Enzymatically deglycosylated human IgA1 molecules accumulate and induce inflammatory cell reaction in rat glomeruli

Tetrandrine inhibits the proliferation of mesangial cells induced by enzymatically deglycosylated human IgA1 via IgA receptor/MAPK/NF-κB signaling pathway

Objective: Despite the use of renin-angiotensin system blockade and immunosuppressive drugs, including corticosteroids, the current treatment regimens for Immunoglobulins A nephropathy (IgAN) are severely limited. The proliferation of mesangial cell and deposition of deglycosylated human IgA1 immune complex are the most common pathologic features of IgAN. We examined the tetrandrine potential of suppressing the proliferation of mesangial cells and explored its underlying mechanisms with a focus on IgA receptor/MAPK/NF-κB signaling pathway. Methods: Standard human IgA (native IgA) were enzymatically desialylated (deS IgA) or further degalactosylated (deS/deGal IgA) using neuraminidase and β-galactosidase. Rat glomerular mesangial cells (HBZY-1) and human renal mesangial cells (HRMC) stimulated by IgA were used to observe the suppressive effect of tetrandrine. The MTT assay was used to detect the cell viability. The protein expression of IgA receptor/MAPK/NF-κB signaling pathway was examined by Western blot. Cell cycle analysis was measured by flow cytometer. Results: Native IgA and deS IgA showed limited stimulation effect on both HBZY-1 cells and HRMCs, whereas deS/deGal IgA significantly stimulated the proliferation of both HBZY-1 cells and HRMCs (p < 0.05). Compared with non-stimulation of deS/deGal IgA, 1-3 μM of tetrandrine had stronger inhibitory effect on the proliferation of HBZY-1 cells and HRMCs with the stimulation of deS/deGal IgA (p < 0.05), suggesting that tetrandrine possibly inhibited the proliferation of mesangial cells induced by deglycosylated human IgA1 specifically. Molecular mechanism study revealed that tetrandrine decreased the expression of IgA1 receptor, CD71 and β4GALT1, and inhibited the activation of MAPK/NF-κB significantly (p < 0.05). Moreover, these inhibitory effect of tetrandrine caused cell cycle arrest and stopped the cell growth in the S phase companied with the upregulating of cyclin A2 and downregulating of cyclin D1. Conclusion: Taken together, tetrandrine inhibited the proliferation of mesangial cells induced by enzymatically deglycosylated human IgA1 via IgA receptor/MAPK/NF-κB signaling pathway. Based on these potential molecular mechanisms, tetrandrine would be an appealing therapeutic option for IgAN.

Pregnancy after lung and heart-lung transplantation: a French multicentre retrospective study of 39 pregnancies

Pregnancy after lung and heart–lung transplantation remains rare. This French study deals with change in lung function after a pregnancy and the maternal and newborn outcomes.

We retrospectively included 39 pregnancies in 35 women aged >20 years. Data on patients, course of pregnancies and newborns were collected from nine transplantation centres.

Mean age at time of pregnancy was 28 years. Cystic fibrosis affected 71% of patients. Mean±sd time between transplantation and pregnancy was 63±44 months. 26 births occurred (67%) with a mean term of 36 weeks of amenorrhoea and a mean birthweight of 2409 g. Prematurity was observed in 11 cases (43%). Forced expiratory volume in 1 s was 83.9% of predicted before pregnancy and 77.3% of predicted 1 year after the end of pregnancy (p=0.04). 10 patients developed chronic lung allograft dysfunction after delivery. Nine patients died at a mean±sd time after transplantation of 8.2±7 years and a mean±sd time after pregnancy of 4.6±6.5 years.

These data show that pregnancy remains feasible in lung and heart–lung transplant recipients, with more frequent maternal and newborn complications than in the general population. Survival in this cohort appears to be similar to the global survival observed in lung transplant recipients. Planned pregnancy and multidisciplinary follow-up are crucial.

Pregnancy in lung and heart–lung recipients remains rare but possible. There is a significant decrease in FEV₁ pre- and post-pregnancy, but overall outcomes are reassuring. Specialised, multidisciplinary follow-up is necessary.http://bit.ly/31iXxov

Screening and prevention for latent tuberculosis in immunosuppressed patients at risk for tuberculosis: a systematic review of clinical practice guidelines

OBJECTIVE

Immunosuppressed individuals are at a high risk of latent tuberculosis infection (LTBI) and clinical practice guidelines for the screening and management of LTBI in at-risk patients have been developed. We assessed the scope, quality and consistency of clinical practice guidelines on screening for LTBI and the prevention of tuberculosis infection (TB) in high-risk patient populations.

DESIGN

We conducted a systematic review of clinical practice guidelines. Methodological quality of these guidelines was assessed using the Appraisal of Guidelines for Research and Education (AGREE) II instrument. Textual synthesis was used to summarise and compare the recommendations.

DATA SOURCES

Electronic databases (MEDLINE, EMBASE, PsycINFO) and guideline registries were searched from inception to December 2017.

RESULTS

Thirty-eight guidelines were included. Nineteen focused on patients receiving medical immunosuppression, seven on transplantation, three on patients with HIV and nine were generalised across all at risk populations. Most guidelines (n=32, 84%) used a systematic approach to identify and appraise the evidence. The methodological quality of the guidelines varied with the overall mean AGREE II scores ranging from 35% to 80%. Guidelines performed poorly in terms of editorial independence (average score 35%, range 0%-92%); however, most were robust in defining their scope and purpose (average score 80%, range 56%-100%). Guidelines recommended either or both the tuberculin skin test and the interferon gamma release assay for screening. Treatment of LTBI with isoniazid was consistently recommended.

