Glycosylation of circulating IgA in patients with IgA nephropathy modulates proliferation and apoptosis of mesangial cells

Abnormalities in circulating IgA1 have been demonstrated in patients with IgA nephropathy (IgAN). This study addresses the question of the functional significance of this alteration in creating mesangial injury. Biologic effects of selected IgA glycoforms isolated from serum of IgAN patients and controls and in vitro deglycosylated normal IgA were tested on cultured human mesangial cells (MC). IgA glycoforms, ranging from 250 to 500 kD molecular weight, were isolated by lectin affinity chromatography followed by HPLC. IgA and IgG content was measured by enzyme-linked immunosorbent assay. HPLC fractions were incubated with MC to evaluate proliferation and apoptosis rates and nitric oxide synthesis. Moreover, MC were conditioned with in vitro desialylated and degalactosylated normal IgA. Patients with IgAN displayed increased levels of IgA glycoforms exposing sialic acid in alpha2,6 linkage with N-acetylgalactosamine (Neu5Acalpha2,6GalNAc) (P < 0.02) and GalNAc (P < 0.05), indicating truncation of O-linked glycans of IgA1. Moreover, IgA glycoforms with increased exposure of mannose were observed (P < 0.03), suggesting a defective N-linked glycosylation. No modification in IgG glycosylation was detected. When incubated with MC, the IgA glycoforms isolated from patients with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, or mannose, significantly depressed the proliferation and increased the apoptotic rate and nitric oxide synthesis activity of cultured MC, in comparison with fractions isolated from controls. Similarly, in vitro desialylated and degalactosylated IgAs significantly depressed the proliferation and enhanced the apoptosis rates of MC. In conclusion, a significant modulation of several human MC functions exerted by serum IgA with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, and mannose residues isolated from IgAN patients is reported for the first time.     

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.     

Integrin expression and IgA nephropathy: in vitro modulation by IgA with altered glycosylation and macromolecular IgA

BACKGROUND: Signal transduction by mesangial cell (MC) integrins regulates cell growth and survival, extracellular matrix production, and organization. The aim of the study was to investigate human MC integrin modulation by differently glycosylated IgA and macromolecular IgA, which are thought to play a pathogenetic role in IgA nephropathy (IgAN). METHODS: MCs were incubated with purified human polymeric IgA, heat-aggregated IgA, IgA glycoforms generated by enzymatic hydrolysis of saccharide residues and serum fractions from IgAN patients, and controls isolated by lectin affinity and containing IgA with peculiar glycan patterns. Integrins were quantitated by flow cytometry. RESULTS: Cultured MCs highly expressed alphavbeta3 and some alpha3beta1; alphavbeta3 was up-regulated by matrix components (P < 0.02). In vitro desialylated and degalactosylated polymeric human IgA enhanced alphavbeta3 expression on cultured MCs (P < 0.001). Serum IgA glycoforms isolated from IgAN patients with high exposure of internal sugars, GalNAc, Neu5Ac2,6GalNAc, and Man enhanced alphav expression on cultured MCs more than healthy controls. CONCLUSIONS.: These data support the hypothesis that IgA glycation plays a role in modulating the cell-matrix interaction, and that this mechanism can be operating in IgAN.     

Light-chain composition of serum IgA1 and in vitro IgA1 production in IgA nephropathy.

A predominant expression of IgA1 in mesangial deposits, serum, and bone marrow culture supernatants has been shown in IgA nephropathy (IgAN). Furthermore an excess of lambda light chains in both mesangial deposits and serum IgA has been observed. However, the origin of mesangial IgA remains controversial. In the present study, we have examined the IgA1 light chain type in IgAN. Total IgA1, IgA1 kappa and IgA1 lambda were measured by ELISA in serum and culture supernatants from spontaneous and pokeweed-mitogen (PWM)-stimulated peripheral blood mononuclear cells (PBMC). We observed an increase in IgA and IgA1 serum concentrations in IgA nephropathy patients, with a ratio of serum IgA1 to total serum IgA identical between patients and controls. The concentration of serum IgA kappa did not differ between patients and controls but patients had a significantly higher concentration of serum IgA lambda. The IgA1 kappa to IgA1 lambda ratio was 1.06 +/- 0.42 in IgAN patients versus 1.55 +/- 0.36 in controls (P less than 0.01). By contrast, the concentrations of IgA1 kappa and IgA1 lambda in PBMC culture supernatants, both spontaneous and PWM-stimulated, were identical in patients and controls. Therefore, there is a specific increase in IgA1 lambda in patients' sera. This contrasts with the normal IgA1 production by PBMC, which are derived from mucosal-associated lymphoid tissues. This suggests that IgA isotypic deregulation is confined to the bone marrow compartment and is not a generalised defect of the IgA system.     

