Deficiency of N-acetylgalactosamine in O-linked oligosaccharides of IgA is a novel biologic marker for Crohn's disease

Insights into renal and urological complications of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic condition characterized by immune-mediated inflammation in the gastrointestinal tract, which follows a relapsing and remitting course. Apart from affecting the gastrointestinal tract, IBD also has extra-intestinal manifestations (EIMs). While the etiology of extraintestinal manifestation remains unclear, it is theorized to be based on immunological responses influenced by genetic factors. Renal involvement is one of the EIMs observed in ulcerative colitis and Crohn's disease. The renal manifestations in IBD patients encompass a range of conditions including nephrolithiasis, amyloidosis, tubulointerstitial nephritis, glomerulonephritis (GN), obstructive pathologies, and chronic kidney disease (CKD). The incidence of CKD in IBD patients varies from 5%-15%. The decline in renal function can stem from various factors such as direct inflammatory damage to the kidneys leading to glomerular or tubular injury, or from complications like recurrent stones, amyloidosis, or GN. Additionally, nephrotoxic medications used in treating IBD, such as TNF-α inhibitors, calcineurin inhibitors, and aminosalicylates, can exacerbate the decline in renal function. Currently, there is a lack of consensus regarding these patients' screening and renal function monitoring. This review aims to assess the existing literature on the different renal complications among individuals with IBD, shedding light on their pathophysiology and management.

Association of Inflammatory Bowel Disease with Incident IgA Nephropathy

Key Points

We analyzed a nationwide epidemiologic cohort including approximately 4,000,000 individuals. We found a potential association of inflammatory bowel disease with a greater risk of developing IgA nephropathy.

Background

There have been scarce epidemiologic data on the relationship between inflammatory bowel disease and the incidence of IgA nephropathy. In this study, we assessed whether inflammatory bowel disease was associated with a higher risk of developing IgA nephropathy using a large-scale epidemiologic cohort.

Methods

We retrospectively analyzed 4,311,393 adults enrolled in the JMDC Claims Database (previously known as the Japan Medical Data Center database), a nationwide epidemiologic database in Japan. The definitions of IgA nephropathy and inflammatory bowel disease (ulcerative colitis or Crohn disease) were based on International Classification of Diseases, 10th Revision codes. Individuals who had a history of IgA nephropathy were excluded. Study participants were categorized into two groups according to the presence of inflammatory bowel disease. Clinical outcomes were collected between January 2005 and May 2022. The primary outcome was incident IgA nephropathy.

Results

Median (interquartile range) age was 44 (36–53) years, and 2,497,313 (58%) were men. Inflammatory bowel disease was observed in 18,623 individuals (0.4%). Over a median follow-up of 1089 (532–1797) days, there were 2631 incidences of IgA nephropathy and 22 incidences in individuals without and with inflammatory bowel disease, yielding incident ratios with 95% confidence intervals of 1.74 (1.68–1.81) and 3.43 (2.26–5.21), respectively. Kaplan–Meier curves and the log-rank test showed that a cumulative incidence of IgA was higher in individuals with inflammatory bowel disease compared with those without (log-rank P = 0.0028). Multivariable Cox regression analysis demonstrated that individuals with inflammatory bowel disease were at higher risk of incident IgA nephropathy (hazard ratio, 1.96; 95% confidence interval, 1.29 to 2.99).

Conclusions

We demonstrated the potential association of inflammatory bowel disease with higher risk of developing IgA nephropathy in a general population.

Kidney Diseases Associated With Inflammatory Bowel Disease: Impact of Chronic Histologic Damage, Treatments, and Outcomes

INTRODUCTION

Kidney disease is a well-known extraintestinal manifestation (EIM) associated with inflammatory bowel disease (IBD), with a variety of underlying etiologies. However, little is known about the overall outcomes and predictors.

METHODS

This is a retrospective, observational cohort study. Patients with IBD in whom a native kidney biopsy was performed at Mayo Clinic (Rochester, MN) between 1994 and 2022, were included. Demographic, clinical, and histologic characteristics of prognostic interest were collected. The main outcomes were kidney failure, disease remission, kidney function changes at last follow-up, and death.