CONCLUSION

Clinical practice guidelines on LTBI vary in quality and scope. The recommendations for screening varied across guidelines, while recommendations for treatment were largely consistent. Improving the consistency and quality of guidelines may help to optimise the screening and management of LTBI for improved patient outcomes.

Enzymatic sialylation of IgA1 O-glycans: implications for studies of IgA nephropathy

Patients with IgA nephropathy (IgAN) have elevated circulating levels of IgA1 with some O-glycans consisting of galactose (Gal)-deficient N-acetylgalactosamine (GalNAc) with or without N-acetylneuraminic acid (NeuAc). We have analyzed O-glycosylation heterogeneity of naturally asialo-IgA1 (Ale) myeloma protein that mimics Gal-deficient IgA1 (Gd-IgA1) of patients with IgAN, except that IgA1 O-glycans of IgAN patients are frequently sialylated. Specifically, serum IgA1 of healthy controls has more α2,3-sialylated O-glycans (NeuAc attached to Gal) than α2,6-sialylated O-glycans (NeuAc attached to GalNAc). As IgA1-producing cells from IgAN patients have an increased activity of α2,6-sialyltransferase (ST6GalNAc), we hypothesize that such activity may promote premature sialylation of GalNAc and, thus, production of Gd-IgA1, as sialylation of GalNAc prevents subsequent Gal attachment. Distribution of NeuAc in IgA1 O-glycans may play an important role in the pathogenesis of IgAN. To better understand biological functions of NeuAc in IgA1, we established protocols for enzymatic sialylation leading to α2,3- or α2,6-sialylation of IgA1 O-glycans. Sialylation of Gal-deficient asialo-IgA1 (Ale) myeloma protein by an ST6GalNAc enzyme generated sialylated IgA1 that mimics the Gal-deficient IgA1 glycoforms in patients with IgAN, characterized by α2,6-sialylated Gal-deficient GalNAc. In contrast, sialylation of the same myeloma protein by an α2,3-sialyltransferase yielded IgA1 typical for healthy controls, characterized by α2,3-sialylated Gal. The GalNAc-specific lectin from Helix aspersa (HAA) is used to measure levels of Gd-IgA1. We assessed HAA binding to IgA1 sialylated at Gal or GalNAc. As expected, α2,6-sialylation of IgA1 markedly decreased reactivity with HAA. Notably, α2,3-sialylation also decreased reactivity with HAA. Neuraminidase treatment recovered the original HAA reactivity in both instances. These results suggest that binding of a GalNAc-specific lectin is modulated by sialylation of GalNAc as well as Gal in the clustered IgA1 O-glycans. Thus, enzymatic sialylation offers a useful model to test the role of NeuAc in reactivities of the clustered O-glycans with lectins.

[Formation of IgA deposits in Berger's disease: what we learned from animal models]

Immunoglobulin A (IgA) nephropathy (N) is the most common form of primary glomerulonephritis in the world and one of the first cause of end-stage renal failure. IgAN is characterized by the accumulation in mesangial areas of immune complexes containing IgA1. While epidemiology and clinical studies of IgAN are well-established, the mechanism(s) underlying disease development is poorly understood. The pathogenesis of this disease involves the deposition of polymeric and undergalactosylated IgA1 in the mesangium. Quantitative and structural changes of IgA1 play a key role in the development of the disease, due to functional abnormalities of two IgA receptors: the FcαR (CD89) expressed by blood myeloid cells and the transferrin receptor (TfR1) on mesangial cells. Abnormal IgA induces release of soluble CD89, responsible for the formation of circulating IgA complexes. These complexes are trapped by the TfR1 that is overexpressed on mesangial cells in IgAN patients, inducing the expression of transglutaminase 2. This enzyme stabilises IgA deposits at the surface of mesangial cells. These cells are then activated, proliferate and produce proinflammatory cytokines, leading to the loss of renal function.

Pregnancy in renal transplant recipients: a UK national cohort study

BACKGROUND AND OBJECTIVES

Most reports of pregnancy outcome in women with kidney transplants are single-center, retrospective, and include small numbers and few are compared with controls. The aim of this study was to collect information about pregnancy outcomes among all kidney transplant recipients in the United Kingdom, managed with current antenatal and nephrologic care, and to compare these data with a contemporaneous control group.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Pregnant women with a kidney transplant were identified through the UK Obstetric Surveillance System (UKOSS) between January 1, 2007 and December 31, 2009. Data on a comparison cohort were obtained from the UKOSS database, containing information on comparison women identified in previous studies. Outcomes were also compared with national data.

RESULTS

There were 105 pregnancies identified in 101 recipients. Median prepregnancy creatinine was 118 μmol/L. Preeclampsia developed in 24% compared with 4% of the comparison group. Median gestation at delivery was 36 weeks, with 52% of women delivering at <37 weeks, significantly higher than the national rate of 8%. Twenty-four infants (24%) were small for gestational age (<10th centile). There were two (2%) cases of acute rejection. Potential predictive factors for poor pregnancy outcome included >1 previous kidney transplant (P=0.03), first trimester serum creatinine >125 μmol/L (P=0.001), and diastolic BP >90 mmHg in the second (P=0.002) and third trimesters (P=0.05).

CONCLUSIONS

Most pregnancies in the United Kingdom in women with kidney transplants are successful but rates of maternal and neonatal complications remain high.

