a lower risk of kidney events (HR 0.40, 95%CI 0.18-0.91). Present study demonstrated, keeping with favorable association of systemic CS with kidney survival, concurrent tonsillectomy as one of targeted interventions to lymphatic tissues may provide additional improvement to kidney survival in patients with IgAN.

Serum galactose-deficient immunoglobulin A1 in recurrent immunoglobulin a nephropathy after kidney transplantation: A meta-analysis

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is a main cause of end stage renal disease (ESRD). Many IgAN patients with ESRD accept kidney allograft for renal replacement. However, disease recurrence occurs after transplantation. Galactose-deficient immunoglobulin A1(Gd-IgA1) has been proved to be a crucial biomarker in the primary IgAN population.

METHODS

This meta-analysis aimed to explore the association between serum Gd-IgA1 and IgAN recurrence after renal transplantation and was registered on PROSPERO: CRD42022356952; A literature search was performed and relevant studies were retrieved from the PubMed, Embase and Cochrane library databases from inception to April 27, 2023. The inclusion criteria were: 1) full-text studies; 2) patients with histological diagnosis of IgAN of their native kidneys who underwent kidney transplantation; 3) studies exploring the relationship between serum Gd-IgA1 and IgAN recurrence after kidney transplantation. The exclusion criteria were: 1) reviews, case reports, or non-clinical studies. 2) studies with insufficient original data or incomplete data. 3) studies with duplicated data. Study quality was assessed using Newcastle Ottawa Scale (NOS). Data were pooled using a random-effects model.

RESULTS

8 full-text studies including 515 patients were identified. The Newcastle-Ottawa Scale (NOS) score ranged from 6 to 8. The standard mean difference (SMD) of the level of Gd-IgA1 was significantly higher in recurrence group than in non-recurrence group (SMD = 0.50，95%CI = 0.15-0.85, p = 0.005). Furthermore, Gd-IgA1 levels were higher in recurrence patients than in non-recurrence in both Europe subgroup (SMD 0.45, 95%CI: 0.08-0.82, p = 0.02) and Asia subgroup (SMD 0.90, 95%CI: 0.10-1.70, p = 0.03). However, pretransplant Gd-IgA1 levels showed no significant difference between recurrence and non-recurrence group (SMD 0.46, 95%CI: 0.06-0.99, p = 0.08) in anther subgroup analysis while posttransplant Gd-IgA1 levels were significantly higher in recurrence population than in non-recurrence (SMD 0.57, 95%CI 0.21 to 0.92, p = 0.002).

CONCLUSIONS

This meta-analysis showed that posttransplant serum Gd-IgA1 levels are associated with IgAN recurrence after kidney transplantation; however, pretransplant serum Gd-IgA1 levels are not.

Clinical and Pathological Significance of Mesangial C1q Deposition in Kidney Transplant Recipients with Recurrent IgA Nephropathy and Patients with Native IgA Nephropathy

INTRODUCTION

In kidney transplant recipients (KTRs) whose primary disease is IgA nephropathy (IgAN), IgAN recurrence occurs in approximately half of patients by 5 years postoperatively and is associated with graft survival. Although the alternative and lectin pathways are important in the primary pathogenesis of IgAN, the significance of mesangial C1q deposition, which triggers the classical pathway, is unknown. We investigated the clinicopathological significance of mesangial C1q deposition in both recurrent IgAN in KTRs and native IgAN.

METHODS

Between 2000 and 2021, we conducted a 1:2 matched case-control study of 18 KTRs diagnosed with recurrent IgAN, with a group of native IgAN patients as the control. We evaluated the rate and presence/absence of mesangial C1q deposition in terms of pathological findings and kidney outcomes in each group.

RESULTS

The rate of mesangial C1q deposition was significantly higher in the recurrent IgAN patients in KTRs than in native IgAN patients (11/18 [61.1%] vs. 5/36 [13.9%], p = 0.001). In the former group, the incidence of glomerular crescents was relatively higher in C1q-positive patients. There was no significant difference in the annual rate of estimated glomerular filtration rate decline between C1q-positive and C1q-negative patients in either group.

CONCLUSION

Mesangial C1q deposition was more frequent in KTRs with recurrent IgAN than in patients with native IgAN, but we found no difference in kidney outcomes with respect to mesangial C1q deposition. Further large-scale investigations of the importance of mesangial C1q deposition are needed in both KTRs with recurrent IgAN and patients with native IgAN.

Early Recurrence of Immunoglobulin A Nephropathy after Kidney Transplantation in a Patient with Down Syndrome

A 39-year-old male kidney transplant recipient with Down syndrome (DS) was admitted to our hospital for biopsy. He had proteinuria at age 9, was diagnosed with immunoglobulin A nephropathy (IgAN) at age 22, had a tonsillectomy at age 35, and underwent ABO-compatible kidney transplantation (from his mother) at age 36. His serum creatinine was stable at 2.21 mg/dL 3 months after the kidney transplant, and his urine protein was 0.11 g/day. A protocol biopsy was performed 7 months after the kidney transplant, and there was suspicion of early recurrence of IgAN. One year after the transplant, urine erythrocytes were elevated and proteinuria was 0.41 g/day; at 3 years and 5 months after the kidney transplant, hematuria was evident along with proteinuria (0.74 g/day). Therefore, an episode biopsy was performed. A total of 23 glomeruli were obtained, four of which exhibited global sclerosis; three others showed intra- and extracapillary proliferative glomerulonephritis compatible with IgAN recurrence. Here, we report a rare case of early recurrence of IgAN with disease progression despite tonsillectomy in a patient with DS.

