Identification of susceptibility locus shared by IgA nephropathy and inflammatory bowel disease in a Chinese Han population

Novel immune cross-talk between inflammatory bowel disease and IgA nephropathy

The mechanisms underlying the complex correlation between immunoglobulin A nephropathy (IgAN) and inflammatory bowel disease (IBD) remain unclear. This study aimed to identify the optimal cross-talk genes, potential pathways, and mutual immune-infiltrating microenvironments between IBD and IgAN to elucidate the linkage between patients with IBD and IgAN. The IgAN and IBD datasets were obtained from the Gene Expression Omnibus (GEO). Three algorithms, CIBERSORTx, ssGSEA, and xCell, were used to evaluate the similarities in the infiltrating microenvironment between the two diseases. Weighted gene co-expression network analysis (WGCNA) was implemented in the IBD dataset to identify the major immune infiltration modules, and the Boruta algorithm, RFE algorithm, and LASSO regression were applied to filter the cross-talk genes. Next, multiple machine learning models were applied to confirm the optimal cross-talk genes. Finally, the relevant findings were validated using histology and immunohistochemistry analysis of IBD mice. Immune infiltration analysis showed no significant differences between IBD and IgAN samples in most immune cells. The three algorithms identified 10 diagnostic genes, MAPK3, NFKB1, FDX1, EPHX2, SYNPO, KDF1, METTL7A, RIDA, HSDL2, and RIPK2; FDX1 and NFKB1 were enhanced in the kidney of IBD mice. Kyoto Encyclopedia of Genes and Genomes analysis showed 15 mutual pathways between the two diseases, with lipid metabolism playing a vital role in the cross-talk. Our findings offer insights into the shared immune mechanisms of IgAN and IBD. These common pathways, diagnostic cross-talk genes, and cell-mediated abnormal immunity may inform further experimental studies.

Inflammatory Bowel Disease With Chronic Kidney Disease and Acute Kidney Injury

INTRODUCTION

It remains unclear whether inflammatory bowel disease is associated with long-term risk of chronic kidney disease (CKD) and acute kidney injury (AKI) in the general population.

METHODS

A total of 417,302 participants, including 2,940 patients with ulcerative colitis and 1,261 patients with Crohn's disease, without previous CKD and AKI at baseline (2006-2010) from the UK Biobank were included. The study outcomes included incident CKD and AKI, ascertained by self-report data and data linkage with primary care, hospital admissions, and death registry records. Analysis was conducted in 2022.

RESULTS

During a median follow-up of 12.5 years, 13,564 and 14,331 participants developed CKD and AKI, respectively. Compared with the hazard ratio for non-inflammatory bowel diseases, the hazard ratios for CKD and AKI related to inflammatory bowel diseases were 1.57 (95% CI=1.37, 1.79) and 1.96 (95% CI=1.74, 2.20) after adjustments for age, sex, and race and were 1.32 (95% CI=1.15, 1.51) and 1.70 (95% CI=1.51, 1.91) after further adjustments for biological, behavioral, and socioeconomic factors in addition to mental health and self-rated health. Similar results were found for patients with Crohn's disease (adjusted hazard ratio=1.38 (95% CI=1.09, 1.75) for CKD and 1.62 [95% CI=1.30, 2.02] for AKI) and those with ulcerative colitis (adjusted hazard ratio=1.29 (95% CI=1.09, 1.51) for CKD and 1.71 [95% CI=1.49, 1.97] for AKI) in the fully adjusted models. Genetic risks of kidney diseases did not significantly affect the association of inflammatory bowel disease with incident CKD and AKI (both p-interactions>0.05). The association between inflammatory bowel disease and the risk of incident CKD (p-interaction=0.010) and AKI (p-interaction<0.001) were stronger in younger participants than in older participants.

CONCLUSIONS

Inflammatory bowel disease was associated with higher risks for CKD and AKI, independent of genetic risks of kidney diseases.

Immunoglobulin A Glycosylation Differs between Crohn's Disease and Ulcerative Colitis

Inflammatory bowel diseases (IBD), such as Crohn's disease (CD) and ulcerative colitis (UC), are chronic and relapsing inflammations of the digestive tract with increasing prevalence, yet they have unknown origins or cure. CD and UC have similar symptoms but respond differently to surgery and medication. Current diagnostic tools often involve invasive procedures, while laboratory markers for patient stratification are lacking. Large glycomic studies of immunoglobulin G and total plasma glycosylation have shown biomarker potential in IBD and could help determine disease mechanisms and therapeutic treatment choice. Hitherto, the glycosylation signatures of plasma immunoglobulin A, an important immunoglobulin secreted into the intestinal mucin, have remained undetermined in the context of IBD. Our study investigated the associations of immunoglobulin A1 and A2 glycosylation with IBD in 442 IBD cases (188 CD and 254 UC) and 120 healthy controls by reversed-phase liquid chromatography electrospray-ionization mass spectrometry of tryptic glycopeptides. Differences of IgA O- and N-glycosylation (including galactosylation, bisection, sialylation, and antennarity) between patient groups were associated with the diseases, and these findings led to the construction of a statistical model to predict the disease group of the patients without the need of invasive procedures. This study expands the current knowledge about CD and UC and could help in the development of noninvasive biomarkers and better patient care.