Establishment of a mouse IgA nephropathy model with the MBP-20-peptide fusion protein

Here, we aimed to determine whether immunoglobulin-A nephropathy (IgAN) could be induced in Balb/c mice by immunizing them with a fusion protein (MBP-20 peptide) comprising the maltose-binding protein (MBP) and a 20-amino-acid peptide derived from Staphylococcus aureus. A recombinant plasmid encoding the fusion protein was constructed and expressed in bacterial cells. The synthetic 20-peptide was used to prepare the monoclonal antibody. Balb/c mice were immunized with the MBP-20-peptide fusion protein over a 21-week course before renal histology was examined at the light and electron microscopic levels. Direct immunofluorescence staining with the anti-20-peptide monoclonal antibody was also performed using renal biopsy tissue from human IgAN patients as a comparison. IgA and IgG specific for the 20-peptide in human and mice serum were detected. The IgAN experimental mice developed a clinical and pathological profile that closely resembled that of human IgAN patients, including the induction of hematuria and numerous histopathological features. Levels of IgA and IgG specific for the 20-peptide were significantly increased in serum from the IgAN experimental mice and IgAN patients compared with control mice and non-IgAN patients. In IgAN model mice, the anti-20-peptide antibody labeled glomeruli, while the antibody strongly labeled glomeruli and weakly labeled tubular epithelial cells in renal tissue from human IgAN patients. In conclusion, immunization with an MBP-20-peptide fusion protein is able to induce clinical and pathological features closely resembling IgAN in Balb/c mice, indicating a potentially useful role for the model in the study of IgAN and related diseases.

Cyclosporine A exposure during pregnancy in mice: effects on reproductive performance in mothers and offspring

BACKGROUND

Pregnancies after organ transplantation and under immunosuppressive treatment are associated with slightly elevated risks for obstetric and post-natal complications but can usually be managed well. However, little is known about the effects of intrauterine exposure (IUE) to immunosuppressants in the growing and adult offspring. One major issue is the potentially negative effects of immunosuppressive medication on reproduction. This study investigates the effect of exposure during pregnancy to the most commonly used immunosuppressant in organ transplantation, cyclosporine A (CsA), on the reproductive outcome in mothers and offspring.

METHODS

Female C57CBA-F1 mice received 0, 10, 20 or 30 mg/kg bodyweight of CsA daily by subcutaneous mini-osmotic pumps during mating and pregnancy. Blood concentrations of CsA, implantation rates, resorption rates and fetal weights were analysed. In addition, female and male mice exposed to CsA in utero were mated to unexposed partners and pregnancy outcomes were analysed.

RESULTS

Direct maternal exposure to CsA at high doses reduced implantation rates and fetal survival. IUE to CsA reduced adolescent growth but did not affect fertility, although a reduction in birthweight was seen in offspring of females exposed to CsA in utero.

CONCLUSIONS

CsA exposure during pregnancy correlates with impaired reproductive outcome, but offspring fertility is not affected. The cause of reduction in adolescent weight gain and low birthweight in offspring of females exposed to CsA in utero need further investigation.

O-linked oligosaccharides of the IgA1 hinge region: roles of its aberrant structure in the occurrence and/or progression of IgA nephropathy

Primary IgA nephropathy (IgAN) has been regarded as an immune complex-mediated glomerulonephritis characterized immunohistologically by the predominant deposition of IgA in the glomerular mesangial area with a variety of histopathologic injuries (Clarkson et al. in Ann Rev Med 38:157-168, 1987). In 1992, the characteristic structure of O-linked oligosaccharides (O-glycans) in the IgA1 hinge and its possible aberrancy were simultaneously and independently proposed by Mesteckey et al. (Cont Nephrol 104:172-182, 1993), and our group (Cont Nephrol 104:217, 1993) at the International Congress of Nephrology (IgA Nephropathy 25th year) held in Nancy, France. Since then, the aberrancy has been confirmed by several research groups and is suspected to play a role in the occurrence and/or the progression of IgAN. At the end of the 1980s, I took an interest in the existence of O-glycans in the hinge region of IgA1 and have pursued the structure of the carbohydrate chains. Since an excellent review on the structure and the role of the carbohydrate in IgA molecules was recently published by Narita et al. (Clin Ex Nephrol 12:332-338, 2008), this review focuses on the process by which I developed the idea of aberrant O-glycosylation in IgA1 molecules in IgAN patients and summarizes our recent observations concerning IgA1 molecules.

T cell cytokine polarity as a determinant of immunoglobulin A (IgA) glycosylation and the severity of experimental IgA nephropathy

Immunoglobulin A (IgA) glycosylation, recognized as an important pathogenic factor in IgA nephropathy (IgAN), is apparently controlled by the polarity of T helper (Th) cytokine responses. To examine the role of cytokine polarity in IgAN, inbred mice were immunized by intraperitoneal priming with inactivated Sendai virus (SeV) emulsified in either complete Freund's adjuvant (CFA) or incomplete Freund's adjuvant (IFA), which promote Th1- or Th2-immune response, respectively, and then boosted identically twice orally with aqueous suspensions of inactivated virus. Next, some mice were challenged intranasally with infectious SeV. Mice primed with CFA or IFA had equal reductions in nasal viral titre relative to non-immune controls, and equally increased serum levels of SeV-specific IgA antibody. Mice primed with CFA showed higher SeV-specific IgG than those with IFA. Splenocytes from mice primed with IFA produced copious amounts of interleukin (IL)-4 and IL-5, but little interferon-gamma and IL-2; those primed with CFA had reciprocal cytokine recall responses. Total serum IgA and especially SeV-specific IgA from mice primed with IFA showed a selective defect in sialylation and galactosylation. Although the frequency and intensity of glomerular deposits and haematuria did not differ, glomerulonephritis in mice primed with IFA and challenged with infectious virus was more severe than in those given CFA, as judged by serum creatinine level. We conclude that the polarity of T cell cytokines controls the pattern of IgA glycosylation and exerts direct or indirect effects on functional glomerular responses to immune complex deposition.