RESULTS

From a total cohort of 318 patients, we selected a study group of 111 patients followed-up with at our institution (45 ulcerative colitis [UC] and 66 Crohn's disease [CD]), with a mean age of 48 ± 17 years (40% females). IgA nephropathy (IgAN), chronic interstitial nephritis (CIN), and acute interstitial nephritis (AIN) were the most common diagnoses (22%, 19%, 13%, respectively). Median estimated glomerular filtration rate (eGFR) at presentation was 30 ml/min per 1.73 m2 (interquartile range [IQR]: 17-54) and urinary protein-to-creatinine ratio [UPCR] 0.8 g/g (0.3-3.4), without differences between IBD types. During a median follow-up of 59 months (12-109), 29 patients (26%) reached kidney failure. By multivariable analysis, the main predictors of kidney failure were age (hazard ratio [HR]: 1.04; P = 0.002), baseline eGFR (HR: 0.94; P = 0.003) and histologic chronicity score (HR: 4.01; P < 0.001). Therapeutic management varied according to underlying etiology. Global survival (kidney failure + death) was significantly better in patients who achieved complete or partial remission, or stabilization or improvement of kidney function.

CONCLUSION

One-fourth of patients with IBD with kidney disease may reach kidney failure, and the main determinants of this outcome is age, baseline eGFR, and degree of chronicity in kidney biopsy.

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.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Racial heterogeneity of IgA1 hinge-region O-glycoforms in patients with IgA nephropathy

Galactose (Gal)-deficient IgA1 (Gd-IgA1) is involved in IgA nephropathy (IgAN) pathogenesis. To reflect racial differences in clinical characteristics, we assessed disease- and race-specific heterogeneity in the O-glycosylation of the IgA1 hinge region (HR). We determined serum Gd-IgA1 levels in Caucasians (healthy controls [HCs], n = 31; IgAN patients, n = 63) and Asians (HCs, n = 20; IgAN patients, n = 60) and analyzed profiles of serum IgA1 HR O-glycoforms. Elevated serum Gd-IgA1 levels and reduced number of Gal residues per HR were observed in Caucasians. Reduced number of N-acetylgalactosamine (GalNAc) residues per HR and elevated relative abundance of IgA1 with three HR O-glycans were common features in IgAN patients; these features were associated with elevated blood pressure and reduced renal function. We speculate that the mechanisms underlying the reduced GalNAc content in IgA1 HR may be relevant to IgAN pathogenesis.

Causal association between inflammatory bowel disease and IgA nephropathy: A bidirectional two-sample Mendelian randomization study

Background: An association between inflammatory bowel disease (IBD) [which includes ulcerative colitis (UC) and Crohn's disease (CD)] and IgA nephropathy (IgAN) has been discovered in observational studies, but the causal relationship is still unknown. The aim of this study was to clarify the causal link between IBD (which includes UC and CD) and IgAN via a two-sample Mendelian randomization (MR) analysis. Methods: Eligible single-nucleotide polymorphisms (SNPs) were selected as instrumental variables (IVs) for analyses and were obtained from the publicly available genome-wide association study (GWAS) summary statistics. Inverse-variance weighting (IVW), Mendelian randomization-Egger (MR-Egger) regression, the Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) test, and the weighted median were utilized to obtain the results. The MR-PRESSO test and MR-Egger regression were also performed to detect and correct horizontal pleiotropy. The Cochran's Q test and "leave-one-out" analysis were also conducted to assess the stability and reliability of the MR results. Results: This study found that IBD, UC, and CD all had significant positive causal effects on IgAN risk (IBD: OR = 1.58, 95% CI 1.15-2.16, p = 4.53 × 10-3; UC: OR = 1.55, 95% CI 1.14-2.11, p = 4.88 × 10-3; CD: OR = 1.57, 95% CI 1.21-2.03, p = 5.97 × 10-4). No significant horizontal pleiotropic effect was found for the causal association between IBD, UC, CD, and the risk of IgAN. Cochran's Q test identified no evidence of heterogeneity for the IV estimates. The "leave-one-out" sensitivity analysis also revealed that the MR results were robust. Conclusion: The results of this two-sample MR analysis supported that IBD, UC, and CD were causally associated with the risk of IgAN, while there was no sufficient evidence for the causal effect of IgAN on IBD, UC, or CD. Our findings provide theoretical support and a new perspective for the diagnosis and treatment of these two diseases.

