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

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

Defective immunoglobulin A (IgA) glycosylation and IgA deposits in patients with IgA nephropathy

Defective glycosylation and immune complex (IC) formation may be of primary importance in immunoglobulin A nephropathy (IgAN) pathogenesis. The aim of this study was to determine whether defective IgA1 glycosylation might support renal deposition of IgA and disease activity. IgA was isolated from the serum of 44 IgAN patients and 46 controls and glycosylation analysed by ELISA using glycan‐specific lectins. IgA was measured by immunodiffusion and immune complexes by ELISA. IgA subclasses in IC deposits in kidney glomeruli were identified by immunohistochemical methods. A significant increase in N‐acetylgalactosamine (GalNAc) in terminal position (p = 0.02) observed in some of the IgAN patients, became more pronounced when sialic acid was removed from IgA1, indicating enhanced expression of α‐2,6‐sialyltransferase in patients compared with controls (p < 0.0001). Patients with defective galactosylation had lower serum IgA than other IgAN patients (p = 0.003). IgAN patients with both IgA1 and IgA2 glomerular deposits (21.7%) had increased GalNAc in terminal position (p = 0.003). Taken together, our results show that increased IgA glycosylation in IgAN associates with low levels of IgA, concomitant IgA1 and IgA2 glomerular deposits and poor clinical outcome.     

血清IgA、C3及IgA/C3比值在IgA肾病诊断中的应用价值

目的：探讨原发性IgAN和非IgAN原发性肾小球肾炎患者血清IgA、C3水平和IgA/C3比值的差异及与病理Lee氏分级的相关性。方法：选择上海交通大学医学院附属新华医院肾脏内科经肾穿刺组织活检确诊为原发性IgAN患者167例与非IgAN原发性肾小球肾炎患者105例,以透射免疫比浊法测定其血清IgA和C3浓度,按Lee氏分级标准评估IgAN的病理分级。结果：①原发性IgAN患者与非IgAN原发性肾小球肾炎患者血清IgA水平分别为[（2.98±1.27）vs（2.15±0.88）g/L,P〈0.01];血清C3水平分别为[（1.11±0.27）vs（1.12±0.29）g/L,P〉0.05];IgA/C3比值分别为[（2.83±1.34）vs（2.05±1.12）,P〈0.01];②Lee氏分级为Ⅰ和Ⅱ级与Lee氏分级为Ⅲ、Ⅳ、Ⅴ级的IgAN患者血清IgA水平分别为[（2.73±0.95）vs（3.12±1.41）g/L,P〈0.05];血清C3水平分别为[（1.94±0.32）vs（1.10±0.24）g/L,P〉0.05];IgA/C3比值分别为[（2.70±1.45）vs（2.90±1.26）,P〉0.05]。③IgAN患者不同临床起病表现组间IgA、C3水平和IgA/C3比值的差异均无统计学意义。结论：血清IgA水平及IgA/C3比值可作为鉴别IgAN与非IgAN的参考指标,血清C3水平的降低程度与IgAN患者病理严重程度相关。     

Increase in B-cell-activation factor (BAFF) and IFN-gamma productions by tonsillar mononuclear cells stimulated with deoxycytidyl-deoxyguanosine oligodeoxynucleotides (CpG-ODN) in patients with IgA nephropathy

IgA nephropathy (IgAN), the most common form of primary glomerulonephritis, is recognized as a tonsil-related diseases since it often gets worse after and/or during acute tonsillitis and the disease progression is often prevented by tonsillectomy. Although several reports showed an increase in IgA production of tonsillar mononuclear cells (TMCs), its mechanism has not yet been fully clarified. Recently, B-cell-activation factor (BAFF), which stimulates B-cell proliferation and immunoglobulin production, was identified. Unmethylated deoxycytidyl-deoxyguanosine oligodeoxynucleotide (CpG-ODN), which is able to mimic the immunostimulatory activity of microbial DNA, is known to be involved in the production of immunoglobulins and some cytokines. In this study, we focused on roles of BAFF and IFN-gamma in IgA production of TMCs stimulated with CpG-ODN in IgAN patients. Two-color flow cytometric analysis revealed that the intercellular expression of IFN-gamma on the T-cells freshly isolated from tonsils was significantly higher in IgAN patients than in non-IgAN patients (p=0.032). The spontaneous productions of IgA and IFN-gamma of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p=0.023 and p=0.02). Under stimulation with CpG-ODN, the productions of IgA, BAFF and IFN-gamma of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p=0.013, p=0.005 and p=0.039). The IgA production of TMCs stimulated by CpG-ODN was inhibited by the treatment with anti-BAFF antibody and/or anti-IFN-gamma antibody. Under stimulation with IFN-gamma, the BAFF expression on the CD1c cells and the BAFF production of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p=0.004 and p=0.042). These data suggest that hyper-immune response to microbial DNA may be present in IgAN patients and may lead to hyperproduction of BAFF up-regulated by IFN-gamma, resulting in hyperproduction of IgA in IgAN patients.     