IgA1 desialylated by microbial neuraminidase forms immune complex with naturally occurring anti-T antibody in human serum

IgA1 was identified as the most prominent O-glycosylated protein of human serum. Desialylation by bacterial (Clostridium perfringens) neuraminidase rendered dot-blotted IgA1 recognizable by the naturally occurring serum antibody (anti-T) directed against Thomsen-Friedenreich antigen, Galbeta1-->3GalNAc-alpha-. On Western blot of serum O-glycosylated proteins anti-T recognized nearly all the bands including IgA1 as did the T antigen-specific animal lectin galectin-1 but only after their desialylation. Agglutination of desialylated human erythrocytes by anti-T was effectively inhibited by desialylated IgA1, but not by native IgA1 or other immunoglobulins. Desialylation of serum by neuraminidase led to significantly increased formation of immune complexes containing IgM, the major immunoglobulin type in anti-T on one hand and O-glycosylated proteins/IgA1 on the other. In further evidence for anti-T-desialylated IgA1 immune complex formation, purified anti-T added to desialylated, but not native serum led to formation of additional IgA-IgM immune complexes. Also neuraminidase treatment significantly reduced the titre of free (non-immune complexed) anti-T in serum, while selective removal of anti-T by affinity absorption resulted in considerable decrease in the amount of IgA1 that got converted to immune complexes following enzymatic desialylation of serum. Formation of immune complex between anti-T and neuraminidase-treated IgA1 in serum may be significant since many disease pathogens release neuraminidase and since IgA1 is a powerful ligand for tissue galectin-1 more so after desialylation. Diabetes also raises serum IgA and neuraminidase levels.

The pathogenic role of IgA1 O-linked glycosylation in the pathogenesis of IgA nephropathy

Numerous abnormalities of the IgA immune system have been reported in IgAN but the most consistent finding remains aberrant IgA1 O-linked glycosylation of the IgA1 hinge region. The defect comprises reduced galactosylation of O-linked N-acetylgalactosamine residues with or without changes in the terminal sialylation of the O-linked sugars. Aberrant O-galactosylation has been found in serum IgA1, in IgA1 isolated from tonsillar lymphocytes, and in IgA1 eluted from mesangial deposits. There is evidence that changes in IgA1 O-galactosylation lead to IgA immune complex formation and mesangial IgA deposition. Mesangial cells exposed to these IgA immune complexes proliferate and adopt a pro-inflammatory phenotype; they secrete cytokines, chemokines, growth factors and extracellular matrix components promoting glomerular inflammation and glomerulosclerosis. Recent evidence suggests that the control of IgA1 O-glycosylation is linked to class switching from IgD to IgA1 synthesis and that the pattern of IgA1 O-glycosylation may be programmed at the time of initial antigen encounter. IgA1 glycosylation varies between systemic and mucosal sites and the association of aberrant IgA1 galactosylation with low affinity, polymeric IgA1 antibodies against mucosal antigens suggests undergalactosylated IgA1 may in fact be a mucosal glycoform of IgA1. Although suited to the mucosal compartment, when these IgA1 glycoforms enter the systemic circulation in appreciable quantities they deposit in the mesangium and trigger glomerular inflammation. This review will discuss the evidence for the role of IgA1 O-glycosylation in the pathogenesis of IgAN and propose an explanation for the presence of aberrantly O-glycosylated IgA1 in the circulation of patients with IgAN.

Protective role of anti-synthetic hinge peptide antibody for glomerular deposition of hypoglycosylated IgA1

BACKGROUND

The KM mouse lacks endogenous genes for immunoglobulins and carries the entire human IgH locus and the IgLk transgene. Therefore, human IgA1 does not provoke a hetero-immune response. We had observed mesangial IgA deposits in KM mice given desialo-degalacto (DeS/DeGal) IgA1.

METHODS

In this study, the mice were immunized with synthetic IgA1 hinge (glyco-)peptide before administration of DeS/DeGal IgA1, and the effects of the pre-immunization were evaluated. Mice were divided into sHP, 5GalNAc-sHP and non-immunization groups. In two pre-immunization groups, KLH-conjugated sHP or KLH-5GalNAc-sHP, which has five GalNAc residues, was subcutaneously given three times every 2 weeks. Two weeks after the final pre-immunization, DeS/DeGal IgA1 was administered daily for 5 weeks. Serial serum levels of anti-sHP and anti-IgA1 antibodies were evaluated by ELISA. On the day of the last administration of IgA1, renal biopsy was performed.

RESULTS

Mesangial IgA deposits were observed in all non-immunized mice. In pre-immunized mice, IgA deposition was not detected in 6 of 13 sHP mice and 1 of 4 5GalNAc-sHP mice. The intensities of IgA deposits were significantly different between sHP groups and non-immunized (P = 0.003) groups. There was a significant inverse correlation between the intensities of IgA deposits and the anti-sHP antibody titers (P = 0.016).