Current Status and Perspectives on Recurrent IgA Nephropathy after Kidney Transplantation

IgA nephropathy (IgAN) is the most common form of glomerulonephritis worldwide. IgAN progresses to end-stage kidney disease in 20-40% of patients within 20 years of diagnosis. Kidney transplantation is the most effective option for patients with end-stage kidney disease caused by IgAN, but recurrence can occur in the transplanted kidney. The IgAN recurrence rate varies from 1% to 10% per year and varies according to the follow-up period, diagnostic modality, and biopsy criteria. Of note, studies based on protocol biopsies have reported a higher incidence of recurrence, which also occurred earlier after transplantation. In addition, recent data show that recurrence of IgAN is a more significant cause of allograft failure than previously believed. Little is known about the pathophysiology of IgAN recurrence, but several potential biomarkers have been investigated. Among them, galactose-deficient IgA1 (Gd-IgA1), IgG anti-Gd-IgA1 antibodies, and soluble CD89 could play a pivotal role in disease activity. This review aims to describe the current status of recurrent IgAN, including the incidence, clinical characteristics, risk factors, and future perspectives, with a focus on the available therapeutic approaches.

Aberrant Gut Microbiome Contributes to Barrier Dysfunction, Inflammation, and Local Immune Responses in IgA Nephropathy

INTRODUCTION

Numerous research works have shown that serum Gal-deficient (Gd) IgA1 levels are increased in IgA nephropathy (IgAN) patients and these levels are a dangerous risk factor for IgAN. A relationship between the gut microbiota and IgAN has been reported. Whether the gut microbiota participates in the pathogenesis of IgAN was still controversial.

METHODS

We evaluated changes in the gut flora and the levels of Gd-IgA1 in IgAN patients and healthy controls (HCs). We investigated the Gd-IgA1 levels in both blood and urine specimens. C57BL/6 mice were given a broad-spectrum antibiotic cocktail to deplete the endogenous gut flora. We established a model of IgAN in pseudosterile mice and investigated the expression of the markers of intestinal permeability, inflammation, and local immune responses.

RESULTS

Studies have shown that the levels of certain gut flora differ between IgAN patients and HCs. Moreover, elevated Gd-IgA1 levels were found in both the serum and urine. Interestingly, Coprococcus, Dorea, Bifidobacterium, Blautia, and Lactococcus, selected from 10 candidate biomarkers to predict risk in IgAN patients according to random forest analysis, were inversely associated with urinary Gd-IgA1 levels. Notably, the urine level of Gd-IgA1 could best distinguish IgAN patients from HCs. Additionally, the degree of kidney damage in pseudosterile mice with IgAN was more severe than that in mice with IgAN. Furthermore, the markers of intestinal permeability were significantly elevated in pseudosterile IgAN mice. Moreover, the inflammation responses (TLR4, MyD88, and NF-κB in intestinal and renal tissues; TNF-α and IL-6 in serum) and local immune responses (BAFF and APRIL in intestinal tissue) were upregulated in pseudosterile IgAN mice.

CONCLUSIONS

The urine Gd-IgA1 level may be as a biomarker for the early screening of potential IgAN, and gut microbiota dysbiosis was demonstrated in IgAN, which might involve the dysfunction of the mucosal barrier, inflammation, and local immune responses.

IgA Nephropathy: Current Understanding and Perspectives on Pathogenesis and Targeted Treatment

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, with varied clinical and histopathological features between individuals, particularly across races. As an autoimmune disease, IgAN arises from consequences of increased circulating levels of galactose-deficient IgA1 and mesangial deposition of IgA-containing immune complexes, which are recognized as key events in the widely accepted "multi-hit" pathogenesis of IgAN. The emerging evidence further provides insights into the role of genes, environment, mucosal immunity and complement system. These developments are paralleled by the increasing availability of diagnostic tools, potential biomarkers and therapeutic agents. In this review, we summarize current evidence and outline novel findings in the prognosis, clinical trials and translational research from the updated perspectives of IgAN pathogenesis.

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.

Antibody-Mediated Rejection and Recurrent Primary Disease: Two Main Obstacles in Abdominal Kidney, Liver, and Pancreas Transplants

The advances in acute phase care have firmly established the practice of organ transplantation in the last several decades. Then, the next issues that loom large in the field of transplantation include antibody-mediated rejection (ABMR) and recurrent primary disease. Acute ABMR is a daunting hurdle in the performance of organ transplantation. The recent progress in desensitization and preoperative monitoring of donor-specific antibodies enables us to increase positive outcomes. However, chronic active ABMR is one of the most significant problems we currently face. On the other hand, recurrent primary disease is problematic for many recipients. Notably, some recipients, unfortunately, lost their vital organs due to this recurrence. Although some progress has been achieved in these two areas, many other factors remain largely obscure. In this review, these two topics will be discussed in light of recent discoveries.

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

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