Analysis of the interferon-γ-induced secretome of intestinal endothelial cells: putative impact on epithelial barrier dysfunction in IBD

The development of inflammatory bowel diseases (IBD) involves the breakdown of two barriers: the epithelial barrier and the gut-vascular barrier (GVB). The destabilization of each barrier can promote initiation and progression of the disease. Interestingly, first evidence is available that both barriers are communicating through secreted factors that may accordingly serve as targets for therapeutic modulation of barrier functions. Interferon (IFN)-γ is among the major pathogenesis factors in IBD and can severely impair both barriers. In order to identify factors transmitting signals from the GVB to the epithelial cell barrier, we analyzed the secretome of IFN-γ-treated human intestinal endothelial cells (HIEC). To this goal, HIEC were isolated in high purity from normal colon tissues. HIEC were either untreated or stimulated with IFN-γ (10 U/mL). After 48 h, conditioned media (CM) were harvested and subjected to comparative hyper reaction monitoring mass spectrometry (HRM™ MS). In total, 1,084 human proteins were detected in the HIEC-CM. Among these, 43 proteins were present in significantly different concentrations between the CM of IFN-γ- and control-stimulated HIEC. Several of these proteins were also differentially expressed in various murine colitis models as compared to healthy animals supporting the relevance of these proteins secreted by inflammatory activated HIEC in the inter-barrier communication in IBD. The angiocrine pathogenic impact of these differentially secreted HIEC proteins on the epithelial cell barrier and their perspectives as targets to treat IBD by modulation of trans-barrier communication is discussed in detail.

Glomerulonephritis and inflammatory bowel disease: A tale of gut-kidney axis dysfunction

The incidence and prevalence of Inflammatory Bowel Disease (IBD) has increased over the past decades, imposing a growing socioeconomic burden on healthcare systems globally. Most of the morbidity and mortality related to IBD is typically attributed to gut inflammation and its complications; yet the disease is characterized by various extraintestinal manifestations that can be severe. Glomerulonephritis (GN) is of particular interest since a significant proportion of patients evolve into end-stage kidney disease, requiring kidney replacement therapy and associated with high morbidity and mortality. Herein, we review the GN landscape in IBD and define the clinical and pathogenic associations reported to date in the literature. Underlying pathogenic mechanisms suggest either the initiation of antigen-specific immune responses in the inflamed gut that cross react with non-intestinal sites, such as the glomerulus, or that extraintestinal manifestations are gut-independent events that occur due to an interaction between common genetic and environmental risk factors. We present data associating GN with IBD either as a bona fide extraintestinal manifestation or reporting it as an extraneous co-existing entity, involving various histological subtypes, such as focal segmental glomerulosclerosis, proliferative GN, minimal change disease, crescentic GN, but most emphatically IgA nephropathy. Supporting the pathogenic interplay between gut inflammation and intrinsic glomerular processes, enteric targeting the intestinal mucosa with budesonide reduced IgA nephropathy-mediated proteinuria. Elucidating the mechanisms at play would provide insight not only into IBD pathogenesis but also into the gut's role in the development of extraintestinal diseases, such as glomerular diseases.

Functional variant rs12614 in CFB confers a low risk of IgA nephropathy by attenuating complement alternative pathway activation in Han Chinese