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)     

Charge-dependent binding of polymeric IgA1 to human mesangial cells in IgA nephropathy

BACKGROUND: IgA nephropathy (IgAN) is characterized by raised serum IgA1 and predominant mesangial IgA1 deposits of polymeric nature. The mechanism of polymeric IgA1 (pIgA1) deposition in the kidney mesangium is poorly understood in IgAN. It has been suggested that increased sialic acid content and anionic charge of the pIgA1 molecules may be operational in the IgA1 deposition in human mesangial cells (HMCs). The present study examined the binding of pIgA1 with different surface charges to HMCs. The binding characteristics of IgA1 to HMCs in the presence of polycation (poly-L-lysine) or polyanion (heparin) were also investigated. METHODS: IgA1 was purified in sera from patients with IgAN and from healthy controls by jacalin affinity chromatography. IgA1 was further separated into pIgA1 and monomeric IgA1 (mIgA1) by fast protein liquid chromatography (FPLC). pIgA1 or mIgA1 with different net charges on their surface were resolved by ion exchange chromatography (IEC) with a Mono Q column. The binding characteristics of pIgA1 and mIgA1 to HMCs in the presence or absence of polycation or polyanion were examined by flow cytometry. RESULTS: In patients with IgAN, the absolute amount of mIgA1 and pIgA1 is significantly higher than that of healthy controls (P < 0. 001). There was significant increase in binding of pIgA1 from patients with IgAN to HMC and cell lysate. pIgA1 that interacted strongly with the ion exchanger also bound more to HMCs when compared with IgA1 interacted weakly with the ion exchanger (P < 0. 001). The anionic charged pIgA1 from patients was significantly higher than that of healthy controls (P < 0.001). Preincubation with poly-L-lysine increased the binding of pIgA1 to HMCs. The binding of pIgA1 to HMCs was decreased by preincubation with heparin. CONCLUSIONS: The binding of IgA to HMCs is charge dependent. Polymeric IgA with the highest net negative charge binds more to HMCs. Preincubation with polyanion decreased the binding of polymeric IgA to HMCs. These results suggest an important role for anionic charge in IgA1 deposition onto the kidney mesangial cells.     

Mass spectrometry analysis of IgA1 hinge region in patients with IgA nephropathy

BACKGROUND: Physicochemical alterations of the IgA molecule are supposed to play a pathogenetic role in IgA nephropathy (IgAN). The present study was carried out to analyze the structural variety of O-glycans on the IgA1 hinge region in IgAN. Sera from 9 IgAN patients and 9 healthy controls were individually examined to evaluate the IgA1 content and binding lectins (jacalin and Helix aspersa), using enzyme-linked immunosorbent assay (ELISA) techniques. The IgA1 from pooled sera were separated by affinity chromatography (jacalin), and the fragment containing the hinge region was prepared by pyridylethylation and trypsin treatment. The IgA fragments containing the hinge glycopeptide (33-mer hinge peptide core (HP) + O-glycans) were separated by jacalin affinity chromatography. Because we used jacalin, we only analyzed the Gal-3GalNAc residue containing IgA. The molecular weight (MW) of the IgA1 fragments was estimated using an ion trap mass spectrometer equipped with an electrospray ion source (ESI/MS). RESULTS: IgA1 concentration in pathological sera was higher than in the control serum (p<0.01). Compared with controls, serum IgA1 from IgAN patients showed significantly greater binding to the 2 lectins, jacalin (p<0.01) and Helix aspersa (HA, p<0.001), which are specific for O-linked Gal-beta1,3-GalNAc and GalNAc, respectively. Analyses of pooled sera showed that the number of O-glycosidic chains was comparable in IgAN and normal sera. With regards to the individual residues, we found that IgAN sera contained less sugar and galactose and sialic acid moieties than sera from control subjects, was reduced in IgAN sera, while terminal N-acetylgalactosamine levels were higher when compared with normal serum.CONCLUSIONS: Abnormalities of hinge region O-linked glycans were confirmed using advanced spectrometry technology. The pathogenetic implications for aggregation and defective removal of IgA1 are discussed.     