Advances in IgA glycosylation and its correlation with diseases

Immunoglobulin A (IgA) is the most abundant immunoglobulin synthesized in the human body. It has the highest concentration in the mucosa and is second only to IgG in serum. IgA plays an important role in mucosal immunity, and is the predominant antibody used to protect the mucosal surface from pathogens invasion and to maintain the homeostasis of intestinal flora. Moreover, The binding IgA to the FcαRI (Fc alpha Receptor I) in soluble or aggregated form can mediate anti- or pro- inflammatory responses, respectively. IgA is also known as one of the most heavily glycosylated antibodies among human immunoglobulins. The glycosylation of IgA has been shown to have a significant effect on its immune function. Variation in the glycoform of IgA is often the main characteration of autoimmune diseases such as IgA nephropathy (IgAN), IgA vasculitis (IgAV), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). However, compared with the confirmed glycosylation function of IgG, the pathogenic mechanism of IgA glycosylation involved in related diseases is still unclear. This paper mainly summarizes the recent reports on IgA’s glycan structure, its function, its relationship with the occurrence and development of diseases, and the potential application of glycoengineered IgA in clinical antibody therapeutics, in order to provide a potential reference for future research in this field.

Diagnostic Potential of Plasma IgA1 O-Glycans in Discriminating IgA Nephropathy From Other Glomerular Diseases and Healthy Participants

Background: Aberrant O-glycosylation of IgA1 plays an important role in IgA nephropathy pathogenesis. Previous proteomic studies analyzed O-glycans of the circulating IgA1 hinge region and found that the N-acetylgalactosamine (GalNAc) and galactose numbers in the hinge region of IgA1 of patients with IgA nephropathy were lower than those in healthy participants. However, the diagnostic performance of the O-glycosylation traits in the hinge region of plasma IgA1 for IgA nephropathy remains unelucidated. The present study aimed to determine the difference in plasma IgA1 hinge region O-glycoforms among IgA nephropathy, non-IgA nephropathy disease controls, and healthy participants, and to further evaluate the diagnostic performance of plasma IgA1 glycosylation traits.

Methods: Sixty-two patients with biopsy-proven primary IgA nephropathy, 30 age- and sex-matched non-IgA nephropathy disease controls (10 patients with membranous nephropathy, 10 with focal segmental glomerulosclerosis, and 10 with minimal change disease), and 30 healthy participants were prospectively recruited. Plasma galactose deficient-IgA1 levels were measured using a KM55 kit. Plasma IgA was extracted using IgA immunoaffinity beads. After de-N-glycosylation, reduction, alkylation, trypsin digestion, and O-glycopeptide enrichment via hydrophilic interaction liquid chromatography, liquid chromatography tandem mass spectrometry (LC-MS/MS) was applied to analyze the IgA1 O-glycosylation patterns and we derived the plasma IgA1 O-glycosylation traits.

Results: Plasma IgA1 O-glycosylation patterns were significantly changed in IgA nephropathy patients compared to those with non-IgA nephropathy disease controls and healthy participants. The GalNAc number was lowest in IgA nephropathy patients. In addition, a similar result was observed for the galactose number in the IgA1 hinge region. These values showed moderate potential for discriminating between IgA nephropathy and the controls. When these values were combined, the area under the curve increased compared to when they were considered individually. When further adding a clinical indicator, the area under the curve of the GalNAc-galactose-IgA panel exceed 0.9 in discriminating IgA nephropathy from the controls.

Conclusion: The amount of GalNAc and galactose in plasma IgA1 hinge region identified by glycoproteomics could be used as a diagnostic biomarker for IgA nephropathy. The panel containing GalNAc, galactose, and circulating IgA displayed excellent diagnostic performance and is promising for practical clinical applications.

Small intestinal bacterial overgrowth in patients with inflammatory bowel disease: A case-control study

BACKGROUND

Though small intestinal bacterial overgrowth (SIBO) is known in inflammatory bowel disease (IBD), the data on it are scanty and have limitations.

