Underglycosylation of IgA1 hinge plays a certain role for its glomerular deposition in IgA nephropathy

This study was performed to isolate and investigate the IgA1 that could accumulate in glomeruli (glomerulophilic IgA1). IgA1 was fractionated by the electric charge and the reactivity to Jacalin. Serum IgA1 of IgA nephropathy patients was separated and fractionated using a Jacalin column and subsequent ion-exchange chromatography. The fractions were divided into three groups of relatively cationic (C), neutral (N), and anionic (A). IgA1 was also divided into Jacalin low (L), intermediate (I), and high (H) affinity fractions by serial elution using 25, 100, and 800 mM galactose. The left kidneys of Wistar rats were perfused with 2, 5, or 10 mg of each group of IgA1. The rats were sacrificed 15 min, 30 min, 3 h, or 24 h after the perfusion. The accumulation of each IgA1 in the glomeruli was then observed by immunofluorescence. The IgA1 of the fractions N and H separated by the two methods was definitely accumulated in the rat glomeruli with a similar pattern. The electrophoresis revealed that the macromolecular IgA1 was increased in fraction H compared with other fractions. Therefore, Jacalin high-affinity IgA1(fraction H) was applied on a diethylaminoethyl column and divided into electrically cationic (HC), neutral (HN), and anionic (HA). Only the asialo-Galbeta1,3GalNAc chain was identified in the fraction HN IgA1 by gas-phase hydrazinolysis. Furthermore, the IgA1 fraction was strongly recognized by peanut agglutinin, Vicia Villosa lectins, and antisynthetic hinge peptide antibody. These results indicated that the IgA1 molecules having the underglycosylated hinge glycopeptide played a certain role in the glomerular accumulation of IgA1 in IgA nephropathy.     

Tonsillar IgA1 as a possible source of hypoglycosylated IgA1 in the serum of IgA nephropathy patients.

BACKGROUND: There are many reports of incompletely glycosylated O-linked oligosaccharides on the IgA1 hinge region in certain IgA nephropathy patients. In addition, other reports have noted a relationship between tonsillectomy and IgA nephropathy. METHODS: Immunoglobulins from extracts of tonsillectomized tissue and other sources were analysed by isoelectric focusing (IEF) and by enzyme-linked immunosorbent assay (ELISA). RESULTS: The IEF profile of tonsillar IgA differed from that of serum IgA and it was enriched in cationic IgA. However, extracts from tonsillitis controls and IgA nephropathy patients exhibited profiles that were very similar. Enzymatic removal of sialic acid induced a shift of the peaks to the cathode side. The profiles of IgA from treated tonsillar extract and treated serum were closely overlapped. In addition, asialo Galbeta1,3GalNAc was clearly present in cationic IgA from tonsillar extract and in aberrant IgA1 from serum following enzymatic transfer of sialic acid to IgA1. Serum IgA also contained partly sialylated IgA1. Quantitative analysis of IgA and IgG in the extracts indicated that IgA was significantly higher, whereas IgG was significantly lower in IgA nephropathy patients. CONCLUSIONS: We found that the IgA1 produced in tonsillar tissue differed from serum IgA1. Furthermore, an overproduction of asialo IgA1 resulted from the disordered balance between IgA- and IgG-producing cells in the tonsils from the IgA nephropathy patient. Although it is unclear how such asialo IgA1 molecules are transferred from tonsil tissue to serum, a tonsillar source may produce a few micrograms of aberrant IgA1 that then appears in serum.     

Injection of recombinant FcalphaRI/CD89 in mice does not induce mesangial IgA deposition.