CONCLUSIONS

These results suggest that the anti-IgA1 hinge peptide antibody plays a role in the inhibition of glomerular IgA deposition.

Idiopathic IgA Nephropathy: Pathogenesis, Histopathology, and Therapeutic Options

IgA nephropathy is one of the most common causes of glomerulonephritis in the world. Proliferative and crescentic forms of IgA are found in up to 30% of cases and are associated with nephrotic-range proteinuria, accelerated hypertension, and accelerated decline toward ESRD. Despite its prevalence and clinical importance, there is no unifying nomenclature or consensus for the treatment of specific histologic subgroups. As a consequence, the development of clinically effective treatment regimens for IgA nephropathy have lagged behind other, less common forms of glomerulonephritis. Herein is reviewed the pathogenesis and histologic subtypes of IgA nephropathy and how conventional and immunosuppressive therapies have an impact on renal survival and recurrence rates. The use of known clinical risk factors for disease progression in conjunction with specific histologic features can be a guide to both induction and consolidation therapies for individual patients with IgA nephropathy.

Differential binding characteristics of native monomeric and polymeric immunoglobulin A1 (IgA1) on human mesangial cells and the influence of in vitro deglycosylation of IgA1 molecules

Recent studies had demonstrated that serum and mesangial immunoglobulin A1 (IgA1) in patients with IgA nephropathy (IgAN) were polymeric and deglycosylated. The current study was to investigate the binding characteristics of monomeric and polymeric normal human IgA1 on mesangial cells and the influence of in vitro deglycosylation of IgA1 molecules. The normal human IgA1 was desialylated and degalactosylated with specific enzymes, respectively. The monomeric IgA1 (mIgA1) and polymeric IgA1 (pIgA1) were separated by Sephacryl S-300 chromatography. The binding capacities of the mIgA1 and pIgA1 to primary human mesangial cells (HMC) were evaluated by classical radioligand assay. Both the native mIgA1 and pIgA1 could bind to HMC in a dose-dependent and saturable manner. The maximal binding capacity of the native pIgA1 were significantly higher than that of the native mIgA1 (P < 0.05). However, the affinity of the native mIgA1 was almost 100 times higher than that of the native pIgA1. After deglycosylation, binding of the two deglycosylated mIgA1 to HMC could not be detected. However, the maximal binding capacities of the two deglycosylated pIgA1 to HMC were increased significantly compared with that of native pIgA1. The affinity of the two deglycosylated pIgA1 was similar to that of native pIgA1 (P > 0.05). The current study suggests differential binding characteristics of native monomeric and polymeric IgA1 on mesangial cells. Glycosylation of IgA1 molecules could significantly affect the binding of IgA1 on HMC.

Development of immunoglobulin A nephropathy- like disease in beta-1,4-galactosyltransferase-I-deficient mice

Beta4 galactosylation of glycoproteins plays important roles in protein conformation, stability, transport, and clearance from the circulation. Recent studies have revealed that aberrant glycosylation causes various human diseases. Here we report that mice lacking beta-1,4-galactosyltransferase (beta4GalT)-I, which transfers galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a beta-1,4 linkage, spontaneously developed human immunoglobulin A nephropathy (IgAN)-like glomerular lesions with IgA deposition and expanded mesangial matrix. beta4GalT-I-deficient mice also showed high serum IgA levels with increased polymeric forms as in human IgAN. IgAN is the most common form of glomerulonephritis, and a significant proportion of patients progress to renal failure. However, pathological molecular mechanisms of IgAN are poorly understood. In humans, abnormal character of serum IgA, especially serum IgA1 with aberrant galactosylation and sialylation of O-glycans in its hinge region is thought to contribute to the pathogenesis of IgAN. Mouse IgA has N-glycans but not O-glycans, and beta4-galactosylation and sialylation of the N-glycans on the serum IgA from beta4GalT-I-deficient mice was completely absent. This is the first report demonstrating that genetic remodeling of protein glycosylation causes IgAN. We propose that carbohydrates of serum IgA are involved in the development of IgAN, whether the carbohydrates are O-glycans or N-glycans.

IgA and IgA-specific receptors in human disease: structural and functional insights into pathogenesis and therapeutic potential

IgA antibodies play an important role in humoral immunity. IgA is the predominant antibody in mucosal secretions and the second most prevalent in the serum. It occupies a unique position among human antibodies in that it can both trigger and suppress inflammatory responses, depending on the situation. Recent structural and functional studies have revealed details of the structure of IgA and its interaction with key cell-surface receptors. We look at the role IgA and IgA receptors (particularly FcalphaRI) play in the pathogenesis of diseases such as IgA nephropathy and other autoimmune conditions. Finally, we address the potential of IgA as a therapeutic tool to either trigger specific inflammatory responses to destroy target cells or suppress inflammatory responses in the case of autoimmune diseases, and the promise of mucosal vaccines for eliciting specific IgA responses to pathogens in mucosal environments.