Activation of the alternative pathway (AP) of complement is thought to play an important role in Immunoglobin A nephropathy (IgAN). Our previous study showed that rs4151657 within the complement factor B (CFB) gene increased the risk of IgAN. The protein encoded by the CFB gene is an initial factor that promotes AP activation. The aim of this study was to investigate whether other variants of CFB confer susceptibility to IgAN and elucidate their potential roles in AP activation. A total of 1,350 patients with IgAN and 1,420 healthy controls were enrolled and five tag single-nucleotide polymorphisms were selected for genotyping. The levels of key AP components, such as CFB, complement factor H and complement split product C3a, were measured by enzyme-linked immunosorbent assay. Molecular docking and molecular dynamic simulation were carried out to characterize the mutation of residues in the protein structure and the dynamic properties of wide type and mutation models of CFB protein. The allele-specific effect on CFB expression and its binding affinity to C3b were investigated through cell transfection and surface plasmon resonance analysis, respectively. We found that rs12614 significantly reduced the risk of IgAN (OR = 0.69, 95% CI = 0.52-0.91, P = 0.009), and the rs12614-T (R32W mutation) was correlated with lower CFB levels, higher serum C3 level, and less mesangial C3 deposition in patients with IgAN. The structural model showed that the R32W mutation reduced the structural stability of CFB protein. Furthermore, in vitro study revealed that rs12614-T decreased the expression of CFB and reduced its binding affinity to C3b by four-fold compared with rs12614-C. In conclusion, the rs12614-T in CFB was associated with low risk of IgAN probably by attenuating AP activation.

The Gut and Kidney Crosstalk in Immunoglobulin A Nephropathy

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

Renal manifestations in inflammatory bowel disease: a systematic review

As extra-intestinal manifestations (EIMs) are frequent in inflammatory bowel disease (IBD) and affect morbidity and sometimes even mortality, vigilance in the surveillance of EIMs and installing the appropriate treatment are essential. Data on renal manifestations in patients with IBD are however rare. Nevertheless, up to 5-15% of adult patients with IBD will develop chronic kidney disease over time. The pathophysiology of renal involvement in patients with IBD is complex and poorly understood, with a wide range of renal disorders affecting the glomeruli and/or the tubular structure. Furthermore, medication used to treat IBD can be potentially nephrotoxic and metabolic complication due to the disease itself can furthermore cause renal damage. The aim of this systematic review is to provide an overview of the existing data in literature on these renal manifestations and complications in patients with IBD.

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.

Single-cell RNA-sequencing reveals distinct immune cell subsets and signaling pathways in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common primary glomerulonephritis globally. Increasing evidence suggests the importance of host immunity in the development of IgAN, but its dynamics during the early stage of IgAN are still largely unclear.

RESULTS

Here we successfully resolved the early transcriptomic changes in immune cells of IgAN by conducting single-cell RNA-sequencing (scRNA-seq) with peripheral blood mononuclear cells. The differentially expressed genes (DEGs) between control and IgAN were predominantly enriched in NK cell-mediated cytotoxicity and cell killing pathways. Interestingly, we discovered that the number and cytotoxicity of NK cells are significantly reduced in IgAN patients, where both the number and marker genes of NK cells were negatively associated with the clinical parameters, including the levels of urine protein creatinine ratio (UPCR), serum galactose-deficient IgA1 and IgA. A distinctive B cell subset, which had suppressed NFκB signaling was predominantly in IgAN and positively associated with disease progression. Moreover, the DEGs of B cells were enriched in different viral infection pathways. Classical monocytes also significantly changed in IgAN and a monocyte subset expressing interferon-induced genes was positively associated with the clinical severity of IgAN. Finally, we identified vast dynamics in intercellular communications in IgAN.

CONCLUSIONS

We dissected the immune landscape of IgAN at the single-cell resolution, which provides new insights in developing novel biomarkers and immunotherapy against glomerulonephritis.

Role of gut-kidney axis in renal diseases and IgA nephropathy

PURPOSE OF REVIEW

Growing evidence show the importance of gut/kidney axis in renal diseases. Advances in gut microbiome sequencing, associated metabolites, detection of gut permeability and inflammation provide new therapeutic strategies targeting gut for kidney diseases and particularly for Immunoglobulin A (IgA) nephropathy (IgAN).

RECENT FINDINGS

The diversity and composition of gut flora have been recently deeply explored in kidney diseases. Modulation and depletion of microbiota in animal models allowed the understanding of molecular mechanisms involved in the crosstalk between gut, immune system and kidney. New clinical trials in order to positively modulate microbiota result in improvement of gastrointestinal disorders and inflammation in patients suffering with kidney diseases.

SUMMARY

The investigation of gut alterations in kidney diseases open new therapeutic strategies. In IgAN, targeted treatments for intestinal inflammation and modifications of gut microbiota seem promising.

Serum complement factor B is associated with disease activity and progression of idiopathic membranous nephropathy concomitant with IgA nephropathy

PURPOSE

Few studies have reported the roles of the complement system in concomitant idiopathic membranous nephropathy and IgA nephropathy (IMN-IgAN). Complement factor B (CFB) is a crucial factor that involved in the alternative complement pathway. We aimed to evaluate the association between disease activity (eGFR, anti-PLA2R antibody levels and 24 h urinary protein excretion), progression and serum CFB levels of IMN-IgAN patients.