BACKGROUND: Earlier studies have suggested that complexes of the human IgA receptor FcalphaRI/CD89 with mouse IgA are pathogenic upon deposition in the renal mesangium. Transgenic mice expressing FcalphaRI/CD89 on macrophages/monocytes developed massive mesangial IgA deposition and a clinical picture of IgA nephropathy (IgAN). Based on these findings, the purpose of this study was to design an experimental model of IgAN by injection of human CD89 in mice. The interaction of mouse IgA with CD89 was investigated further. METHODS: Recombinant human soluble CD89 and a chimeric CD89-Fc protein were generated, produced, purified and injected in mice. Renal cryosections were stained for IgA and CD89. The interaction of mouse IgA with CD89 was analysed by fluorescence-activated cell sorting (FACS) analysis, enzyme-linked immunosorbent assay (ELISA) and plasmon resonance technology. RESULTS: Injection of recombinant human CD89 did not result in significant IgA or CD89 deposition in the renal mesangium. However, CD89 staining in the liver was found to be positive. CD89 was rapidly cleared from circulation without signs of complex formation with IgA. FACS analysis, ELISA and plasmon resonance techniques all revealed a dose-dependent binding of human IgA to recombinant CD89, while no detectable binding was seen of mouse IgA, either of serum IgA or of different monoclonal mouse IgA preparations. CONCLUSIONS: An experimental model for IgAN in mice could not be obtained by injection of recombinant CD89. This is compatible with our in vitro biochemical data showing a lack of binding between recombinant human CD89 and mouse IgA.     

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.     

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 α‐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.     

Pathogenic role of the IgA molecule in IgA nephropathy

SUMMARY: Deposits of IgA together with complement in different body tissues support the hypothesis that IgA can trigger inflammatory mechanisms. IgA nephropathy (IgAN) is characterized by predominant mesangial IgA₁ deposits of a polymeric nature. So far, the mechanism of polymeric IgA₁ deposition in the kidney mesangium is poorly understood in IgAN. the exact pathophysiological sequel preceding renal fibrosis following the mesangial deposition of IgA immune complexes remains speculative. Recent in vitro studies revealed that binding of IgA to mesangial cells led to increased expression of growth factors, cytokines, and integrins. the release of these proinflammatory factors is likely to enhance inflammatory injury. In addition, the local renin-angiotensin system present in renal tissues also contributes to renal fibrosis through the activation of transforming growth factor-β. the question of whether polymeric IgA isolated from patients with IgAN exerted any upregulatory effect on the synthesis of macrophage migration inhibitory factor (MIF) and components of the renin-angiotensin system in human mesangial cells was explored. the in vitro studies revealed that polymeric IgA from IgAN patients upregulated the gene expression of renin and MIF in human mesangial cells in a dose-dependent manner. These findings further support the notion that glomerular deposition of IgA is not only a pathological epiphenomenon of IgAN, but that polymeric IgA exerts a pathophysiologic effect on the mesangial cells leading to renal fibrosis.     

Immunological studies of IgA nephropathy in blacks reveal elevations of serum IgA2 as well as IgA1

Although IgA nephropathy (IgAN) is recognized worldwide as themost common primary glomerulonephritis, the prevalence of thisdisease among American blacks is strikingly low despite thefrequency of other renal disorders. We have previously describedthe clinical features of 27 black patients enrolled in a multicentreIgAN database; in this paper we report several immunologicalparameters of the disease in this population. Quantificationof serum immunoglobulins revealed significantly higher concentrationsof total IgA, IgAl and IgA2 (P=0.0001, 0.002 and 0.005 respectively)in the patients, but no significant increases in IgG or IgM.Examination of immunoglobulin synthesis by peripheral bloodlymphocytes indicated relatively few differences in the secretionof immunoglobulins by patients compared to healthy Americanblacks. The spontaneous production of total IgA, IgA1, and IgA2in patients was depressed compared to the control subjects (P=0.02,0.04, 0.03,), yet the ratio of IgA1:IgA2 was normal. Stimulationwith poke-weed mitogen enhanced secretion of immunoglobulinin both subject groups. However, a significantly greater IgA1:IgA2ratio was noted in the patients (P=0.002). Circulating immunecomplexes containing C3 and IgA as well as C3 and IgM were elevatedin the patients (P=0.0006, 0.0003 and 0.02, respectively). Theseimmunological aberrancies did not correlate with clinical manifestationsof disease. These data suggest the immune abnormalities of blackIgAN patients are similar to, but not identical with, thoseof white patients.     