骨形成蛋白7和转化生长因子β1在不同病理类型IgA肾病的变化

目的 观察转化生长因子β1（TGF-β1）和骨形成蛋白7（BMP-7）在不同病理类型IgA肾病的变化,并探讨其意义。方法 89例IgA肾病患者分成3组：A组为47例轻度系膜增生性IgA肾病;B组为29例中重度系膜增生性IgA肾病;C组为13例增生硬化或硬化性IgA肾病。检测患者的血压、尿蛋白量（24 h）、Scr和Ccr。免疫组化和ELISA方法测定患者肾组织冰冻切片及其血、尿中TGF-β1和BMP-7水平。计算患者病理切片硬化肾小球数、新月体数和间质纤维化面积百分比。结果 随着IgA肾病患者肾小球病变的加重,肾小管萎缩和肾间质纤维化增多,其血压、尿蛋白量（24 h）、Scr逐渐增加,除B、C两组间尿蛋白量（24 h）无显著差异外,其余各组间差异均有统计学意义（P＜0．05）。与A组比较,B组肾组织及血、尿TGF-β1明显增多,C组显著降低（P＜0．01）。肾组织冰冻切片及血、尿BMP-7随着肾脏病变的加重,水平逐渐下降（P＜0．01）;而且与Ccr呈正相关;与血压、Scr、尿蛋白量（24 h）、硬化肾小球数、新月体数、肾间质纤维化面积呈负相关。结论 TGF-β1在IgA肾病系膜增生严重时明显增加,肾脏广泛纤维化时明显降低,可能参与了IgA肾病肾间质纤维化的发生。BMP-7随肾脏病变的加重而明显降低,可能导致其抗肾纤维化作用减弱。     

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.     

Role of aberrant glycosylation of IgA1 molecules in the pathogenesis of IgA nephropathy

Studies of the properties of immune complexes (IC) in the circulation, urine, and mesangium of IgA nephropathy (IgAN) patients have provided data relevant to the pathogenesis of this disease. IC contain predominantly polymeric IgA1 molecules which are deficient in galactose (Gal) residues on O-linked glycan chains in the hinge region (HR) of their heavy (H) chains. As a result of this aberrancy, a novel antigenic determinant(s) involving N-acetylgalactosamine (GalNAc) and perhaps sialic acid (SA) of O-linked glycans is generated and recognized by naturally occurring GalNAc-specific antibodies. Thus, IC in IgAN consist of Gal-deficient IgA1 molecules as an antigen, and GalNAc-specific IgG and/or IgA1 as an antibody. IgG antibodies to Gal-deficient IgA1 are probably induced by cross-reactive microbial antigens; they are present at variable levels not only in humans with or without IgAN but also in many phylogenetically diverse vertebrate species. Incubation of human mesangial cells with IC from sera of IgAN patients indicated that stimulation of cellular proliferative activity was restricted to the large (>800 kDa) complexes. These findings suggest that experimental approaches that prevent the formation of large Gal-deficient IgA1-IgG IC may be applied ultimately in an immunologically mediated therapy.     

Humoral immunity against the proline-rich peptide epitope of the IgA1 hinge region in IgA nephropathy.

BACKGROUND: The human IgA1 hinge region is a unique mucin-like O-linked proline-rich glycopeptide, and its core peptide was found to be exposed aberrantly by the underglycosylation in IgA nephropathy (IgAN). We describe here the presence of humoral immunity against the IgA1 hinge peptide epitope in IgAN and evaluate the relationship between the underglycosylation of the IgA1 hinge region and humoral immunity. METHOD: The serum anti-IgA1 hinge peptide antibody (anti-alpha1HP ab) titre was measured and compared between the IgAN (n=37) and control groups (n=34) by enzyme-linked immunosorbent assay (ELISA) using a synthetic peptide corresponding to the human IgA1 hinge region, PVPSTPPTPSPSTPPTPSPS, as an antigen. Next, to evaluate the relationship between the underglycosylation of the IgA1 hinge region and the humoral immunity, the reactivity of the serum IgG from the patients with IgAN against monoclonal IgA1 which had been digested enzymatically to remove the carbohydrates from the IgA1 hinge region was measured by ELISA. RESULTS: The anti-alpha1HP ab titre was significantly higher in the IgAN group than in the control group (OD value: IgG class, 0.564+/-0.344 vs 0. 331+/-0.154, P=0.0014; IgM class, 0.272+/-0.148 vs 0.141+/-0.072, P<0.0001) and it was positive in approximately 40% of the patients with IgAN. In addition, the reactivity of the serum IgG from the IgAN patients against the monoclonal IgA1 was found to be increased as the carbohydrates were enzymatically removed from the IgA1 hinge region (when native=100; asialo, 122+/-9.5; agalacto, 167+/-11.5; naked, 188+/-3.9). CONCLUSION: These results suggested that the peptide epitope of the IgA1 hinge region which was aberrantly exposed by underglycosylation could induce the humoral immune response in IgAN.     