Self-aggregated deglycosylated IgA1 with or without IgG were associated with the development of IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, with various pathological phenotypes. Our previous study suggested that aberrant glycosylation of serum IgA1 was associated with different pathological phenotypes of IgAN, and substantial evidence indicated that deglycosylated IgA1 had an increased tendency to form macromolecules. The aim of the current study was to investigate the composition of IgA1-containing macromolecules in different pathological phenotypes of IgAN. Sera from 10 patients with mild mesangial proliferative IgAN (mIgAN), 10 with focal proliferative sclerosing IgAN (psIgAN) and 10 healthy blood donors were collected. The sera were applied and IgA1 binding proteins (IgA1-BP) were eluted from the columns immobilized with desialylated IgA1 (DesIgA1/Sepharose) or desialylated/degalactosylated IgA1 (DesDeGalIgA1/Sepharose), respectively. The amounts of IgA1 and IgG and the glycoform of IgA1 in the IgA1-BP were detected by enzyme-linked immunosorbent assays (ELISAs) and were compared between patients with different pathological phenotypes and normal controls. The amount of IgA1 in IgA1-BP eluted from both columns was significantly higher in patients with both pathological phenotypes of IgAN than in normal controls. In IgA1-BP eluted from DesDeGalIgA1/Sepharose, the desialylation of IgA1 was much more pronounced in patients with both pathological phenotypes of IgAN than in normal controls, while the degalactosylation of IgA1 was much more pronounced only in patients with psIgAN than in normal controls. Furthermore, the amount of IgG in IgA1-BP eluted from DesDeGalIgA1/Sepharose was significantly higher in patients with psIgAN than in normal controls. In patients with psIgAN, the amount of IgG eluted from DesDeGalIgA1/Sepharose was much greater than from DesIgA1/Sepharose. In conclusion, self-aggregated deglycosylated IgA1 with or without IgG were associated with the development of IgAN.

Binding capacity of in vitro deglycosylated IgA1 to human mesangial cells

IgA nephropathy (IgAN) is the most common glomerular disease and it is characterized by deposition of IgA1 molecules in mesangium. Recent studies had demonstrated that serum and mesangial IgA1 in IgAN were deglycosylated and IgA1 could bind to human mesangial cells (HMC) through a novel receptor. The aim of the current study is to investigate and compare the binding capacities of different in vitro deglycosylated IgA1 on human mesangial cells. Serum IgA1 was purified by jacalin affinity chromatography and then was desialylated (DesIgA1) and/or degalactosylated (Des/DeGalIgA1) with neuraminidase and/or beta-galactosidase. The efficacy of deglycosylations was assessed by Peanut agglutinin (PNA) and Vicia villosa (VV) lectin. The sizes of normal IgA1 and deglycosylated IgA1 were determined by Sephacryl S-300 chromatography and binding capacities to primary HMC were evaluated by radioligand binding assays. Normal IgA1 and deglycosylated IgA1 could bind to HMC in a dose-dependent, saturable manner. The maximal binding capacities and binding sites/cell of DesIgA1 and Des/DeGalIgA were significantly higher than that of normal IgA1. However, more aggregated IgA1 was found in DesIgA1 and Des/DeGalIgA1. Scatchard analysis revealed a similar Kd of normal IgA1 and deglycosylated IgA1. The current study suggested that the binding capacities of DesIgA1 and Des/DeGalIgA1 to HMC were significantly higher than that of normal IgA1, which at least in part was due to more macromolecular IgA1 in deglycoslated IgA1. However, there were no significant differences in the affinities of normal IgA1, DesIgA1 and Des/DeGalIgA1 with HMC. Deglycosylated IgA1 might play an important role in pathogenesis of IgAN.

The glycans deficiencies of macromolecular IgA1 is a contributory factor of variable pathological phenotypes of IgA nephropathy

Recent evidence has suggested that IgA1-containing macromolecules and the glycosylation of IgA1 in sera from patients with IgAN might involve the pathogenesis of IgAN. However, whether the different histological phenotypes can be attributed or not to the aberrant glycosylation of macromolecular IgA1 has not yet been elucidated. The aim of the current study is to investigate the glycosylation of IgA1 molecules in serum IgA1-containing macromolecules and their association with pathological phenotypes of IgAN. Sera was collected from 40 patients with IgAN and 20 donors. Twenty patients had mild mesangial proliferative IgAN, the remaining 20 had focal proliferative sclerosing IgAN. Polyethylene glycol 6000 was used to precipitate the macromolecules from sera of patients and controls. Biotinylated lectins were used in an enzyme-linked immunosorbent assay (ELISA) to examine different glycans on IgA1 molecules. The alpha2,6 sialic acid was detected by elderberry bark lectin (SNA) and the exposure of terminal galactose (Gal) and N-acetylgalactosamine (GalNAc) were detected by Arachis hypogaea (PNA) and Vilsa villosa lectin (VVL), respectively. The IgA1 glycans levels corrected by IgA1 concentrations were compared between patients and controls. Reduced terminal alpha2,6 sialic acid of IgA1 (79.89 +/- 25.17 versus 62.12 +/- 24.50, P = 0.034) was demonstrated only in precipitates from sera of patients with focal proliferative sclerosing IgAN, compared with those from controls. Reduced galactosylation of IgA1 molecules in precipitates was demonstrated in patients with both mild mesangial proliferative IgAN and focal proliferative sclerosing IgAN compared with normal controls (24.52 +/- 18.71 versus 76.84 +/- 32.59 P = 0.000 and 33.48 +/- 25.36 versus 76.84 +/- 32.59 P = 0.000). However, no significant difference was found in IgA1 glycosylation in the supernatant between patients and normal controls (P > 0.05). The glycosylation deficiency of IgA1 existed only in serum IgA1-containing macromolecules of patients with IgAN, and was associated with the renal pathological phenotypes. This suggests that aberrant glycosylation of IgA1 in serum macromolecules might be a contributory factor in the pathogenesis of IgAN.