Correlation between glomerular morphology and renal haemodynamic response to amino-acid administration in patients with IgA nephropathy

RATIONALE.: To establish relationship, if any, between renal morphologyand renal haemodynamic response to amino acids. DESIGN AND METHODS.: We investigated the correlation between renal haemodynamic regulationand morphology in a group of 15 patients with primary IgA nephropathy(IgAN) (age 26±2 years, BMI 24.4±1, GFR 64±5ml/min, RPF 377±34 mI/mm, FF 0.17±0.02). Twelvenormal subjects (age 30±3 years, BMI 24±1, GFR82±6 ml/min, RPF421±42 ml/min, FF 0.19±0.02)were studied as controls. IgA patients were divided into twogroups according to the histological staging of glomerular lesions:group I (n=7) stage II, and group II (n=8) stage III–IV. RESULTS.: In the basal state GFR was similar in the two groups and averaged64±9 and 64±6 ml/mm respectively. In contrast,FF was significantly lower in group II(0.14±0.01) (P<0.05)in comparison to group I (0.21±0.03) and controls (0.19±0.02).In order to evaluate the renal functional reserve, all studygroups underwent to an intravenous amino-acid infusion designedto increase plasma amino acid levels twofold (total from 2096±145to 4301±221 µmol/l in IgA nephropathy patientsand from 2272±83 to 3844±238 µmol/l in controls).In response to amino-acid infusion, GFR rose significantly ingroup I (GFR 20±2% and RPF 37±4% versus basal)and controls (GFR 20±2% and RPF 20±3% versus basal)(both P<0.01 vs basal). In contrast, in patients with moresevere glomerular lesions (group II) neither GFR nor RPF rosesignificantly (GFR –1±4% and RPF –8±6%versus basal) (P NS versus basal, P<0.01 versus group I andcontrols). CONCLUSIONS.: The data show that in IgA nephropathy: severe forms of glomerularlesions are associated with a complex alteration of glomerularhaemodynamic regulation, characterized by lower basal FF andloss of haemodynamic response to hyperaminoacidaemia.     

Long-term course of post-transplant mesangial IgA deposition: clinicopathologic study of nine cases

Abstract:  We conducted the present study to elucidate the fate of post-transplant mesangial IgA deposit under the long-term observation. Out of a total of 45 cases with post-transplant mesangial IgA deposition, nine cases with more than 4 yr of follow-up term were enrolled in this study, and clinicopathologic characteristics were described. The study included three men and six women with a mean age of 34.2 yr. The average observation time from the detection of mesangial IgA deposition was 6.1 yr. Three cases were categorized as recurrent IgA nephropathy, while six cases were classified into latent mesangial IgA deposition. One case with hypertension developed end-stage renal disease. The significant improvement in microscopic hematuria was observed in one recurrent IgA nephropathy case. Microscopic findings included mild mesangial stalk thickening in all but one case. IgA deposition demonstrated a significant decrease in three latent mesangial IgA deposition cases. No apparent reduction in dense deposit quantity was observed on electron microscopy. There was no association between clinicopathologic findings and the regimen of anti-immunosuppressive agents. This study showed the improvement of the disease activity did occur in both recurrent IgA nephropathy and latent mesangial IgA deposition. Further investigation of latent mesangial IgA deposition may present the important clue to the pathogenesis of IgA nephropathy.     

Impaired solubilization of glomerular immune deposits by sera from patients with IgA nephropathy

A study of the solubilization of glomerular immune deposits by sera from patients with IgA nephropathy is described. Renal biopsy specimens were obtained from patients with IgA nephropathy and other glomerular diseases. These specimens were incubated with fresh and heated sera from the same patients and healthy adults at 37 degrees C for one hour in plastic tubes. The sections were stained with fluorescein isothiocyanate (FITC)-labeled heavy chain specific anti-human IgA antiserum and then examined with a fluorescent microscope. It was shown that the solubilization of glomerular immune deposits by sera from patients with IgA nephropathy was significantly less than that by sera from healthy adults. It is possible that impaired solubilization of immune complexes in vivo could lead to the accumulation of glomerular immune deposits in patients with IgA nephropathy.     