Leucocyte beta 1,3 galactosyltransferase activity in IgA nephropathy

BACKGROUND: Reduced galactosylation of the O-linked glycans of the IgA1 hinge region in IgAN has recently been described. To investigate the underlying defect resulting in this abnormality, we have measured the activity of beta 1,3 galactosyltransferase, the enzyme responsible for galactosylation of O-linked sugars. METHODS: A galactose-acceptor substrate was prepared from degalactosylated hinge region fragments of normal IgA1, and incubated with the T cell, B cell, and monocyte lysates from patients with IgAN and controls for acceptor regalactosylation. The extent of acceptor galactosylation was then measured with biotinylated Vicia villosa lectin (VV), which is specific for ungalactosylated moieties. Lectin binding of serum IgA from the same subjects was also measured. RESULTS: T cell and monocyte beta 1,3 galactosyltransferase activities did not differ between IgAN and control, but B cell lysates in IgAN showed significantly lower beta 1,3 galactosyltransferase activity than control (6.2 +/- 0.71 vs. 9.5 +/- 1.03 AU/microgram, P = 0.018). Furthermore, B cell beta 1,3 galactosyltransferase activity showed a negative correlation (r = - 0.87, P = 0.002) with VV lectin binding of serum IgA in IgAN, but not controls. CONCLUSIONS: These data indicate that altered IgA1 O- galactosylation in IgAN results from a B cell-restricted reduction of beta 1,3 galactosyltransferase activity. This enzyme defect may be a fundamental pathogenic abnormality in IgAN.      

A pathogenic role for secretory IgA in IgA nephropathy

IgA nephropathy (IgAN) is characterized by deposits of IgA in the renal mesangium. It is thought that deposits of IgA mainly involve high molecular weight (HMW) IgA1. However, there is limited information on the exact composition of HMW IgA in these deposits. In this study, we investigated the presence of secretory IgA (SIgA) in human serum and in the glomerular deposits of a patient with IgAN. Furthermore, we analyzed the interaction of SIgA with mesangial cells. With enzyme-linked immunosorbent assay, SIgA concentrations in the serum of IgAN patients and healthy controls were measured. Both patients and controls had circulating SIgA that was restricted to the HMW fractions. Patients tended to have higher levels of SIgA, but this difference was not significant. However, in patients with IgAN, high serum SIgA concentrations were associated with hematuria. Binding of size-fractionated purified serum IgA and SIgA to mesangial cells was investigated with flow cytometry. These studies showed stronger binding of SIgA to primary mesangial cells compared to binding of serum IgA. Importantly, after isolation and elution of glomeruli from a nephrectomized transplanted kidney from a patient with recurrent IgAN, we demonstrated a 120-fold accumulation of SIgA compared to IgA1 in the eluate. In conclusion, we have demonstrated that SIgA strongly binds to human mesangial cells, and is present in significant amounts in serum. Furthermore, we showed that SIgA is accumulated in the glomeruli of an IgAN patient. These data suggest an important role for SIgA in the pathogenesis of IgAN.     