Anti-vascular endothelial cell antibodies in patients with IgA nephropathy: frequency and clinical significance

This study examined the frequency of anti-vascular endothelial cell (VEC) antibodies (Ab) in 72 patients with IgA nephropathy (IgAN), and their possible relationship to clinical and histological parameters of the disease. An enzyme immunoassay was developed to measure the binding of sera to endothelial cells grown to a confluent monolayer. Thirty-two percent of IgAN patients had serum anti-VEC activity as compared to 4% of controls (P = 0.004) and 9% of patients with other primary glomerulonephritis (P = 0.017). This was shown to be due to anti-HLA class I Abs in 6 of the 23 IgAN patients, and in the 1 control positive for anti-VEC activity. Hence 17 IgAN patients had anti-VEC Abs, predominantly of the IgA subclass. Stimulation of the endothelial cells with interferon-gamma and interleukin 1 did not increase the binding of these Abs. There was no correlation with circulating immune complex (IC) levels, and removal of ICs in positive sera by ultracentrifugation did not decrease anti-VEC binding. Significant correlations were found between anti-VEC Abs and proteinuria greater than 1 g/day (P = 0.044), as well as IgA anti-VEC Abs and C3 or IgA deposition in renal arterioles (P = 0.048). These IgA Abs may be an important marker of pathogenetic activity in IgAN.     

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

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

Variants of the ST6GALNAC2 promoter influence transcriptional activity and contribute to genetic susceptibility to IgA nephropathy

IgA nephropathy (IgAN) is a polygenic disorder. Increasing evidence has implicated that aberrant glycosylation of IgA1 molecules, including alpha2,6 sialic acid defects, are involved in the pathogenesis of IgAN. In the present study, we designed an association study to investigate polymorphisms of two important genes, ST6GALNAC2 and NEU1, which are involved in the sialylation of the IgA1 molecule, in the susceptibility to IgAN. A total of 670 patients with histologically proven IgAN and 494 healthy controls were enrolled. Screening of SNPs in the coding and promoter regions of the ST6GALNAC2 and NEU1 genes was performed by sequencing. ST6-SNP1 (c.-988A>G), ST6-SNP2 [rs3840858:D>I(CGGC), c.-450_-449insCGGC], ST6-SNP3 (rs1867561:C>G, c.-135C>G), and ST6-SNP7 (rs2304921:G>A, c.186+12G>A) in the ST6GALNAC2 gene were selected as tagging SNPs. Functional evaluations of targets were assayed by luciferase activity. The alpha2,6 sialic acid contents of serum IgA1 in 497 patients were analyzed. Our results demonstrated that the frequency of haplotype ADG in the promoter region of ST6GALNAC2 was significantly higher in IgAN patients than that in controls (p=0.0069; odds ratio [OR]=1.36; 95% confidence interval [CI], 1.08-1.72). Furthermore, the ADG haplotype was associated with the deficient degrees of alpha2,6 sialic acid of IgA1 molecules in IgAN patients (r=0.408, p=0.0035). The ADG haplotype conferred significantly reduced promoter activity compared with the most common haplotype GDG in vitro (196.43+/-21.55 vs. 258.41+/-46.25; p=0.002). In the present study, we identified for the first time the ADG haplotype in the ST6GALNAC2 gene as a functional regulatory variant that may contribute to the genetic susceptibility in a subset of patients in whom the desialylation of IgA1 molecules was the main causative pathogenesis of IgAN.     

Binding capacity and pathophysiological effects of IgA1 from patients with IgA nephropathy on human glomerular mesangial cells

IgA deposition in glomerular mesangium and the interaction with mesangial cells may well be the final common pathway to IgA nephropathy (IgAN). Altered hinge-region O-glycosylation of IgA1 from patients with IgAN may predispose to mesangial deposition and activation of the mesangial cell (MC) by IgA1, via a novel IgA1 receptor, and may be a key event in the pathogensis of IgAN. The aim of this study was to investigate the binding capacity and biological effects of IgA1, from both patients with IgAN and healthy controls, on human mesangial cells (HMC). Serum IgA1 was isolated with jacalin affinity chromatography, heated to aggregated form (aIgA1) and labelled with (125)I. Binding capacity of aIgA1 in vitro to cultured primary HMC was evaluated by a radioligand binding assay and the specificity of binding was determined by a competitive inhibition assay. Intracellular calcium release was studied by confocal analysis and phosphorylation of extracellular signal-regulated kinase (ERK) was determined by Western blot analysis. Change of cell cycles was demonstrated by flow cytometry and HMC proliferation was evaluated by direct cell count. Expression of TGF-beta mRNA and production of supernatant fibronectin were tested by RT-PCR and indirect competitive ELISA, respectively. aIgA1 from both the patients with IgAN and normal controls bound to HMC in a dose-dependent, saturable manner, and was saturated at approximately 500 pmoles per 0.5 ml of aIgA1. aIgA1 from patients with IgAN, however, bound to HMC at a higher speed and Scatchard analysis revealed a Kd of (8.89 +/- 2.1) x 10(-8)m versus (4.3 +/- 1.2) x 10(-7)m for aIgA1 from healthy controls (P = 0.026).The binding was specific because it was only inhibited by unlabelled Mono-IgA1 (mIgA1) and not by serum albumin or IgG. aIgA1 from patients with IgAN could induce release of intracellular calcium, phosphorylation of ERK, DNA synthesis, proliferation of HMC, expression of TGF-betamRNA and secretion of fibronectin in HMC in a similar time-dependent manner as aIgA1 from healthy controls, but the effects were much stronger and the durations were much longer (P < 0.05, respectively). We conclude that aIgA1 from patients with IgAN has a higher binding capacity to HMC and stronger biological effects than aIgA1 from healthy controls. This suggests that direct interaction between IgA1 and HMC and subsequential pathophysiological responses may play an important role in the pathogenesis for IgAN.     