Contribution of macromolecular IgA1 to IgA abnormality in IgA nephropathy

To evaluate the contribution of macromolecular IgA₁ to IgA abnormality in childhood IgA nephropathy, serum samples from 29 healthy children and 26 patients with IgA nephropathy in different age-groups (7–9, 10–12, and 13–15 years) were each separated by sucrose density gradient ultracentrifugation and assayed for IgA₁ using an enzyme-linked immunosorbent assay. IgA₁ in fraction I (sedimentation coefficient >11.4s) was significantly greater in patients 7–15 years of age (median 36.3–57.0 mg/dl) than in the age-matched controls (median 8.8–10.4 mg/dl). IgA₁ in fraction II (11.4–9.3s) was significantly greater in patients 10–15 years of age (median 46.7–52.6 mg/dl) than in the controls (median 27.8–35.5 mg/dl), and IgA₁ in fraction III (<9.3s) was significantly greater in patients 13–15 years of age (median 156.9 mg/dl) than in the controls (median 120.7 mg/dl). The ratio of IgA₁ in fractions I–III was higher in the patients of each age-group (median 0.233–0.314) than in the controls (median 0.067–0.082), while the ratio of IgA₁ in fractions II–III was not significantly high in patients 7–12 years old (median 0.268 to 0.318) compared with the controls (median 0.182–0.264). Thus, IgA abnormality in childhood IgA nephropathy would be better represented by an increase in macromolecular IgA₁ of >11.4s than by an increase in IgA₁ in fractions of 11.4–9.3s or <9.3s. Received: 8 December 1999 / Revised: 2 March 2000 / Accepted: 2 May 2000     

伴有新月体形成的原发性IgA肾病的临床与病理特点及预后分析

目的观察伴有新月体形成的原发性IgA肾病的临床、病理特点,分析其对激素及环磷酰胺治疗的反应。 方法收集包头医学院第一附属医院1997年8月至2015年04月收治的80例经肾活检确诊为原发性IgA肾病并伴新月体形成的患者,并依据新月体累及的肾小球比例进行分组,新月体占受累肾小球比例≥50% (A组) 24例;新月体累及的肾小球比例<50%(B组) 56例。肾小球系膜增生、肾小管间质病变采用R.Katafuchi标准积分量化。对两组的临床及病理特点进行比较。治疗方案：将A、B两组再分为单纯糖皮质激素(激素)治疗组,激素＋环磷酰胺治疗组,分别比较不同治疗方案对各组的疗效。A、B组各有24例患者接受了随访。应用SPSS软件进行统计学分析。 结果①临床方面：32例(40%)患者有镜下血尿＋蛋白尿,76例(95%)患者尿蛋白≥2 g/24 h,32例(40%)患者有肉眼血尿;水肿、高血压、肾功能异常者超过半数。A组尿蛋白量及血清肌酐明显高于B组(t＝1.890,t＝2.570; P<0.05),血清白蛋白及肾小球滤过率明显低于B组(t＝2.681, t＝3.014;P<0.05)。②病理方面：所有受累肾小球的新月体面积百分比为5.92%～88.9%,其中A组为52.6%～88.9%, B组为5.92%～48.9%;与B组比较A组肾小管间质损害更严重,两组比较差异有统计学(P<0.05)。③治疗情况：A组及B组经激素或激素＋环磷酰胺治疗后,尿蛋白定量均明显减少(P<0.05) ;单纯激素治疗后A组血清肌酐较治疗前有明显下降(t＝3.243,P<0.05)。随访2～4年时,A组8例患者出现血清肌酐升高,达透析指征,1例死亡;B组2例患者出现血清肌酐升高(1例原有轻度升高,1例新出现血清肌酐升高)。 结论IgA肾病患者随着新月体占受累肾小球比例的增加,肾小管间质病理损害及临床表现亦逐渐加重且预后不佳;激素治疗可减少伴有大新月体形成的原发性IgA肾病的蛋白尿并有可能改善其肾功能。     

IgA肾病患者IgA1糖基化异常及其致病机制

IgA肾病(IgAN)是导致终末期肾病最常见的原发性肾小球疾病。其病理特点为IgA1在肾小球系膜区沉积,IgA1分子的异常糖基化是导致IgAN发病的关键因素。多种与IgAN相关的基因位点已经被发现。这些基因编码的细胞因子参与了IgA1糖基化异常的发病机制。此外糖基化酶缺乏、分子伴侣甲基化异常都可能导致IgA1异常糖基化。异常糖基化的IgA1可通过自我聚集或形成免疫复合物沉积于系膜区,进而刺激系膜细胞增殖、分泌系膜基质、细胞因子、趋化因子、生长因子等,导致肾小球损伤。对IgA1异常糖基化的深入研究有助于了解IgA肾病的发病机制并提供新的诊断与治疗措施。     