Mesangial IgA1 in IgA nephropathy exhibits aberrant O-glycosylation: observations in three patients

BACKGROUND: In IgA nephropathy (IgAN), circulating IgA1 molecules display an abnormal pattern of O-glycosylation. This abnormality may potentially contribute to mesangial IgA1 deposition, but this is unproven because the O-glycosylation of mesangial IgA1 has not been analyzed. METHODS: IgA1 was eluted from glomeruli isolated from the kidneys of three IgAN patients obtained after nephrectomy or at postmortem. Serum from these patients, other patients with IgAN, and controls was subjected to the same treatment as the glomerular eluates. The O-glycosylation of eluted and serum IgA1 was measured by lectin binding using an enzyme-linked immunosorbent assay-based system. RESULTS: In all three cases, the lectin binding of IgA1 eluted from the glomeruli of IgAN patients was markedly higher than that of the serum IgA1 of the same individual, and also all but one of a series of serum IgA1 samples from other patients and controls. CONCLUSIONS: The higher lectin binding of glomerular compared with serum IgA1 suggests that O-glycosylated IgA1 molecules abnormally and selectively deposit in the kidney. These results provide the first evidence that mesangial IgA1 is abnormally O-glycosylated, and support a direct role for abnormal IgA1 O-glycosylation in the mechanism of mesangial IgA deposition in IgAN.     

Exposed peptide core of IgA1 hinge region in IgA nephropathy.

BACKGROUND: The human IgA1 hinge region is a very unique O-linked glycopeptide, and its sialylation and galactosylation recently were reported to be defective in the serum IgA1 derived from patients with IgA nephropathy (IgAN). This study was performed to examine the underglycosylation of the IgA1 hinge region and consequent exposure of the peptide core in IgAN. METHODS: A polyclonal antibody against a synthetic human IgA1 hinge peptide, PVPSTPPTP SPSTPPTPSPS, (anti-sHP ab) was raised in rabbits and shown specifically to recognize the IgA1 which was treated with neuraminidase, beta-galactosidase and alpha-N-acetylgalactosaminidase. The reactivity of the anti-sHP ab against the purified serum IgA1 was compared among the following three groups: 39 patients with IgAN, 30 patients with other renal diseases (ORD) and 21 healthy controls (HC) using an enzyme-linked immunosorbent assay. RESULTS: The reactivity was significantly higher in the IgAN group (mean +/- SD of OD 490 nm: 0.327 +/- 0.059) than in the ORD group (0.274 +/- 0.043, P=0.0002) and in the HC group (0.265 +/- 0.037, P<0.0001). No significant difference was observed between the latter two groups. The frequency of positive cases (> mean +/- 2SD of HC) was 46.2% (18/39) in the IgAN group, 6.7% (2/30) in the ORD group and 0% (0/21) in the HC group. CONCLUSIONS: It was suggested that the peptide core of the IgA1 hinge region is exposed aberrantly by a defective N-acetylgalactosaminylation and plays a possible role in the pathogenesis of IgAN.     

Differential effects of circulating IgA isolated from patients with IgA nephropathy on superoxide and fibronectin production of mesangial cells.

BACKGROUND: IgA nephropathy (IgAN) is characterized by predominant deposition of IgA in the glomerular mesangium. Serum IgA is often elevated in patients with IgAN, and it has been postulated that it is responsible for the mesangial lesions. However, the direct effect of circulating IgA on mesangial cells is not clear. METHODS: We investigated the effects of sera and IgA which were isolated from patients with IgAN on thymidine uptake, superoxide and fibronectin production and fibronectin mRNA expression of cultured rat mesangial cells, and we compared the findings to the effects of IgA isolated from patients with non-IgA mesangial proliferative glomerulonephritis (MsPGN) and normal controls. IgA was isolated with affinity chromatography using cyanogen bromide activated Sepharose 4B coupled to sheep antihuman IgA antiserum. RESULTS: Our results demonstrated that both sera and IgA from patients with IgAN dose-dependently increased mitogenesis of mesangial cells as measured by (3)H-labeled thymidine uptake. The thymidine uptake by sera and IgA isolated from patients with IgAN was significantly higher than that of sera and IgA isolated from patients with MsPGN and normal controls. Sera and IgA from patients with IgAN significantly enhanced superoxide and fibronectin production and fibronectin mRNA expression of mesangial cells. The superoxide and fibronectin production was also significantly higher as compared with patients with MsPGN and normal controls. CONCLUSIONS: Our results indicate that circulating IgA isolated from patients with IgAN is different from that of patients with MsPGN and normal controls and may potentially induce oxidative injury and production of extracellular matrix of glomerular mesangial cells in IgAN.     