METHODS

Data on IBD patients undergoing glucose hydrogen breath test (GHBT) were retrospectively analyzed to evaluate the frequency and risk factors of SIBO in IBD compared to 66 healthy controls.

RESULTS

Patients with IBD (n=86; 45 ulcerative colitis [UC] and 41 Crohn's disease [CD]) more often had SIBO on GHBT than the healthy subjects (16/86 [18.6%] vs. 1/66 [1.5%]; p=0.002). SIBO was commoner among patients with CD than UC (14/41 [34.1%] vs. 2/45 [4.4%]; p=0.001). The frequency of SIBO among UC patients was comparable to healthy subjects (2/45 [4.4%] vs. 1/66 [1.5%]; p=not significant [NS]). Patients with CD than those with UC had higher values of maximum breath hydrogen and a greater area under the curve for breath hydrogen. Other factors associated with SIBO included female gender (11/16 [68.8%] with vs. 21/70 [30%] without SIBO; p=0.003), and having undergone surgery (8/16 [50%] vs. 6/70 [8.6%]; p=0.0002). SIBO patients had lower levels of total serum protein and albumin than those without SIBO (6.2 ± 1.5 g/dL vs. 7.0 ± 0.9 g/dL, respectively; p=0.009 and 3.5 ± 0.9 g/dL vs. 4.0 ± 0.6 g/dL, respectively; p=0.02). CD, female gender, and surgery for IBD tended to be the independent factors associated with SIBO among IBD patients on multivariate analysis.

CONCLUSIONS

Patients with IBD, particularly CD, female, and those having undergone surgery, have a higher risk of SIBO than the healthy controls.

Title IgA Nephropathy and Oral Bacterial Species Related to Dental Caries and Periodontitis

A relationship between IgA nephropathy (IgAN) and bacterial infection has been suspected. As IgAN is a chronic disease, bacteria that could cause chronic infection in oral areas might be pathogenetic bacteria candidates. Oral bacterial species related to dental caries and periodontitis should be candidates because these bacteria are well known to be pathogenic in chronic dental disease. Recently, several reports have indicated that collagen-binding protein (cnm)-(+) Streptococcs mutans is relate to the incidence of IgAN and the progression of IgAN. Among periodontal bacteria, Treponema denticola, Porphyromonas gingivalis and Campylobacte rectus were found to be related to the incidence of IgAN. These bacteria can cause IgAN-like histological findings in animal models. While the connection between oral bacterial infection, such as infection with S. mutans and periodontal bacteria, and the incidence of IgAN remains unclear, these bacterial infections might cause aberrantly glycosylated IgA1 in nasopharynx-associated lymphoid tissue, which has been reported to cause IgA deposition in mesangial areas in glomeruli, probably through the alteration of microRNAs related to the expression of glycosylation enzymes. The roles of other factors related to the incidence and progression of IgA, such as genes and cigarette smoking, can also be explained from the perspective of the relationship between these factors and oral bacteria. This review summarizes the relationship between IgAN and oral bacteria, such as cnm-(+) S. mutans and periodontal bacteria.

IgA Vasculitis in Patients with Inflammatory Bowel Disease: new insights into the role of TNF-α blockers

OBJECTIVE

Association of IgA vasculitis (IgAV) and inflammatory bowel diseases (IBD) is rarely described, mainly during anti-TNF-α therapy. We aimed to describe the association of IgAV and IBD.

METHODS

We retrospectively analyzed the association of IgAV and IBD through the implication of the GETAID and FVSG networks. Characteristics of IBD and IgAV were collected using a standardized case report form.

RESULTS

Forty-three cases were included. IBD (mainly Crohn's disease (CD) in 58%) preceded IgAV in 38 (88%), with median interval of 9.2 (IQR 5.4-15.4) years. In these 38 patients, at IgAV diagnosis, 5 (13%) had active IBD and 28 (74%) were treated with anti-TNF-α for a median duration of 31.5 (IQR 19-56) months. Main IgAV manifestations were purpura all patients (100%), joints in 20/35 (57%), renal in 15/35 (43%) and gastrointestinal in 11/35 (31%) involvement. IgAV was treated with glucocorticoids in 25 (66%), colchicine in 6 (16%), cyclophosphamide in 6 (16%), and anti-TNF-α were discontinued in 15/28 (54%). No IgAV relapse occurred when TNF-α blockers were stopped, vs 23% in patients pursuing it. Conversely, 5 (33%) had IBD flare or complication after anti-TNF-α cessation vs 1 (8%) in those continuing biologics. Anti-TNF-α were resumed in 6 (40%), with subsequent IgAV relapse in 4 (67%).

