Decreased IgA1 response after primary oral immunization with live typhoid vaccine in primary IgA nephropathy.

INTRODUCTION: Patients with primary IgA nephropathy (IgAN) have an increased level of immunological memory to certain parenteral recall antigens. We recently found a deficient IgA1 immune response after intranasal challenge with a neo-antigen: cholera toxin subunit B. In the present study, we assessed the specific IgA1 and IgA2 antibody response in plasma, peripheral blood cells and mucosal secretions after primary enteral immunization. METHODS: Twenty eight IgAN patients, 26 patients with non-immunological renal disease and 32 healthy subjects were immunized orally with three sequential doses of live, attenuated, Salmonella typhi Ty21a. The humoral immune response in body fluids and antibody synthesis by circulating B cells was assessed in specific ELISAs and ELIPSAs respectively. RESULTS: Oral immunization resulted in significantly (P<0.0001) increased IgM, IgG, IgA, IgA1 and IgA2 responses in all groups, both in plasma and in circulating B cells in vitro. The IgA1 response in plasma was significantly (P<0.05) lower in IgAN patients, while no significant differences in IgM (P=0.36), IgG (P= 0.79) or IgA2 (P=0.45) responses were found as compared with matched control groups. The amount of IgA1 synthesized by circulating B cells tended to be lower in IgAN patients. No significant IgA response after oral immunization with S. typhi Ty21a was found in saliva (P=0.11) or tears (P=0.10). CONCLUSIONS: These data suggest an IgA1 hyporesponsiveness in patients with IgAN that is not only apparent after primary challenge of the nasal-associated lymphoid tissue but also after presentation to the gut. Previous results after parenteral recall immunization may be explained by assuming that IgAN patients require more frequent and/or longer exposure to IgA1-inducing antigens on their mucosal surfaces before they reach protective mucosal immunity. As a consequence, overproduction of IgA1 antibodies occurs in the systemic compartment, accompanied by an increased number of IgA1 memory cells.     

O-glycosylation of serum IgA1 antibodies against mucosal and systemic antigens in IgA nephropathy

In IgA nephropathy (IgAN), serum IgA1 with abnormal O-glycosylation deposits in the glomerular mesangium. The underlying mechanism of this IgA1 O-glycosylation abnormality is poorly understood, but recent evidence argues against a generic defect in B cell glycosyltransferases, suggesting that only a subpopulation of IgA1-committed B cells are affected. For investigation of whether the site of antigen encounter influences IgA1 O-glycosylation, the O-glycosylation of serum IgA1 antibodies against a systemic antigen, tetanus toxoid (TT), and a mucosal antigen, Helicobacter pylori (HP), was studied in patients with IgAN and control subjects. Serum IgA1 was purified from cohorts of patients with IgAN and control subjects with HP infection and after systemic TT immunization. The IgA1 samples were applied to HP- and TT-coated immunoplates to immobilize specific antibodies, and IgA1 O-glycosylation profiles were assessed by binding of the O-glycan-specific lectin Vicia villosa using a modified ELISA technique. Although total serum IgA1 had raised lectin binding in IgAN, the O-glycosylation of the specific IgA1 antibodies to TT and HP did not differ between patients and control subjects. In both groups, IgA1 anti-HP had higher lectin binding than IgA1 anti-TT. This study demonstrates that IgA1 O-glycosylation normally varies in different immune responses and that patients produce the full spectrum of IgA1 O-glycoforms. IgA1 with high lectin binding was produced in response to mucosal HP infection in all subjects. The raised circulating level of this type of IgA1 in IgAN is likely to be a consequence of abnormal systemic responses to mucosally encountered antigens rather than a fundamental defect in B cell O-glycosylation pathways.     