IgA肾病合并高尿酸血症患者的临床病理分析

目的探讨IgA肾病合并高尿酸血症患者的临床及病理变化的特点,以期揭示IgA肾病伴有高尿酸血症的临床意义。方法回顾性分析2006年6月至2012年12月厦门大学附属中山医院肾内科收治的270例经肾活检确诊的原发性IgA肾病患者,依据血尿酸水平,将270例IgA肾病患者分为高尿酸血症组和尿酸正常组,测定记录所有患者的性别、发病年龄、收缩期血压、24 h尿蛋白定量、血尿酸、血肌酐、血白蛋白、血脂等临床指标,所有患者均进行肾脏病理检查并行Lee分级,统计分析2组的临床和病理特点,并对肾功能正常患者(135例)的病理指标进一步行亚组分析。结果IgA肾病患者高尿酸血症的患病率为25.19%,高尿酸血症组患者年龄、血白蛋白、血三酰甘油、血清总胆固醇水平与尿酸正常组比较,差异无统计学意义,患者男性比例、收缩期血压、24 h尿蛋白定量、血肌酐水平均高于尿酸正常组(P0.05),高尿酸血症组患者肾脏病理Lee分级严重的比例及发生肾小管间质病变、肾内动脉病变的比例均高于尿酸正常组(P0.05)。正常肾功能患者中,高尿酸血症组出现动脉壁肥厚等肾内动脉病变及肾小管间质慢性病变的比例亦高于尿酸正常组(P0.05)。结论 IgA肾病合并高尿酸血症患者与尿酸正常组患者比较,临床表现及肾脏病理损伤多较重,尤其对肾小管间质病变及肾内血管病变影响更明显,临床预后不佳,应予重视并及时有效地进行干预治疗。     

IgA肾病中医证型与免疫物质沉积关系探讨

目的探讨肾功能正常或代偿期的IgA肾病中医证型与肾小球免疫物质沉积之间的关系。方法36例。肾功能正常及代偿期的IgA肾病患者进行中医辨证分型,肾小球系膜区免疫物沉积度定量评分,分析中医证型与肾小球系膜区免疫物沉积类型及沉积度定量评分间的关系。结果肾功能正常及代偿期的IgA肾病患者,肺（脾）肾气虚型以3种免疫复合物沉积为主,气阴两虚型以4种免疫复合物沉积为主;在肾小球系膜区IgA沉积度定量评分比较中,肺（脾）肾气虚型IgA沉积度定量评分高于气阴两虚型,两证型之间有统计学差异（P〈0．05）;两证型在IgM、IgG、C3沉积度定量评分比较中无统计学差异（P〉0．05）。结论肺（脾）肾气虚型向气阴两虚型转变过程中,肾小球系膜区免疫复合物沉积种类增加;肺（脾）肾气虚型肾小球系膜区IgA沉积度高于气阴两虚型。     

No evidence for a role of cosmc-chaperone mutations in European IgA nephropathy patients

Background. Altered IgA1 galactosylation is involved in thepathogenesis of IgA nephropathy (IgAN). The galactosyltransferasecore-1 beta3-galactosyltransferase-1 (C1GALT1) and its chaperonecosmc are specifically required for O-galactosylation of theIgA1 hinge region. Mutations in the cosmc gene result in a secondaryloss of function of C1GALT1 with subsequent undergalactosylationof glycoproteins. Mosaic mutations of cosmc have been shownto result in autoimmune disease. We hypothesized that cosmcmutations might contribute to the altered IgA1 galactosylationin IgAN patients. Methods. We studied cosmc gene sequences in genomic DNA obtainedfrom male patients with biopsy-proven sporadic (n = 33) andfamilial IgAN (n = 6 patients from different families). To accountfor a potential mosaicism we sequenced cosmc in 10 differentperipheral blood mononuclear cell DNA clones of every patient.To specifically assess potential mosaic mutations in IgA-producingcells, cosmc mutations were also analysed in DNA isolated fromCD20+ B-lymphocytes from three male IgAN patients. Results. Despite our extensive genomic analysis, the data revealedno functionally relevant cosmc gene variants in sporadic orfamilial IgAN cases. A cosmc gene polymorphism, rs17261572,was identified in these IgAN patients in a similar frequencyas previously reported in healthy adults. A functional consequenceof this polymorphism has not yet been determined. Conclusion. Although decreased C1GALT1 activity has been implicatedin the IgAN pathogenesis and cosmc chaperone mutations can causeautoimmune disease, our data provide no evidence for a relevantrole of cosmc gene mutations in European patients with sporadicor familial IgAN.