CONCLUSIONS

This large cohort suggests that TNF-α blockers may promote the onset of IgAV in IBD. Discontinuation of anti-TNF-α was associated with vasculitis remission but increased risk of IBD relapses, whereas continuation of anti-TNF-α was associated with IBD remission but vasculitis relapse.

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

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

Nasal-associated lymphoid tissue is the major induction site for nephritogenic IgA in murine IgA nephropathy

Dysregulation of mucosal immunity may play a role in the pathogenesis of IgA nephropathy (IgAN). However, it is unclear whether the nasal-associated lymphoid tissue (NALT) or gut-associated lymphatic tissue is the major induction site of nephritogenic IgA synthesis. To examine whether exogenous mucosal antigens exacerbate the pathogenesis of IgAN, we assessed the disease phenotypes of IgAN-onset ddY mice housed germ-free. These mice were transferred to a specific pathogen-free environment and divided into three groups: challenged with the Toll-like receptor 9 (TLR9) ligand CpG-oligodeoxynucleotide, fecal transplantation, and the untreated control group. The levels of aberrantly glycosylated IgA and IgG-IgA immune complexes were measured in the serum and supernatant of cultured cells purified from the NALT, mesenteric lymph nodes, and Peyer's patch. Although the germ-free IgAN-onset ddY mice did not develop IgAN, they showed aggravation of kidney injury with mesangial IgA deposition after transfer to the specific pathogen-free state. The NALT cells produced more aberrantly glycosylated IgA than those from the mesenteric lymph node and Peyer's patch, resulting in induction of IgG-IgA immune complexes formation. Additionally, TLR9 enhanced the production of nephritogenic IgA and IgG-IgA immune complexes by nasal-associated lymphoid but not gut-associated lymphatic cells. Furthermore, the germ-free IgAN-onset ddY mice nasally immunized with CpG-oligonucleotide showed aggravation of kidney injury with mesangial IgA deposition, whereas those that received fecal transplants did not develop IgAN. Thus, NALT is the major induction site of the production of aberrantly glycosylated IgA in murine IgAN.

IgA nephropathy in association with inflammatory bowel diseases: results from a national study and systematic literature review

BACKGROUND

Little is known about clinical characteristics and kidney outcome in patients with biopsy-proven immunoglobulin A nephropathy (IgAN) in a context of inflammatory bowel disease (IBD).

METHODS

We conducted a retrospective multicenter study with centralized histological review, to analyze the presentation, therapeutic management and outcome of 24 patients suffering from IBD associated IgAN relative to a cohort of 134 patients with primary IgAN without IBD.

RESULTS

Crohn's disease and ulcerative colitis accounted for 75% and 25% of IBD-associated IgAN cases, respectively. IBD was diagnosed before IgAN in 23 cases (a mean of 9 years previously) and was considered active at IgAN onset in 23.6% of patients. Hypertension was present in 41.7% of patients. Urinary protein-to-creatinine ratio exceeded 100 mg/mmol in 70.8% of patients (mean: 254 mg/mmol). Estimated glomerular filtration rate (eGFR) exceeded 60 ml/min/1.73m2 in 13/24 patients and only one patient required dialysis. In the Oxford MEST-C classification of renal biopsies, 57% were M1, 48% E1, 76% S1, 57% T1+T2 and 38% C1+C2. Steroids were administered in 50% of cases. After a mean follow-up of 7.2 years, four patients (16.7%) had a poor kidney outcome: end-stage renal disease (n = 3) or a > 50% decrease in eGFR from initial values (n = 1). A similar evolution was observed in patients with primitive IgAN.

CONCLUSIONS

This first case series suggests that IBD-associated IgAN have frequent inflammatory lesions at onset and variable long-term outcome.