T-cell homing receptor expression in IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA (pIgA). In IgAN, mucosal pIgA production is reduced while systemic production is increased, making the latter the likely source of mesangial pIgA, and suggesting a displacement of pIgA-producing cells from mucosal to systemic sites. Upon activation, lymphocytes migrate through the circulation up-regulating homing receptors (HR) which direct their return to appropriate effector locations. We investigated the HR expression of T-cell subsets in IgAN, healthy adults and membranous nephropathy (MN). METHODS: Peripheral blood cells were labelled for CD3, CD4 and CD8, and for L-selectin (naive cells), integrin alpha4beta1 (systemically homing cells) and integrin alpha4beta7 (mucosally homing cells) and analysed by flow immunocytometry. RESULTS: In IgAN, CD3 T cells displayed reduced L-selectin and increased alpha4beta1hi expression, with no difference in alpha4beta7. No abnormality of T-cell HR expression was found in MN. Both IgAN and healthy adults maintained their patterns of T-cell HR expression when studied again at a later time point, and the changes in IgAN were entirely accounted for by the CD4 T-cell subset with CD8 HR expression being normal. CONCLUSIONS: The consistently reduced L-selectin expression by CD4 T cells indicates increased activation of this subset in IgAN. These activated cells express alpha4beta1 rather than alpha4beta7, and therefore home to systemic effector sites. CD4 T cells regulate antibody production, including IgA. As pIgA is overproduced in systemic sites in IgAN, we hypothesize that these activated systemic homing CD4 T cells may direct the aberrant systemic pIgA production observed in IgAN.     

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.     

Immuno-histological analysis of dendritic cells in nasal biopsies of IgA nephropathy patients.

BACKGROUND: IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Intranasal vaccination of patients with IgAN has shown mucosal and systemic IgA hyporesponsiveness. Here, we investigated whether this IgA hyporesponse in IgAN patients can be explained by reduced numbers or altered subset distribution of dendritic cells (DCs) in nasal mucosa. METHODS: Eighteen IgAN patients and 18 healthy volunteers were recruited for this study. Nasal biopsies were taken, after local anaesthesia, from the lower edge of the inferior turbinate. Staining for different subsets of DCs was performed using specific monoclonal antibodies. To detect myeloid DCs, we used CD1a, DC-SIGN and blood dendritic cell antigen-1 (BDCA-1) as a marker and for plasmacytoid DCs we used BDCA-2. DC-cell numbers in the epithelium and in lamina propria were counted separately and expressed as positively stained cells per mm(2). RESULTS: Both myeloid and plasmacytoid DC could be demonstrated in nasal biopsies. Quantification showed that IgAN patients contained significantly more DC-SIGN-positive cells in the lamina propria compared to controls. In addition, in IgAN patients, we observed more CD1a-positive cells in the epithelium. No differences in BDCA-1 and BDCA-2-positive cells were found between patients and controls. The number of positively stained cells in the epithelial layer correlated strongly with the number of positively stained cells in the lamina propria. CONCLUSIONS: Patients with IgAN have higher numbers of CD1a-positive cells in the epithelial layer and more DC-SIGN-positive cells in the lamina propria. Therefore, the earlier observed IgA hyporesponsiveness in IgAN patients after mucosal vaccination cannot be explained by lower numbers of nasal DCs.     

Structural features of IgA molecules which contribute to IgA nephropathy.

IgA nephropathy (IgAN) is characterised by the mesangial deposition of polymeric IgA1 (pIgA1). pIgA1 production is reduced in the mucosal immune system in IgAN and increased in the marrow; this switch may be secondary to a defect in gammadeltaT cell control of IgA production. However this does not explain the mechanism by which pIgA1 deposits in the mesangium. There is no direct evidence that classical immune complex deposition occurs in IgAN and alternative mechanisms resulting from physicochemical abnormalities of the IgA1 molecule, particular altered glycosylation, have been proposed. IgA1 has a distinctive hinge region which is a site for O-glycosylation. There is reduced terminal galactose on the hinge region O-glycans of circulating IgA1 in IgAN, perhaps due to a defect in B cell beta1,3 galactosyltransferase. A concomitant O-glycan defect in mesangial IgA1 has not yet been proven. Altered hinge O-glycosylation may have substantial impact on the quaternary structure of the IgA1 molecule influencing its capacity to interact with matrix proteins, IgA receptors on mesangial cells and leucocytes, and complement; it may therefore play a key role in the pathogenesis of mesangial deposition of IgA1 and subsequent glomerular injury in IgAN.     