Chromosomal mapping of hyperserum IgA and glomerular IgA deposition in a high IgA (HIGA) strain of DdY mice

BACKGROUND

The high IgA (HIGA) strain of ddY mice is an inbred model of IgA nephropathy (IgAN), established by selective mating of outbred ddY mice. HIGA mice show high levels of serum IgA and glomerulonephritis with mesangial IgA deposition. To identify the genetic loci responsible for hyperserum IgA and glomerular IgA deposition in this strain, quantitative trait loci analysis was carried out.

METHODS

By crossing HIGA with BALB/c mice, 244 F2 generations were produced. Serum IgA levels and glomerular IgA deposition were examined at 40 weeks of age. Genetic markers were typed at 105 microsatellites and the quantitative trait loci of hyperserum IgA and glomerular IgA deposition were confirmed using Map Manager QTX software.

RESULTS

Two significant quantitative trait loci of hyperserum IgA were identified on chromosome 2 [logarithm of odds (LOD) = 5.01] and chromsome 4 (LOD = 4.45), and a suggestive quantitative trait locus of hyperserum IgA was located on chromosome 1 (LOD = 3.49). On chromosome 15, a significant quantitative trait locus of glomerular IgA deposition was identified (LOD = 4.40) without the hyperserum IgA locus. Serum IgA level was weakly correlated with the intensity of glomerular IgA in 244 F2 mice; however, the quantitative trait loci of hyperserum IgA were not significantly associated with glomerular IgA deposition.

CONCLUSION

These findings indicate that, in HIGA mice, glomerular IgA deposition is mainly regulated by a quantitative trait locus on chromosome 15, and hyperserum IgA synergistically but weakly affect glomerular IgA deposition. The immune disturbance similar to IgAN was revealed to be under multigenic control in HIGA mice.

IgA: an immune glycoprotein

IgA is a glycoprotein containing multiple N-linked carbohydrates as well as O-linked glycans in the case of IgA1. Because of the critical role it plays in providing protection at mucosal surfaces, IgA is an ideal candidate for use as a therapeutic or prophylactic agent. The presence or absence of carbohydrates, as well as their structure, has been found to influence effector functions and binding to specific IgA receptors. In addition, changes in IgA glycosylation are associated with immune pathology. A thorough understanding of the contributions of the glycans to IgA immune protection will aid in the design of clinically suitable antibodies.

Aberrantly glycosylated serum IgA1 are closely associated with pathologic phenotypes of IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common glomerulonephritis with various histologic and clinical phenotypes. The mechanisms underlying the pathogenesis of IgAN remained unclear. But now altered O-glycosylation of serum IgA1 observed in these patients was considered to be a key contributory factor. The aim of the current study is to investigate whether aberrantly glycosylated IgA1 was associated with pathologic phenotypes of IgAN.

METHODS

Sera from 107 patients with IgAN recently diagnosed were collected. Fifty patients were with mild mesangial proliferative IgAN, the others were with focal proliferative and sclerosing IgAN. Sera from 22 normal blood donors were used as normal controls. Biotinylated lectins were used in enzyme-linked immunosorbent assay (ELISA) to examine different glycans on IgA1 molecules. The alpha2,6 sialic acid was detected by elderberry bark lectin (SNA), the exposure of terminal galactose (Gal) and N-acetylgalactosamine (GalNAc) were detected by arachis hypogaea [peanut agglutinin (PNA)] and vilsa villosa lectin (VVL), respectively. The serum IgA1 glycans levels corrected by serum IgA1 concentrations were compared between patients and controls.

RESULTS

Reduced terminal alpha2,6 sialic acid (1.16 +/- 0.21 vs. 0.98 +/- 0.31) (P= 0.008) and galactosylation (0.30 +/- 0.29 vs. 0.16 +/- 0.19) (P= 0.029) increased exposure of (GalNAc) (0.00 vs. 0.03) (P= 0.024) were demonstrated in serum IgA1 from patients with IgAN as compared with those in controls. More important, the exposures of 2,6 sialic acid and Gal were significantly decreased, especially in patients with focal proliferative and sclerosing IgAN compared with that in patients with mild mesangial proliferative IgAN (0.91 +/- 0.34 vs. 1.05 +/- 0.25) (P= 0.014) (0.108 +/- 0.137 vs. 0.221 +/- 0.219) (P= 0.018). However, no significant difference was found between patients with mild mesangial proliferative IgAN and normal controls (P > 0.05). The exposure of GalNAc of serum IgA1 from patients with focal proliferative and sclerosing IgAN was significantly higher than that of controls (P= 0.017), but had no statistical difference with that of patients with mild mesangial proliferative IgAN.

CONCLUSION

The desialylation and degalactosylation of IgA1 in sera of patients with IgAN were closely associated with pathologic phenotypes.

IgA nephropathy and tonsils--an approach from the structure of IgA1 produced by tonsillar lymphocytes

Human immunoglobulin A1 (IgA1), which is the predominant subtype to be deposited in glomeruli in IgA nephropathy (IgAN), has a unique mucine-like structure in its hinge region. Namely, it contains O-glycans and proline-rich peptides We previously observed underglycosylation of the hinge region in serum and deposited IgA1 in IgAN. On the other hand, clinical development and exacerbation of IgAN are frequently preceded by episodes of upper respiratory tract infection, and palatine tonsils represent the predominant immunocompetent tissue of the upper respiratory tract. Therefore, we hypothesized that tonsils were one of the origins of glomerular IgA1 in IgAN, and investigated the O-glycan structure of IgA1 produced by tonsillar lymphocytes (tonsillar IgA1). A significant increase in asialo-agalacto type O-glycans was found in the tonsillar IgA1 hinge in IgAN. These results suggest that the tonsils produce underglycosylated IgA1 molecules, which enter the bloodstream and are then deposited in the glomeruli.