Immunoglobulin A Glycosylation and Its Role in Disease

Human IgA is comprised of two subclasses, IgA1 and IgA2. Monomeric IgA (mIgA), polymeric IgA (pIgA), and secretory IgA (SIgA) are the main molecular forms of IgA. The production of IgA rivals all other immunoglobulin isotypes. The large quantities of IgA reflect the fundamental roles it plays in immune defense, protecting vulnerable mucosal surfaces against invading pathogens. SIgA dominates mucosal surfaces, whereas IgA in circulation is predominately monomeric. All forms of IgA are glycosylated, and the glycans significantly influence its various roles, including antigen binding and the antibody effector functions, mediated by the Fab and Fc portions, respectively. In contrast to its protective role, the aberrant glycosylation of IgA1 has been implicated in the pathogenesis of autoimmune diseases, such as IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAVN). Furthermore, detailed characterization of IgA glycosylation, including its diverse range of heterogeneity, is of emerging interest. We provide an overview of the glycosylation observed for each subclass and molecular form of IgA as well as the range of heterogeneity for each site of glycosylation. In many ways, the role of IgA glycosylation is in its early stages of being elucidated. This chapter provides an overview of the current knowledge and research directions.

N-glycome signatures in human plasma: associations with physiology and major diseases

N-glycome analysis in total plasma or serum yields information about the levels and glycosylation patterns of major plasma glycoproteins, including immunoglobulins, acute-phase proteins, and apolipoproteins. Until recently, glycomic studies in disease settings largely suffered from small cohort sizes, poor analytical resolution, and poor comparability of results owing to the diversity of analytical techniques. Here, we report on recent advances in high-throughput mass spectrometry glycomics technology that enabled elucidation of N-glycome signatures in the plasma of patients with type 2 diabetes, inflammatory bowel disease, or colorectal cancer. Use of this technology revealed both commonalities and differences among disease fingerprints. Moreover, we summarize findings on glycomic signatures associated with age, sex, and body mass index. High-throughput, high-resolution glycomics technologies, together with robust data analysis workflows, will advance clinical translation.

A novel pathogenesis of inflammatory bowel disease from the perspective of glyco-immunology

Oligosaccharide modifications play an essential role in various inflammatory diseases and cancers, but their pathophysiologic roles, especially in inflammation, are not clear. Inflammatory bowel disease (IBD) is an intractable chronic inflammatory disorder with an unknown aetiology, and the number of patients with IBD is increasing throughout the world. Certain types of immunosuppressant drugs, such as corticosteroids, are effective for IBD, suggesting that immune function is closely associated with the pathophysiology of IBD. Recent progress in the analysis of oligosaccharides revealed a role for oligosaccharides in intestinal inflammation based on both experimental models and human samples from IBD patients. Moreover, changes in the oligosaccharide structures on glycoproteins in the sera and tissue samples may serve as biomarkers of IBD. Here, we present current studies of IBD with regard to the immunologic aspects of glycobiology, suggesting a novel concept for IBD pathogenesis and the function of oligosaccharides on immune cells, termed "glyco-immunology".

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Emerging Biomarkers for the Diagnosis and Monitoring of Inflammatory Bowel Diseases

There is currently no single test available to confidently diagnose cases of inflammatory bowel disease (IBD). Physicians rely on a number of diagnostic tools, including clinical evaluation, serum testing, and imaging, which are used on conjunction with endoscopic evaluation. It is often difficult to determine whether patients with abdominal pain and change in bowel habit have functional bowel symptoms or whether they have a true diagnosis of IBD. Even once a diagnosis of IBD has been made, a significant proportion of patients are labeled with the term "indeterminate colitis" where histological sampling cannot confidently subclassify patients as either Crohn's or ulcerative colitis. Colonoscopy is an inconvenient and uncomfortable test for most patients. In addition, it is not without serious risks of perforation, as well as risks which can be associated with sedation and analgesia given during the procedure. The use of biomarkers to aid in the diagnosis, subclassification, and monitoring of IBD is an ever expanding area. In this review, we have concentrated on noninvasive biomarkers of IBD, because these are more acceptable to patients and easier to perform in everyday clinical practice. We will first touch on those biomarkers currently well established and in wide clinical use, such as C-reactive protein, erythrocyte sedimentation rate. Faecal calprotectin and their use in the diagnosis of IBD. Following on, we will review more novel biomarkers and their use in subclassification and monitoring of IBD, including a variety of antibodies, genetics, and microRNAs, as well as touching on metabolomics.