黏膜方对IgA肾病小鼠免疫学机制的影响

目的：探讨以中医和解清热立法组方的黏膜方治疗实验性IgA肾病的作用机制。方法：采用口服牛血清白蛋白（BSA）、尾静脉注射葡萄球菌肠毒素B（SEB）及腹腔注射免疫佐剂的方法诱发小鼠IgA肾病模型。随机分为正常组、模型组、中药组及对照组4组,观察治疗后各组尿蛋白、血清IgA及循环免疫复合物、肾组织肠组织IgA的表达、肾组织病理学的改变。结果：模型组小鼠尿蛋白和尿白蛋白较正常组增加,中药组较模型组尿蛋白降低;正常组肾脏无IgA沉积、肠黏膜IgA微弱表达,模型组肾脏有IgA沉积,其中主要是多聚IgA1（pIgA1）沉积、肠黏膜IgA强表达,各治疗组肾脏IgA沉积较模型组减弱、肠黏膜IgA强表达;各治疗组在肾组织中系膜细胞和系膜基质均较模型组明显降低（P〈0.01）,而中药组更优于对照组（P〈0.01）。结论：中药黏膜方能有效改善尿蛋白并抑制IgA沉积至肾小球系膜区,表明中医和解法能成为治疗IgA肾病的有效方法之一。     

Selective elevation of monomeric IgA1 in IgA nephropathy patients with normal renal function

The molecular form of the pathognomonic IgA in IgA nephropathy (IgAN) remains controversial. Because characterization of the molecular form of IgA molecules can lend insight into their origin (systemic v mucosal), we developed immunoassays to measure both total and J chain-containing (polymeric) IgA1 and IgA2. These assays were used to measure IgA in sera from two groups of IgAN patients (with normal or decreased renal function), as well as from a group of normal individuals. IgA1 levels were higher in both groups of patients with IgAN when compared with the controls. The elevation appeared to be restricted to non-J chain-containing (monomeric) IgA1 in patients with normal renal function, whereas polymeric IgA1 was also slightly elevated in patients whose renal function was diminished. While there were no significant differences between the groups in terms of the levels of total IgA2, the patient group with normal kidney function appeared to have lower levels of polymeric IgA2. The observation that the elevation in serum IgA appears to be restricted to the monomeric form of IgA1, at least when renal function is normal, implies a systemic origin of the pathognomonic IgA in IgAN and further suggests an abnormality in the regulation of IgA secretion by immunoglobulin-producing cells in bone marrow, the site of systemic IgA synthesis.     

Serum IgA and the production of IgA by peripheral blood and bone marrow lymphocytes in patients with primary IgA nephropathy: evidence for the bone marrow as the source of mesangial IgA

The origin of the mesangial IgA1 in primary IgA nephropathy (IgAN) is unknown. The bone marrow, the prime production site of plasma IgA in healthy humans, has not been previously investigated in patients with IgAN. In patients with IgAN, we found an increased percentage of IgA plasma cells containing IgA1 in the bone marrow (89.7% +/- 2.6% v 84.3% +/- 6.6%, P = 0.01), an increased percentage of serum IgA as IgA1 (92.2% +/- 4.9% v 80.2% +/- 6.6%, P less than 0.001), and an increased percentage of IgA1 of the IgA produced by peripheral blood lymphocytes in culture (75% +/- 16% v 54% +/- 19%, P less than 0.01). These findings are compatible with the bone marrow as production site of the mesangial IgA1. The data on IgA1 polymers are more difficult to interpret because their role in the pathogenesis of IgAN is still controversial. We found an increased concentration of both polymeric and monomeric IgA1 in the sera and supernatants of cultures of bone marrow of patients, although the ratio of polymeric to total IgA1 remained normal. In our opinion, the mucosa of the digestive tract is an unlikely source of the mesangial IgA because the absence of IgA2 in the deposits contrasts to the high percentage of IgA2 plasma cells in the intestinal mucosae. Moreover, in normal individuals, the digestive mucosae contribute very little to plasma IgA. Although the respiratory tract contains a higher percentage of IgA1 plasma cells, the 25% fraction of IgA plasma cells containing IgA2 is still very substantial. This percentage argues against the respiratory mucosae as a source of the mesangial IgA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Animal models of IgA nephropathy: Formulating therapeutic strategies