Mycophenolate mofetil alleviates persistent proteinuria in IgA nephropathy

BACKGROUND: Mycophenolate mofetil (MMF) is increasingly used to treat primary glomerulopathies. Its effectiveness in IgA nephropathy (IgAN) remains unclear. METHODS: Forty IgAN patients with persistent proteinuria (>1 g/24 hours) despite conventional treatment with blockers of the renin-angiotensin system were randomized to receive MMF for 24 weeks (group 1) or continue conventional therapy (group 2), and followed for 72 weeks. The primary end point was reduction of proteinuria by 50% or more over entry level. RESULTS: Sixteen patients (80%) in group 1 versus six patients (30%) in group 2 reached the primary end point (P= 0.0019). Time-averaged change in proteinuria showed a significant decline in group 1, while control subjects displayed a modest rise (P= 0.003). By 72 weeks, the mean proteinuria was 62.0 +/- 7.7% (P= 0.003) and 120.5 +/- 14.1% (P= 0.351) that of the corresponding baseline value in group 1 and group 2, respectively. There was concomitant increase in serum albumin and decrease in serum IgA levels in group 1 but not group 2 patients. Baseline histologic grades, blood pressure control, and the rates of change in serum creatinine and creatinine clearance were not different between the two groups. Normalization in binding of polymeric IgA to cultured mesangial cells and serum interleukin-6 (IL-6) levels, which sustained to study end, was observed in group 1 but not group 2 subjects. CONCLUSION: In selected patients with IgAN, MMF is effective in lowering proteinuria and ameliorating some of the putative pathogenetic abnormalities.     

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.     

Deregulated platelet-activating factor levels and acetylhydrolase activity in patients with idiopathic IgA nephropathy.

BACKGROUND: Platelet-activating factor (PAF) is a phospholipid mediator with potent inflammatory activities. PAF stimulates IgA synthesis by B cells while IgA aggregates enhance PAF production by neutrophils and mesangial cells. These results led us to investigate blood PAF levels and plasma acetylhydrolase (AHA, the PAF catabolic enzyme) activity in patients with idiopathic IgA nephropathy (IgAN). METHODS: PAF and AHA levels were investigated using the platelet aggregation assay and degradation of (3)H-labelled PAF, respectively. The genotype of AHA with regard to the G994-->T mutation in exon 9 was assessed by an allele-specific polymerase chain reaction. RESULTS: Blood PAF levels were significantly (P:=0.003, Mann-Whitney U:-test) elevated in IgAN patients (50.6+/-6.8 pg/ml, n=33) compared with healthy controls (18+/-5 pg/ml, n=18). In contrast, plasma AHA levels were significantly (P:=0.0001, Mann-Whitney U:-test) reduced in patients with IgAN (61+/-2 nmol/ml/min, n=51) compared with healthy controls (78+/-4 nmol/ml/min, n=53). G994-->T transversion in exon 9 of AHA was not found in any of the IgAN patients. CONCLUSION: Elevated circulating levels of PAF in IgAN patients might result from an insufficient AHA probably related to environmental factors rather than genetic ones. The mechanism and the precise role of the PAF/AHA deregulation in IgAN patients remain to be clarified.     

Steroid therapy reduces mesangial matrix accumulation in advanced IgA nephropathy.

BACKGROUND: Steroid therapy for IgA nephropathy (IgAN) has been reported to ameliorate the long-term prognosis of IgAN, but its mode of action has not been fully elucidated. In this study, we examined the effect of steroids on glomerular morphological changes in IgAN. METHODS: We examined 16 patients with biopsy-proven IgAN (male/female =11/5, mean age 32.1 years) who were divided into prognosis groups according to criteria set by the Japanese Society of Nephrology. Initially, they received a loading dose of steroids, followed by a daily dose of 10-15 mg prednisolone. After 12 months, they underwent a second biopsy, and their histological and clinical features were examined. RESULTS: Before and after therapy, systolic blood pressure, diastolic blood pressure, serum creatinine and creatinine clearance all remained unchanged. However, urinary protein excretion decreased dramatically, from 1.6+/-1.7 to 0.4+/-0.2 g/day (P<0.005). Furthermore, computerized imaging revealed a significant reduction of the mesangial matrix index (MMI) from 14.5+/-5.2 to 9.5+/-3.6% (P<0.001). The numbers of sclerosing glomeruli did not change. CONCLUSIONS: Steroid therapy reduces mesangial matrix accumulation and reduces urinary protein excretion in advanced IgAN.