Detection of gender difference and epitope specificity of IgG antibody activity against IgA1 hinge portion in IgA nephropathy patients by using synthetic hinge peptide and glycopeptide probes

BACKGROUND AND AIMS

There are many reports on the presence of an incompletely glycosylated O-linked oligosaccharide(s) on the IgA1 hinge region in some immunoglobulin (IgA) nephropathy patients. Furthermore, the production of an antibody against the naked hinge peptide portion was reported in an IgA nephropathy patient. In this report, characterization of the IgG antibody against the hinge portion was carried out by using synthetic hinge glycopeptide probes.

METHODS AND RESULTS

The following synthetic hinge peptide and glycopeptides were prepared: 19mer peptide, V-P-S-T-P-P-T-P-S-P-S-T-P-P-T-P-S-P-S (designated HP), the peptide having a single alpha-linked GalNAc residue at positions 4, 7, 9, 11 and 15 (4 GN - 15 GN, respectively) and the same peptide having five GalNAc residues at all five positions (GN5). The mean value of the antibody activity against these probes was compared with each other. The highest activity against the naked hinge peptide (HP) and lowest activity against the fully glycosylated hinge peptide (GN5) were obvious. As attachment of GalNAc to position 4 or 11 on the peptide brought about a significant reduction of the activity against the naked hinge peptide, the P-S-T-P sequence included in both positions was thought to be the most probable site recognized by these antibodies. As an additional unexpected observation, a gender difference in this antibody activity against all the probes was found. The antibody activity in a female was significantly higher compared with that in a male.

CONCLUSION

Because the frequency of incidence of IgA nephropathy is known to be slightly higher in males, this gender difference might indicate a protective meaning to remove aberrantly glycosylated molecules from the patient's serum.

Aberrant glycosylation in IgA nephropathy (IgAN)

Immunoglobulin A nephropathy (IgAN) patients exhibit circulating IgA1 with reduced galactose (Gal) and/or sialic acid (Neu5Ac) and increased exposure of N-acetylgalactosamine (GalNAc). These IgA glycoforms fix complement and in mesangial cells regulate integrin expression, enhance nitric oxide synthase (NOS) activity, decrease endothelial growth factor synthesis, meanwhile depressing proliferation and increasing apoptosis. Drugs can be targeted to the effects enhanced by aberrantly glycosylated IgA1 on mesangial cells. Recent data suggest that aberrant IgA1 glycosylation may modulate clinical expression and progression of IgAN.

Pathogénie de la maladie de Berger : implication des immunoglobulines A et de leurs récepteurs

Immunoglobulin A (IgA) nephropathy or Berger's disease is the most common form of primary glomerulonephritis in the world and one of the first cause of end-stage renal failure. IgA nephropathy is characterized by the accumulation in mesangial areas of immune complexes containing polymeric IgA1. While epidemiology and clinical studies of IgA nephropathy are well established, the mechanism(s) underlying disease development is poorly understood. The pathogenesis of this disease involves the deposition of polymeric and undergalactosylated IgA1 in the mesangium. Quantitative and structural changes of IgA1 play a key role in the development of the disease due to functional abnormalities of two IgA receptors: The FcalphaR (CD89) expressed by blood myeloid cells and the transferrin receptor (CD71) on mesangial cells. Abnormal IgA induce the release of soluble CD89 which is responsible for the formation of circulating IgA complexes. These complexes may be trapped by CD71 that is overexpressed on mesangial cells in IgA nephropathy patients allowing pathogenic IgA complex formation.

IgA1 molecules produced by tonsillar lymphocytes are under-O-glycosylated in IgA nephropathy

BACKGROUND

Human serum immunoglobulin A1 (IgA1) has a unique mucine-like structure in its hinge region that contains O-glycans and proline-rich peptides. We previously reported the under-O-glycosylation of the hinge in serum IgA1 and deposited IgA1 in glomeruli (glomerular IgA1) in IgA nephropathy. The clinical development and exacerbation of IgA nephropathy frequently are preceded by episodes of upper respiratory tract infections. Therefore, tonsils, which represent the predominant immunocompetent tissue of the upper respiratory tract, may be related to the pathogenesis of IgA nephropathy. In this study, we investigated the O-glycan structure of IgA1 produced by tonsillar lymphocytes (tonsillar IgA1), suspecting that tonsillar IgA1 is one of the origins of glomerular IgA1 in patients with IgA nephropathy.

METHODS

Extracted tonsils were obtained from 7 patients with IgA nephropathy and 5 patients with chronic tonsillitis as controls. Tonsillar lymphocytes separated from extracted tonsils were cultured for 7 days, and IgA1 in the culture medium was purified. The varieties of O-glycans in tonsillar IgA1 were determined from the molecular weights measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RESULTS

A significant increase in the percentage of asialo-agalacto type O-glycans was found in tonsillar IgA1 in 4 of 7 patients with IgA nephropathy (57.1%) compared with controls. Between the IgA nephropathy and control groups, the difference was statistically significant (P = 0.047).

CONCLUSION

This study provides precise information about the structure of O-glycans in tonsillar IgA1 in patients with IgA nephropathy. Our results suggest that tonsils produced the underglycosylated IgA1 molecules in patients with IgA nephropathy.