Summary: This review seeks to highlight those aspects of ongoing research with animal models that may facilitate development of effective and perhaps specific therapy of IgAN. Oral immunization is typically accompanied by a predominantly Th2 response; defects in the evolution of this typical response, instigated by cyclophosphamide and/or oestradiol, elicit IgAN in mice. The Th2 cytokines that predominate in orally immunized mice, and in patients with IgAN, promote abnormally glycosylated IgA, similar to the IgA in patients. Immune complexes prepared with IgA antibody bearing altered glycosyl residues show enhanced rates of glomerular uptake and altered rates of clearance from the circulation. When immune responses to infectious pathogens are localized to sites remote from a new infection with a serologically related organism, ‘misdirected’ responses permit pathogen replication and antigen production concomitant with strong host antibody responses. The resultant immune complexes elicit IgAN in mice. Similar ‘misdirected’ immune responses may arise in J chain-deficient subjects. Improved pharmacologic control of B cell trafficking and/or function could rectify these defects. Correction of deficiency in clearance of IgA immune complexes could benefit patients with secondary IgAN. Finally, manipulation of glomerular haemodynamics and/or production or response to intraglomerular cytokines and growth factors might ameliorate disease or forestall progression to glomerulosclerosis. Animal models have served as a conceptual springboard for a wide variety of clinical investigations, and in turn clinical information has guided the design and goal of experimental investigation. Hopefully, this synergy can continue, ultimately resulting in effective and specific therapy.     

IgA肾病诊疗进展

IgA肾病是全球最常见的原发性肾小球肾炎,亚洲人群中发病率高于其他人种。IgA肾病是目前导致终末期肾病的重要原因之一。临床上以血尿为特点,常伴随蛋白尿、高血压。其病理表现主要为IgA免疫复合物在肾小球系膜区的沉积、系膜细胞增生、毛细血管内皮细胞增生等。其发病机制可能为血液循环中半乳糖缺乏的IgA1增多,在內外界环境刺激下,产生过多的、能沉积于肾小球系膜区的免疫复合物。目前,对IgA肾病的诊断主要依靠病理检查。治疗方面,以肾素-血管紧张素系统阻断剂、控制血压为基础,恰当联合免疫抑制剂、细胞毒性药物、鱼油等或能延缓IgA肾病的进展。本文的目的是对IgA肾病的诊疗现状进行总结和分析,为临床工作及进一步科研提供指导和参考。     

Pathogenesis of idiopathic IgA nephropathy

Despite a prodigious amount of work on the physiology of IgA production in man, and many studies on the immunopathology of IgA nephropathy, ranging from the immunogenetics to the immune response to chemical characteristics of the IgA, we are hardly any nearer to defining the pathogenesis of this disease. One of the main changes in our understanding has been to recognise that the bone marrow, now known to produce normally one-third of the body's IgA, overproduces this immunoglobulin in IgA nephropathy. This alters the previous notion that IgA nephropathy was due simply to IgA production in the mucosa, although a mucosal component is not excluded. Certain characteristics of the IgA in the diseased kidney and the circulation have been defined: it is of subclass IgA1 and has a higher proportion of light chains and negative charge than in normal subjects. The specificities of the IgA, either in the kidney or in complexes, have not helped to clarify the pathogenesis. They have been found for a wide range of endogenous and exogenous antigens, suggesting that the antibody activity represents polyclonal B cell activation. These findings have not helped to confirm the prevailing theory that IgA nephropathy is an immune complex disease. Other theories put forward are that IgA nephropathy is an autoimmune disease, glomerular components or IgA itself being among the candidate antigens, or that there is primary dysregulation of the IgA immune system. At this stage of development in our understanding of this common nephropathy, it is important to guard against the assumption that idiopathic IgA nephropathy is one disease and is the result of a single pathogenetic mechanism.     

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.     

An increased polymeric IgA level is not a prognostic marker for progressive IgA nephropathy.

BACKGROUND: Elution of IgA from renal biopsies of patients with primary IgA nephropathy (IgAN) has suggested that mesangial IgA deposits are mainly multimeric in nature. This macromolecular IgA consists of dimeric and polymeric IgA and may be derived from the circulation. In children with IgAN, circulating macromolecular IgA levels correlate with bouts of macroscopic haematuria, but in adults a correlation with disease activity is less clear. Therefore, we have designed a novel method to assess the levels of polymeric IgA (pIgA) in sera from patients and controls. METHODS: A novel precipitation assay using recombinant CD89 was developed to measure pIgA. Polymeric IgA levels were measured in serum samples obtained from healthy volunteers (n = 21) and patients with IgAN (n = 51). Subsequently, serum pIgA levels were correlated with clinical parameters of disease. RESULTS: Serum pIgA levels were significantly increased in patients with IgAN. However, pIgA concentrations relative to total IgA were significantly lower in sera of patients with IgAN. No correlation was found between serum pIgA levels and clinical parameters of IgAN, such as decline of glomerular filtration rate, haematuria or proteinuria. CONCLUSIONS: Although absolute levels of serum pIgA are increased in patients with IgAN as compared with controls, levels of pIgA relative to total serum IgA are lower. No significant correlation was found between serum concentrations of pIgA and clinical parameters of disease. These data support the notion that it is not the size alone, but the physicochemical composition of the macromolecular IgA that is the key factor leading to mesangial deposition.     

IgA肾病患者扁桃体B1a细胞和IgA1阳性细胞表达及相关因素分析

目的 研究B1a和IgA1阳性细胞在IgA肾病患者扁桃体中的表达及B1a细胞与血尿、蛋白尿和病理Lee分级的关系。 方法 肾活检确诊为原发性IgA肾病及非肾炎慢性扁桃体炎患者各8例为对象,用免疫荧光法和激光共聚焦显微镜对其扁桃体组织进行B1a及IgA1细胞定位和定量计算,并按蛋白尿程度和Lee分级标准与IgA肾病组B1a细胞数量行统计学分析。 结果 B1a细胞主要分布在扁桃体生发中心和小结帽;IgA1细胞主要分布在上皮内、上皮下,以上皮和淋巴组织交界区为多。与慢性扁桃体炎组比较,IgA肾病组两种细胞表达明显增多（P < 0.01）,且呈正相关（r = 0.778,P = 0.023）。在血尿伴蛋白尿和Lee≥Ⅲ级组B1a细胞显著高于单纯血尿和Lee<Ⅲ级组（P < 0.05）。 结论 IgA肾病患者扁桃体中IgA1可能是B1a细胞分泌的。B1a细胞数量随着患者蛋白尿的出现和病理严重程度的加重而增加,可能在疾病发生和进展过程中起着重要的作用。     

Pathogenetic significance of aberrant glycosylation of IgA1 in IgA nephropathy

IgA nephropathy (IgAN), the most common form of primary glomerulonephritis worldwide, is defined by predominant IgA1 deposits in the glomerular mesangium. Among abnormalities of the IgA immune system reported so far in IgAN, aberrant O-linked glycosylation in the hinge region of IgA1 is the most consistent finding. IgA1 molecules bearing abnormal glycosylation have been found in serum, in tonsillar lymphocytes, and in eluate from mesangial deposits, and characterized by decreased O-linked N-acetylgalactosamine residues with or without alteration in the terminal sialylation of the O-linked sugars. IgA1 with incomplete galactosylation has a tendency to accumulate in glomerular mesangium by self-aggregation or immune complex formation. Glomerular mesangial cells exposed to immune complexes of these IgA1 can proliferate and secrete cytokines, chemokines, growth factors, and extracellular matrix components promoting inflammatory reactions in the glomeruli. Although genes encoding enzymes involved in the O-glycosylation process, such as C1GALT1, have been reported to be responsible for susceptibility to IgAN, recent evidence suggests that the abnormality is restricted to a small fraction of B cell populations and arises from dysregulated IgA1 production and secretion in mucosal immune system. This review will focus on and discuss the role of incompleteness of IgA1 O-galactosylation in the pathogenesis of IgAN and propose a possible mechanism in which abnormal IgA1 occurs in IgAN. Presented at the 37th Eastern Regional Meeting of the Japanese Society of Nephrology.     

黏膜方对IgA肾病大鼠异常糖基化IgA1及肾间质纤维化的干预及机制研究

目的:研究血清和肾组织中的异常糖基化IgA1水平与IgA肾病的间质纤维化程度的相关性;阐明黏膜方治疗IgA肾病的作用机制。方法:采用口服牛血清白蛋白、四氯化碳皮下注射和尾静脉注射脂多糖免疫复合法建立IgA肾病大鼠模型,随机分为正常组、模型组、中药组(黏膜方)及西药组(福辛普利钠)、中西医结合组(黏膜方+福辛普利),观察治疗后各组血清和肾组织异常糖基化的IgA1水平、血清IgA-纤维连接蛋白(IgA-FN)、肾组织转化生长因子-β1(TGF-β1)和α-平滑肌肌动蛋白(α-SMA)及其mRNA的表达量。结果:血清IgA-FN,中药组及中西医结合组低于模型组(P<0.001);血清异常糖基化IgA1量,中药组及西药组均低于模型组(P<0.05);肾组织中的异常糖基化IgA1水平,模型组高于正常组(P<0.05),各治疗组低于模型组(P<0.05);肾组织中TGF-β1mRNA及蛋白表达量模型组均显著高于正常组(P<0.01),各治疗组TGF-β1mRNA及蛋白表达均低于模型组(P<0.05);模型组α-SMAmRNA高于正常组(P<0.05),各治疗组低于模型组(P<0.001),模型组α-SMA蛋白表达阳性面积高于正常组(P<0.001),中西医结合组和西药组阳性面积低于模型组(P<0.05);肾组织α-SMAmRNA及蛋白表达与血清及肾组织中异常糖基化IgA1呈正相关(P<0.005);肾组织TGF-β1mRNA与血清及肾组织异常糖基化IgA1呈正相关(P<0.005)。结论:血清中异常糖基化IgA1与肾间质纤维化程度密切相关,黏膜方能减轻实验性IgAN大鼠血清及肾脏异常糖基化的IgA1水平,改善肾间质纤维化。     

Structural heterogeneity of glycans in IgA molecules: Implications for IgA nephropathy

Summary: The carbohydrate moieties on glycoproteins, including immunoglobulins (Ig), are involved in a broad spectrum of biological functions. As revealed by enzymatic or chemical removal of carbohydrate moieties, inhibition of glycosylation, or site-directed mutagenesis of asparagine residues to prevent N-linked glycosylation, carbohydrates on Ig have been shown to participate in binding, internalization and catabolism by hepatocytes or other cells, binding to Fc receptors on phagocytic cells, activation of complement, and opsonization. the structure of human IgA1 is unique among all Ig. the heavy chain contains a hinge region with a characteristic primary structure not seen in any other Ig, and which contains five short O-linked oligosaccharide side-chains composed of serine-linked N-acetylgalactosamine (GalNAc) and βl-3-linked galactose (Gal). Both of these monosaccharides may be sialylated. In contrast to ubiquitous N-linked side-chains, O-linked carbohydrate moieties are found rarely among human serum glycoproteins. We have demonstrated that IgA1 proteins from the sera of patients with IgA nephropathy (IgAN) are galactosylated to a lesser extent than those from healthy controls. Decreased content of Gal and decreased reactivity of IgA from IgAN patients with lectins specific for GalNAc indicate that these structural changes occur on glycans located in the hinge region of IgA1. Thus, in addition to rheumatoid arthritis, systemic lupus erythmatosus, inflammatory bowel disease and other disorders, IgA nephropathy may represent another example of a chronic disease in which aberrancies of carbohydrates are observed and may participate in aetiopathogenesis.     

An update on the pathogenesis and treatment of IgA nephropathy

Over the past two decades significant progress has been made in unravelling the complex pathogenesis of immunoglobulin A nephropathy (IgAN). Excess amounts of poorly galactosylated immunoglobulin (Ig)A1 in the serum appear to be the trigger for generation of glycan-specific IgG and IgA autoantibodies, resulting in the formation of circulating IgA immune complexes, which are pivotal to the development of nephritis. It remains unclear why there is an increase in poorly galactosylated IgA1 molecules in the serum in IgAN. One intriguing possibility is that this IgA is derived from displaced mucosal B cells, which have mis-homed from their mucosal induction sites to systemic sites, where they secrete polymeric, poorly galactosylated IgA directly into the circulation rather than onto mucosal surfaces. Lack of a clear appreciation of the origins of poorly galactosylated IgA1 and an incomplete understanding of immune complex formation have hampered development of specific therapeutic strategies to prevent mesangial IgA deposition. Clinicians have therefore been left to manage patients with generic therapies, mainly by control of blood pressure and renin-angiotensin blockade. A paucity of high-quality clinical trials has meant that evaluation of additional therapies, particularly immunosuppressive regimens, has been difficult and there remains a great deal of confusion over the optimum treatment of patients at high risk of progressive chronic kidney disease.