The role of glycosylation in IBD

A number of genetic and immunological studies give impetus for investigating the role of glycosylation in IBD. Experimental mouse models have helped to delineate the role of glycosylation in intestinal mucins and to explore the putative pathogenic role of glycosylation in colitis. These experiments have been extended to human studies investigating the glycosylation patterns of intestinal mucins as well as levels of glycans of serum glycoproteins and expression of glycan receptors. These early human studies have generated interesting hypotheses regarding the pathogenic role of glycans in IBD, but have generally been restricted to fairly small underpowered studies. Decreased glycosylation has been observed in the intestinal mucus of patients with IBD, suggesting that a defective inner mucus layer might lead to increased bacterial contact with the epithelium, potentially triggering inflammation. In sera, decreased galactosylation of IgG has been suggested as a diagnostic marker for IBD. Advances in glycoprofiling technology make it technically feasible and affordable to perform high-throughput glycan pattern analyses and to build on previous work investigating a much wider range of glycan parameters in large numbers of patients.

Lectin-reactive anti-α-gal in patients with Crohn's disease: correlation with clinical phenotypes

BACKGROUND

Patients with inflammatory bowel disease have higher proportions of immunoglobulin G (IgG) antibodies lacking N-galactose, also called agalactosyl IgG, in their serum. Such agalactosyl IgGs have been associated with disease activity and the immunogenicity of biologics. The aim was to describe the relationship between circulating levels of a subset of agalactosyl IgGs (anti-α-Gal) and Crohn's disease (CD) phenotypes.

METHODS

Prospectively collected serum samples of a well-characterized cohort of patients with inflammatory bowel disease and controls were used. Serum anti-α-Gal levels were measured by a high-affinity enzyme-linked immunosorbent assay and referenced to a standard control.

RESULTS

Serum samples from 167 subjects were tested; 62 with CD, 76 with ulcerative colitis, and 29 controls. Agalactosyl anti-α-Gal levels were significantly higher in active CD than in active ulcerative colitis (P = 0.0043) or healthy controls (P < 0.0001). Among patients with CD, agalactosyl anti-α-Gal levels were significantly higher in those with a history of arthritis, than those without (P = 0.0002), but lower in those taking immunomodulators (P = 0.03). There was no correlation between agalactosyl anti-α-Gal levels and indices of Crohn's severity, including C-reactive protein levels or Harvey-Bradshaw index. Patients who were primary or secondary nonresponders to infliximab had similar agalactosyl anti-α-Gal levels to clinical responders.

CONCLUSIONS

Patients with CD have greater amounts of agalactosylated anti-α-Gal antibodies in their serum, particularly in those with associated joint disease. This increase seems to be independent of indices of disease activity, but is influenced by immunomodulator use.

Quantitative change of IgA hinge O-glycan composition is a novel marker of therapeutic responses of IgA nephropathy

Aberrant O-glycosylation in the hinge region of serum IgA is suggested to be involved in the pathogenesis of IgA nephropathy (IgAN), because the hypoglycosylation including N-acetylneuraminic acid or galactose has been reported in the mucin-type O-glycan of the hinge portion (HP) of IgA deposited in the IgAN patients' kidney. These aberrant glycosylation has been assessed in most of the previous reports by qualitative but not quantitative methods. In the present study, the molar ratios of GalNAc or Gal to HP were analyzed for serum IgA from IgAN patients. The GalNAc/HP ratio was increased in the patients who achieved remission after a combination therapy of tonsillectomy and intravenous corticosteroid, suggesting any non-innate factors to affect the IgA O-glycosylation in IgAN that is thought to be inherently determined. Furthermore, the O-glycosylation status was different among three groups: IgAN patients in the pretreatment stage, IgAN patients in the remission stage after treatment and healthy controls. These results indicated that aberrant O-glycosylation of serum IgA in the IgAN patients would be inherently present and, to some extent, affected by therapeutic intervention. Finally, the quantitative change of O-glycan composition is a novel marker of therapeutic response of IgAN.