METHODS

In total, 39 IMN-IgAN patients (median follow-up, 46.6 months), 99 IMN patients and 92 IgAN patients participated in this study. The disease progression event was defined as end-stage renal disease (ESRD) or a 30% decline in estimated glomerular filtration rate (eGFR). The serum CFB concentration was measured by enzyme-linked immunosorbent assay.

RESULTS

Serum CFB levels were lower in IMN-IgAN patients than in patients with IgAN only (P < .001). Serum CFB levels correlated positively with serum creatinine levels, anti-PLA2R antibody levels and 24 h urinary protein excretion (P < .05). Kaplan-Meier analysis revealed that IMN-IgAN patients with high serum CFB levels had a significantly lower cumulative renal survival rate than patients with low levels (log-rank test, P = .009). Multivariate Cox regression analysis showed that high baseline serum CFB levels were significantly associated with poor renal outcome in patients with IMN-IgAN (HR: 2.727, 95% CI 1.076-6.913, P = .034).

CONCLUSION

High serum CFB levels correlated with increased serum creatinine, anti-PLA2R antibody and urinary protein excretion as well as poor renal prognosis in patients with IMN-IgAN, indicating that serum CFB may be a marker of disease activity and progression.

Association of Immune and Inflammatory Gene Polymorphism With the Risk of IgA Nephropathy: A Systematic Review and Meta-Analysis of 45 Studies

IgA nephropathy is the most prevalent primary glomerulonephritis worldwide, with identical immunopathological characteristics caused by multiple etiologies as well as influenced by geographical and ethnical factors. To elucidate the role of immunologic and inflammatory mechanisms in the susceptibility to IgA nephropathy, we explored single nucleotide polymorphisms of related molecules in the immune pathways. We searched the PubMed database for studies that involved all gene variants of molecules in the 20 immunologic and inflammatory pathways selected from the Kyoto Encyclopedia of Genes and Genomes database. The odds ratios with their corresponding 95% confidence intervals in six genetic models (allele model, dominant model, homozygote model, heterozygote model, overdominant model, and recessive model) were summarized using fixed or random effect models. Subgroup analysis was conducted based on different ethnicities with generalized odds ratios. Heterogeneity was evaluated using the Q and I² tests. Begg’s funnel plot and Egger’s linear regression test were used to evaluating possible publication bias among the included studies, and sensitivity analysis was used to test the stability of the overall results. A total of 45 studies met our selection criteria and eight related genetic association studies were retrieved, including 320 single-nucleotide polymorphisms from 20 candidate pathways, ranging from 2000 to 2021. A total of 28,994 healthy people versus 20,600 IgA nephropathy patients were enrolled. Upon meta-analyzed results that TGFB1 (rs1800469, rs1982073, rs1800471), IL-1B (rs1143627), IL-18 (rs1946518), and TLR1 (rs5743557) showed effect with or without ethnicity difference. And 10 variants presented stable and robust related to IgA nephropathy. This research showed that genetic variants are related to the immunologic and inflammatory effects of IgA nephropathy pathogenesis. The meta-analysis results supported the previous researches, and may help deepen the understanding of pathogenesis and explore new targets for IgA nephropathy-specific immunotherapy.

Exome Chip Analyses and Genetic Risk for IgA Nephropathy among Han Chinese

BACKGROUND AND OBJECTIVES

IgA nephropathy is the most common form of primary GN worldwide. The evidence of geographic and ethnic differences, as well as familial aggregation of the disease, supports a strong genetic contribution to IgA nephropathy. Evidence for genetic factors in IgA nephropathy comes also from genome-wide association patient-control studies. However, few studies have systematically evaluated the contribution of coding variation in IgA nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a two-stage exome chip-based association study in 13,242 samples, including 3363 patients with IgA nephropathy and 9879 healthy controls of Han Chinese ancestry. Common variant functional annotation, gene-based low-frequency variants analysis, differential mRNA expression, and gene network integration were also explored.

RESULTS

We identified three non-HLA gene regions (FBXL21, CCR6, and STAT3) and one HLA gene region (GABBR1) with suggestive significance (Pmeta <5×10-5) in single-variant associations. These novel non-HLA variants were annotated as expression-associated single-nucleotide polymorphisms and were located in enhancer regions enriched in histone marks H3K4me1 in primary B cells. Gene-based low-frequency variants analysis suggests CFB as another potential susceptibility gene. Further combined expression and network integration suggested that the five novel susceptibility genes, TGFBI, CCR6, STAT3, GABBR1, and CFB, were involved in IgA nephropathy.