Immune response of tonsillar lymphocytes to Haemophilus parainfluenzae in patients with IgA nephropathy

The pathogenesis of IgA nephropathy (IgAN) is unclear. We have previously shown glomerular deposition of Haemophilus parainfluenzae (HPI) antigens and the presence of IgA antibody against HPI antigens in patients with IgAN. We examined the immune response to HPI antigens in tonsillar lymphocytes from patients with IgAN. Lymphocytes isolated from the palatine tonsils of 13 IgAN patients and 16 patients with chronic tonsillitis but without renal disease were used as controls. We examined lymphocyte proliferation and production of IgA antibody against HPI antigens by measuring thymidine uptake and IgA antibody in culture supernatants after lymphocyte incubation with HPI antigens. Patients with IgAN showed a significantly higher stimulation index to HPI antigens (thymidine incorporation in tonsillar lymphocytes with HPI/thymidine incorporation in unstimulated tonsillar lymphocytes) than controls (P < 0.002). Lymphocytes from patients with IgAN also showed a significantly higher level of IgA antibody and IgA1 antibody against HPI antigens in culture supernatants than lymphocytes from controls (P = 0.0002 and P = 0.004, respectively). Our results suggest that HPI antigens stimulate tonsillar T and B lymphocytes in patients with IgAN and that an immune response to HPI antigens may play a role in the pathogenesis of this disease in some cases.     

Clinicopathologic comparisons of IgA nephropathy and IgA vasculitis nephropathy in children: a ten-year single-center experience

Background/aim To investigate the similarities and differences of renal clinical and renal pathology between IgA nephropathy (IgAN) and IgA vasculitis nephritis (IgAVN) in children. Materials and methodsA total of 237 children with IgAN and 190 children with IgAVN were included. The general conditions, clinical characteristics, final diagnosis, clinical and pathological classification of the children were intercepted at the time of admission, and the retrospective comparative analysis was carried out. ResultsThe results showed that the median course of disease in IgAN group was longer than that in IgAVN group (p = 0.02). Patients with IgAN had a significantly higher duration of infection than the patients with IgAVN (p = 0.03). The white blood cell count (WBC), hemoglobin (HGB) in IgAN group were significantly lower than that in IgAVN group (p = 0.02). The serum creatinine in IgAN group was higher than that in IgAVN group (p = 0.02). Patients with IgAN and IgAVN had statistically significant differences in pathological typing between clinical types: hematuria and proteinuria, nephrotic syndrome and chronic nephritis (p = 0.004). ConclusionThe clinical manifestations of IgAN and IgAVN were similar, but the onset of IgAN was hidden and the clinical manifestations were relatively serious. Renal pathology was mainly glomerulosclerosis and renal tubular atrophy. IgAVN was characterized by acute onset and good renal function. Renal pathology was dominated by endothelial hyperplasia and crescent formation. These differences did not support the hypothesis that the two diseases are the same.     

Elution of IgA from kidney tissues exhibiting glomerular IgA deposition and analysis of antibody specificity.

Glomerular IgA deposits were eluted from renal biopsy specimens exhibiting IgA nephropathy (IgAN) by using a combination of citrate buffer and collagenase. Collagenase predigestion of the kidney tissues resulted in increased amounts of IgA eluted by citrate buffer, and the elusion procedure did not attenuate the antigen-binding ability of IgA antibody. When reactivity of the eluted IgA with bacteria components was examined by Western blotting, the most notable reaction was observed for Haemophilus influenzae lysates in the form of a 34 kD-band. The reactivity of IgA eluted from the kidney tissues against the H. influenzae 34 kD antigen was evident in 3 of 5 IgAN cases. However, similar reactivity was also evident in 2 of 6 non-IgAN hepatic diseases exhibiting a glomerular IgA deposition. These findings suggest that antibody specificity of IgA against H. influenzae itself may not be directly associated with glomerular injury, although anti-H. influenzae 34 kD IgA was deposited in the kidney, at least in part, by IgAN. