Anti-macrophage migration inhibitory factor reduces transforming growth factor-beta 1 expression in experimental IgA nephropathy.

BACKGROUND: In human glomerulonephritis, including immunoglobulin-A nephropathy (IgAN), glomerular expression of macrophage migration inhibitory factor (MIF) is found to correlate with progressive renal injury. We have shown previously that polymeric IgA is capable of inducing MIF production in cultured human mesangial cells, suggesting a role in inducing inflammatory injury in IgAN. Herein, we examined whether IgA deposition and the subsequent renal injury can be ameliorated with anti-MIF treatment in an experimental murine model of IgAN. METHODS: Glomerular IgA deposition was induced in 4-week-old BALB/c mice by intravenous injection of immune complexes consisting of dinitrophenyl-conjugated bovine serum albumin (DNP-BSA) and IgA MOPC-315 myeloma anti-DNP antibodies. To determine the therapeutic effect of anti-MIF, mice were given anti-MIF (5 mg/kg) or isotypic control antibody intravenously 2 h before the immune complexes administration. The mice were sacrificed 48 h after injection of DNP-IgA. Proteinuria and haematuria were determined and the kidneys were removed for histopathology, immunostaining and immunoblotting. The effect of exogenous MIF on production of TGF-beta 1 by cultured mesangial cells was also examined. RESULTS: IgA deposits were detected in glomeruli of all mice receiving the immune complexes while no glomerular deposit was detected in the control mice. Microscopic haematuria and mesangial hypercellularity were present in mice of the three experimental groups and were absent in the control group. Proteinuria was absent in all groups. Anti-MIF treatment also resulted in decreased renal expression of TGF-beta 1. Moreover, the reduction in TGF-beta 1 expression was confined mainly to glomerular mesangium. An in vitro culture experiment demonstrated that MIF increased TGF-beta 1 production in a time- and dose-dependent fashion. MIF-induced TGF-beta 1 synthesis was abolished by incubating cells with neutralizing antibody against MIF. CONCLUSIONS: Our finding shows that anti-MIF treatment can ameliorate kidney injury and reduce glomerular TGF-beta 1 expression in an experimental model of IgAN.     

Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy.

BACKGROUND: It has been suggested that polymeric IgA (pIgA) or IgA immune complexes play a significant pathogenic role in IgA nephropathy (IgAN). Macrophage migration inhibitory factor (MIF) shares many activities with other pro-inflammatory cytokines. In human glomerulonephritis, including IgAN, glomerular expression of MIF is found to correlate with progressive renal injury. We hypothesized that deposition of pIgA within the kidney may lead to enhanced synthesis of MIF by mesangial cells. METHODS: In this study we examined the effect of pIgA and monomeric IgA (mIgA) from randomly selected patients with IgAN in clinical quiescence on the gene expression and protein synthesis of MIF in cultured human mesangial cells (HMC). RESULTS: Both pIgA and mIgA from IgAN patients or matched healthy controls increased MIF gene expression and protein synthesis in a dose-dependent fashion. The magnitude of MIF protein induction by pIgA (100 microg/ml) was similar to that of tumour necrosis factor-alpha (TNF-alpha) at 10 pg/ml. In all subjects, the induction of MIF was higher for pIgA when compared with mIgA (P < 0.01). Furthermore, the up-regulation of MIF synthesis by either pIgA or mIgA was significantly higher in IgAN patients than in healthy controls (P < 0.05). Similarly, pIgA and mIgA were able to induce TNF-alpha gene expression and protein synthesis in mesangial cells. Incubation of mesangial cells with neutralizing antibody to TNF-alpha reduced the MIF synthesis induced by pIgA. CONCLUSION: We demonstrate that pIgA is capable of inducing MIF and TNF-alpha production in HMC, which may play a major pathogenic role in IgAN. Induction of MIF can be partially blocked by neutralizing antibody to TNF-alpha, suggesting the possibility that up-regulation of MIF synthesis in HMC is mediated via an amplifying proinflammatory loop involving TNF-alpha.     

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.     

Activation of tubular epithelial cells by mesangial-derived TNF-alpha: glomerulotubular communication in IgA nephropathy

BACKGROUND: IgA nephropathy (IgAN), characterized by mesangial IgA deposition, runs a variable clinical course with tubulointerstitial damage and renal failure in no less than 30% of patients. Histologically, IgA is rarely detected in renal tubules. The direct toxicity by IgA on renal tubules remains uncertain. We hypothesize that mediators released from human mesangial cells (HMC) triggered by IgA deposition may lead to activation of proximal tubular epithelial cells (PTEC). METHODS: The binding of IgA to PTEC or HMC was assessed by flow cytometry. IgA-HMC medium was prepared by collecting the spent medium in which growth arrested HMC were incubated with IgA isolated from patients with IgAN, healthy control subjects, or other nephritic control patients. PTEC was cultured with the IgA-HMC medium in the presence or absence of neutralizing antibodies to TNF-alpha, IL-1beta, TGF-beta, or PDGF. Gene expression and protein synthesis of TNF-alpha, MIF, or ICAM-1 by PTEC were determined by RT-PCR and ELISA, respectively. RESULTS: The binding of IgA isolated from patients with IgAN to PTEC was increased when compared to binding of IgA from healthy control subjects (P < 0.005). However, the binding to PTEC was less than one tenth that of HMC in IgAN. The binding to PTEC was not mediated through known IgA receptors, as shown by competitive binding assays and gene expression of the receptors. Despite the in vitro binding, PTEC cultured with isolated IgA exhibited no increased cell proliferation or enhanced synthesis of TNF-alpha, MIF, or sICAM-1. However, when PTEC were cultured with IgA-HMC medium prepared from IgAN patients, there was enhanced proliferation of PTEC (P < 0.001) and increased synthesis of TNF-alpha, MIF, and sICAM-1 when compared with PTEC cultured with IgA-HMC medium from control subjects (P < 0.001). The synthesis of MIF and sICAM-1 by PTEC cultured with IgA-HMC medium was reduced by neutralizing antibodies to TNF-alpha (P < 0.001) but not by neutralizing antibodies to IL-1beta, TGF-beta, or PDGF. CONCLUSION: Our finding implicates that TNF-alpha released from the mesangium after IgA deposition activates renal tubular cells. The glomerulotubular communication could play an important role in the pathogenesis of tubulointerstitial damage in IgAN.     

Novel mechanisms of tubulointerstitial injury in IgA nephropathy: a new therapeutic paradigm in the prevention of progressive renal failure

IgA nephropathy (IgAN) runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. Notably, renal progression correlates more closely with the severity of tubulointerstitial lesions than with the degree of glomerular lesions In IgAN. Mesangial IgA deposition induces local release of cytokines, complement, and angiotensin II leading to glomerular inflammation. It remains unclear how mesangial IgA deposition leads to tubulointerstitial injury in IgAN. Moreover, IgA deposits are rarely detected in renal interstitium in IgAN. We hypothesize that mediators released from mesangial cells triggered by IgA deposition leads to activation of proximal tubular epithelial cells. Our preliminary findings implicate a glomerulotubular cross talk with mediators released from the mesangium contributing to the pathogenesis of tubulointerstitial damage in IgAN. We have also found the expression of angiotensin II subtype-1 receptor or angiotensin II subtype-2 receptor in proximal tubular epithelial cells differs from that of mesangial cells. One potential therapeutic approach is to counterbalance the growth-stimulatory effects of angiotensin II through subtype-1 receptor in tubular epithelial cells by subtype-2 receptor-mediated apoptosis and growth inhibition. These novel findings may provide clinicians new therapeutic approach for selective blockade of the RAS in IgAN.     

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。     

Demonstration of secretory IgA in kidneys of patients with IgA nephropathy.

BACKGROUND: Recently we reported a possible role for secretory IgA (SIgA) in IgA nephropathy (IgAN), as suggested by increased serum levels in patients with active disease and accumulation of SIgA in a glomerular eluate. Therefore, we attempted to find support for these findings by analysis of the presence of SIgA in biopsies of IgAN patients. METHODS: Renal biopsies of 26 patients with biopsy-proven IgAN were analysed for the presence of SIgA and complement proteins. RESULTS: In 15% mesangial deposition of SIgA was demonstrated, using a specific staining for secretory component (SC) and colocalization with IgA. The presence of SIgA in these biopsies showed a strong correlation with deposition of mannose-binding lectin (MBL) and C4d. Moreover, we observed a strong colocalization between SIgA and MBL or C4d. This local complement activation has previously been linked to more severe renal disease. CONCLUSIONS: Therefore, these data provide additional evidence for a pathogenic role for SIgA in IgA nephropathy.     

Mesangial expression of angiotensin II receptor in IgA nephropathy and its regulation by polymeric IgA1

BACKGROUND: Enhanced gene expression for the renin-angiotensin system (RAS) is detected in glomerular mesangial cells in IgA nephropathy (IgAN). Preliminary studies showed a reduced glomerular gene expression of angiotensin II subtype 1 receptor (AT1R), suggesting a regulatory response to high intrarenal angiotensin II (Ang II) concentration in IgAN. METHODS: We examined the effect of polymeric IgA1 (pIgA1) from patients with IgAN on the expression of Ang II receptors in cultured human mesangial cells (HMC). RESULTS: Polymeric IgA1 from patients with IgAN down-regulated the expression of AT1R in HMC in a dose-dependent manner. When similar experiments were conducted with addition of an angiotensin-converting enzyme inhibitor (captopril) or an AT1R antagonist (losartan), there was a significant increase in the expression of AT1R. Blockade of Ang II with captopril or losartan alone resulted in a stepwise increase of AT1R in cultured HMC. Down-regulation of Ang II subtype 2 receptor (AT2R) was not observed in HMC cultured with pIgA1 from patients with IgAN. The acute suppressive effect of pIgA1 from IgAN on the expression of AT1R was confirmed in HMC incubated with IgA isolated from 15 IgAN patients, 15 healthy subjects, and other glomerulonephritides control subjects. Reduced glomerular expression of AT1R (but not AT2R) was also demonstrated in renal biopsies from patients with IgAN. CONCLUSION: Our findings demonstrate an altered AT1R expression in HMC in response to raised intrarenal Ang II in IgAN. Our in vitro studies also support that an imbalance of AT1R and AT2R activity in HMC following exposure to pIgA plays a significant pathogenetic role in the inflammatory injury in IgAN.     

Intrarenal synthesis of IL-6 in IgA nephropathy

Summary: Recent in vitro studies have shown the synthesis of interleukin-6 (IL-6) in glomerular mesangial and epithelial cells, and suggested the involvement of IL-6 in mesangial proliferative glomerulonephritis. However, the expression site of IL-6 mRNA in renal tissue of IgA nephropathy (IgAN), the most common chronic mesangial proliferative glomerulonephritis, remains obscure. to localize IL-6 mRNA in renal biopsy specimens of IgAN, we used nonradioactive in situ hybridization (ISH) developed in our laboratory, sensitive in detecting individual cells positive for a specific mRNA. In some sections, periodic acid-Schiff staining was performed after ISH in order to identify the topographical relation between IL-6 mRNA positive cells and glomerular basement membrane and mesangial area. In situ hybridization for IL-6 mRNA and immunohistochemistry for CD3 and CD68, markers for lymphocytes and monocytes, respectively, were also performed on serial sections to examine the contribution of infiltrated mononuclear cells to cells positive for IL-6 mRNA in glomeruli. Glomerular resident cells, including glomerular mesangial and epithelial cells and cells of Bowman's capsule, as well as tubular epithelial cells and infiltrated mononuclear cells expressed IL-6 mRNA. We also compared the localization of IL-6 mRNA and protein and showed different distribution between the gene product and protein. the expression of IL-6 mRNA correlated with the degree of mesangial cell proliferation and tubulointerstitial changes. Our results indicate that IL-6 is synthesized in renal tissues of IgAN and suggest that the increased IL-6 expression may be important in the pathogenesis of IgAN.     

IgA serology in recurrent and non-recurrent IgA nephropathy after renal transplantation

BACKGROUND: This study investigated whether abnormal circulation of macromolecularIgA and IgA with altered glycosylation or electrical chargeplays a role in the recurrence of IgA nephropathy (IgAN) aftertransplantation. STUDY DESIGN: A total of 92 renal transplant patients were enrolled; 52 IgANpatients and 40 with other non-IgAN. The IgAN group included10 patients showing IgA mesangial deposits in the grafted kidneys(recurrent group) and 10 who did not (immunohistochemicallyproven non-recurrent group). In addition another 22 IgAN transplantpatients were clinically free of recurrent disease. METHODS: The analyses included macromolecular IgA (IgAIC) detected bythe conglutinin assay (K), heavy IgA precipitated in 2.5% polyethyleneglycol (PEG), IgA-fibronectin aggregates (IgA/F Aggr), mixedIgA/IgGIC, IgA binding to mesangial matrix components (fibronectin,laminin, type IV collagen) or polycations (poly-L-lysine) andIgA with altered glycosylation (Jacalin-binding assay). RESULTS: After transplantation, IgAN patients displayed significantlyhigher mean levels for each variable measured than non-IgAN(ANOVA, P <0.05). By stepwise regression analysis, the bindingof IgA to fibronectin had the highest coefficient. By comparingdata in recurrent and clinically non-recurrent IgAN, we observedthat two groups could be distinguished by the results of thetwo assays for macromolecular IgA (conglutinin IgAIC and IgA-fibronectinaggregates) and IgA with increased affinity for type IV collagen(P <0.05). When the selected group of immunohistochemicallyproven non-recurrent IgAN was compared to the recurrent one,a statistically significant difference was found only for thebinding of IgA to type IV collagen (P<0.05). Data from thistest were significantly related with proteinuria (P<0.05)and microscopic haematuria (P <0.04). CONCLUSION: Even though the IgA serology of renal transplant IgAN patientsshows peculiar features and recurrent and non-recurrent IgANdiffer in many aspects, the prevalence of positive data in thetwo groups had no predictive value. This suggests that the recurrenceof IgAN is modulated by factors affecting the interaction betweencirculating abnormal IgA and mesangial cells and/or matrix.     

Differential glycosylation of polymeric and monomeric IgA: a possible role in glomerular inflammation in IgA nephropathy

IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1 (pIgA1) and complement. Complement activation via mannose-binding lectin and the lectin pathway is associated with disease progression. Furthermore, recent studies have indicated a possible role for secretory IgA. IgAN is associated with abnormalities in circulating IgA, including aberrant O-linked glycosylation. This study characterized and compared functional properties and N-linked glycosylation of highly purified monomeric IgA (mIgA) and pIgA from patients with IgAN and control subjects. Total serum IgA was affinity-purified from patients (n = 11) and control subjects (n = 11) followed by size separation. pIgA but not mIgA contained secretory IgA, and its concentration was significantly higher in patients with IgAN than in control subjects. Both in patients with IgAN and in control subjects, IgA binding to the GalNAc-specific lectin Helix Aspersa and to mannose-binding lectin was much stronger for pIgA than for mIgA. Furthermore, binding of IgA to mesangial cells largely was restricted to polymeric IgA. Binding of pIgA to mesangial cells resulted in increased production of IL-8, predominantly with IgA from patients with IgAN. Quantitative analysis of N-linked glycosylation of IgA heavy chains showed significant differences in glycan composition between mIgA and pIgA, including the presence of oligomannose exclusively on pIgA. In conclusion, binding and activation of mesangial cells, as well as lectin pathway activation, is a predominant characteristic of pIgA as opposed to mIgA. Furthermore, pIgA has different N-glycans, which may recruit lectins of the inflammatory pathway. These results underscore the role of pIgA in glomerular inflammation in IgAN.     

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.     

Abnormalities of IgA1 production in IgA nephropathy

SUMMARY: IgA nephropathy (IgAN) is characterized by the mesangial deposition of polymeric IgA1 (plgA1). the original view that this plgA1 is derived from the mucosal immune system can no longer be sustained. Studies of duodenal mucosa and marrow indicate increased production of plgA1 in the marrow and decreased production in the mucosa. These changes are consistent with immunization studies showing exaggerated and prolonged plgA responses to systemic immunization, and reduced mucosal responses to mucosal neoantigens. However, the IgA1 and IgG systemic responses to mucosal antigen are increased in IgAN, a finding consistent with impairment in oral tolerance, the process by which systemic immune responses, to mucosal antigen challenge are normally suppressed. Both IgA1 production and the induction of oral tolerance are under T-cell control. T-cell populations involved in these processes include γδ T cells, Tr cells and T-helper (Th)3 cells; cytokines with a key role in the control of IgA production include interleukin (IL)-10 and transforming growth factor (TGF)-β. There is evidence of abnormal γδ T-cell V region usage in both mucosa and marrow in IgAN. Increased expression of relevant cytokines has also been reported in circulating T cells in IgAN. the increased O-glycosylation of circulating IgA1 in IgAN may also be further evidence of a shift in the production of mucosal-type plgA1 from the mucosa to marrow. These findings suggest that the specific lymphocyte homing mechanisms that normally maintain oral tolerance and control the site of IgA production require further study in IgAN.     

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.     

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。     

Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the renin-angiotensin system

The effects of polymeric IgA1 (pIgA1) and monomeric IgA1 (mIgA1) from patients with IgA nephropathy (IgAN) on the renin-angiotensin system (RAS) and TGF-beta synthesis were examined in cultured human mesangial cells (HMC). Both pIgA1 and mIgA1 induced renin gene expression in HMC, in a dose-dependent manner. Similar findings were observed for TGF-beta gene and protein expression. The values measured in HMC incubated with pIgA1 were significantly higher than those in HMC incubated with equivalent amounts of mIgA1. When similar experiments were performed with the addition of either captopril or losartan, there was a significant increase in the renin gene expression by HMC, whereas the synthesis of TGF-beta was markedly reduced. The TGF-beta signal transduction pathways in HMC were studied by measuring the receptor-regulated Smad proteins (Smad 2 and 3) and common-partner Smad proteins (Smad 4). pIgA1 from patients with IgAN upregulated Smad activity in HMC, and the activity observed in HMC that had been preincubated with pIgA1 was readily suppressed with optimal concentrations of captopril or losartan. The effects of pIgA1 on the RAS were further examined in HMC incubated with IgA isolated from 30 patients with IgAN, 30 healthy subjects, and disease control subjects with other diseases. pIgA1 induction of angiotensin II or TGF-beta synthesis in HMC was significantly greater with preparations from patients with IgAN, compared with healthy or disease control subjects. The findings support a pathogenetic role of pIgA1 in IgAN through upregulation of the RAS and TGF-beta, leading to chronic renal failure with renal fibrosis.     

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。     

Tubular expression of angiotensin II receptors and their regulation in IgA nephropathy

Enhanced renal expression for the renin-angiotensin system (RAS) is detected in IgA nephropathy (IgAN). Previous data showed an altered glomerular expression of angiotensin II type 1 receptor (AT1R), suggesting a regulatory response to high intrarenal angiotensin II (Ang II) concentration in IgAN. In this study, the expression and regulation of Ang II receptors were examined in human proximal tubular epithelial cells (PTEC) in IgAN. Tubular expression of AT1R and Ang II type 2 receptor (AT2R) was increased in IgAN. In vitro culture experiment showed that the upregulation of Ang II receptors was not due to the direct effect of IgA but the indirect effect after IgA deposition on human mesangial cell. When PTEC were cultured with conditioned culture medium from human mesangial cells activated with IgA, Ang II production was upregulated, leading to inflammation and apoptosis via the AT1R and AT2R, respectively. Sequential expression of Ang II receptors determined the injury of PTEC induced by mediators in the conditioned medium. The initial interaction between Ang II and AT1R activated both protein kinase C and mitogen-activated protein kinase pathways, leading to inflammatory responses. This early AT1R-dependent event was followed by upregulation of AT2R expression and continued Ang II release. The interaction between Ang II and AT2R subsequently led to expression of cleaved poly[ADP-ribose] polymerase through downregulation of the mitogen-activated protein kinase pathway. The data suggest that appropriate control of Ang II receptor activities in PTEC may ameliorate tubulointerstitial injury in IgAN.     

The level of serum secretory IgA of patients with IgA nephropathy is elevated and associated with pathological phenotypes.

BACKGROUND: Mucosal infection associated episodic macroscopic haematuria is observed in many patients with IgA nephropathy (IgAN), however, the mechanism has not been elucidated. Recent study suggested that secretory IgA (SIgA) might play an important role in the pathogenesis of IgAN. The aim of this study is to investigate the level of serum SIgA and the deposition of SIgA in glomeruli in IgAN patients with different pathological phenotypes. METHODS: The levels of serum SIgA were detected in 57 patients with IgAN and 48 normal controls. The associations between the levels of SIgA and the pathological phenotypes of IgAN as well as clinical parameters were investigated. Frozen renal sections from 34 of the 57 patients without IgM deposition were immunofluorescence stained and examined by confocal microscopy to detect the co-deposition of IgA and secretory component (SC). The association between deposition of SIgA and the level of serum SIgA was analysed. RESULTS: The level of serum SIgA in patients with IgAN was significantly higher than that of normal controls. The level of serum SIgA in patients with focal proliferative sclerosing IgAN (fpsIgAN) was much higher than that in patients with mild mesangial proliferative IgAN (mIgAN) (P<0.001). The level of serum SIgA correlated with the level of serum creatinine (R=0.509, P<0.001), degree of proteinuria (R=0.643, P<0.001) and creatinine clearance (R= -0.454, P=0.002) in patients with IgAN. Significant co-deposition of SC and IgA were found in 11 of the 34 patients. Although the level of serum SIgA in patients with SC deposits was higher than those without SC deposits, the difference was not significant. CONCLUSIONS: It was concluded that mesangial IgA, at least partly, was originated from mucosal immune sites. The levels of serum SIgA were significantly increased in patients with IgAN and were closely associated with pathological phenotypes.     

Immunological aspects of IgA nephropathy

Summary: IgA nephropathy (IgAN) is one of the most common primary renal diseases, and can be readily diagnosed by finding glomerular IgA deposits as either the dominant or codominant immunoglobulin on immunofluorescence microscopy. Despite some contradictory results about the nature and origin of IgA, it is generally accepted that the deposited IgA is polymeric and belongs to the IgA, subclass and systemic compartment is the source of circulating polymeric-IgA in IgAN. Because IgAN presents with asymptomatic microscopic haematuria or with episodic gross haematuria following upper respiratory and gastrointestinal disturbance, various environmental respiratory or gastrointestinal infectious agents and dietary antigens are suggested. Until now, however, it has not been possible to unequivocally identify specific antigens that are responsible for the formation of mesangial IgA deposits in patients with IgAN. Overproduction or delayed clearance of IgA as observed in patients and in animal models and in those processes, polyclonal stimulation of immunoglobulin production, with structural abnormalities of IgA, seems to play an important role. The mechanism responsible for the mesangial deposition of IgA is still unclear. The codeposition of IgA, C3 and properdin without Clq and C4 suggested a possible activation of the alternative pathway by IgA-containing immune complexes. To sum up, in IgAN the predominant antibody appears to be composed of polymeric-IgA₁ originating in the systemic compartment. The deposition of polymeric-IgA₁ in the mesangium and the activation of the alternative pathway of complement are probably crucial in the induction of the inflammatory lesions in the glomeruli and the development of haematuria in IgAN.