CONCLUSIONS

Five novel gene regions with suggestive significance for IgA nephropathy were identified and shed new light for further mechanism investigation.

Inflammatory Bowel Disease Is More Common in Patients with IgA Nephropathy and Predicts Progression of ESKD: A Swedish Population-Based Cohort Study

BACKGROUND

Case reports suggest an association between inflammatory bowel disease, a chronic autoimmune condition linked to increased circulating IgA levels, and IgA nephropathy, the most common form of primary GN and a leading cause of ESKD.

METHODS

In a Swedish population-based cohort study, we compared 3963 biopsy-verified IgA nephropathy patients with 19,978 matched controls between 1974 and 2011, following up participants until 2015. Inflammatory bowel disease data and ESKD status were obtained through national medical registers. We applied Cox regression to estimate hazard ratios (HRs) for future inflammatory bowel disease in IgA nephropathy and conditional logistic regression to assess risk of earlier inflammatory bowel disease in IgA nephropathy. We also explored whether inflammatory bowel disease affects development of ESKD in IgA nephropathy.

RESULTS

During a median follow-up of 12.6 years, 196 (4.95%) patients with IgA nephropathy and 330 (1.65%) matched controls developed inflammatory bowel disease (adjusted HR, 3.29; 95% confidence interval [95% CI], 2.73 to 3.96). Inflammatory bowel disease also was more common before a confirmed IgA nephropathy diagnosis. Some 103 (2.53%) IgA nephropathy patients had an earlier inflammatory bowel disease diagnosis compared with 220 (1.09%) controls (odds ratio [OR], 2.37; 95% CI, 1.87 to 3.01). Both logistic regression (OR, 2.60; 95% CI, 2.02 to 3.35) and time-varying Cox regression (HR, 1.84; 95% CI, 1.33 to 2.55) demonstrated that inflammatory bowel disease was associated with increased ESKD risk in patients with IgA nephropathy.

CONCLUSIONS

Patients with IgA nephropathy have an increased risk of inflammatory bowel disease both before and after their nephropathy diagnosis. In addition, among patients with IgA nephropathy, comorbid inflammatory bowel disease elevates the risk of progression to ESKD.

Prevalence of Inflammatory Bowel Disease and Celiac Disease in Patients with IgA Nephropathy over Time

INTRODUCTION

IgA nephropathy (IgAN) has been connected with increased intestinal permeability and subclinical intestinal mucosal inflammation as well as with inflammatory bowel disease (IBD) and celiac disease - nevertheless, the results are controversial. The prevalence of bowel diseases has increased over time in Western populations. Whether similar trend is seen among IgAN patients remains obscure. Our aim was to study the prevalence of IBD and celiac disease in IgAN patients over time.

METHODS

The study cohort consisted of altogether 629 patients with newly diagnosed IgAN during years 1976-2012. Data on diagnosis of IBD and celiac disease were retrospectively collected from medical records. Further, to detect unrecognized celiac disease, IgA-class tissue transglutaminase antibodies (tTGA) were measured from serum samples taken at the time of kidney biopsy during years 1980-2012 (defined as screen-detected celiac disease autoimmunity).

RESULTS

The prevalence of IBD among IgAN patients increased over time from 0 to 4.4%, while the prevalence of clinically diagnosed celiac disease decreased from 2.6 to 0.6%. Moreover, the number of screen-detected tTGA-positive cases decreased from the 1980s to the 21st century (2.8-0.7%).

CONCLUSION

The prevalence of IBD increased over time in IgAN patients, which exceeds the prevalence of 0.6% in Finnish general population. In parallel, the prevalence of celiac disease and screen-detected celiac disease autoimmunity decreased over time. The coexistence of IBD and IgAN is not negligible. Whether this finding is caused by the increase in the prevalence of IBD in the population or shared pathophysiology between IgAN and IBD remains a matter of further studies.

IgA Nephropathy in the Setting of Anti-TNF-α Therapy for Inflammatory Bowel Disease

Tumor necrosis factor-α (TNF-α)-inhibiting agents are a standard therapy for moderate-to-severe inflammatory bowel disease (IBD). IgA nephropathy in the setting of prolonged exposure to TNF-α inhibitors is a rare, clinically significant adverse event often overlooked by gastroenterologists but well documented in the rheumatologic literature. We present a case series of 3 patients with IBD on TNF-α inhibitors who developed biopsy-proven IgA nephropathy. Clinicians prescribing TNF-α inhibitors to patients with IBD need to be aware of this potential side effect. Therapies with alternative mechanisms of action should instead be considered.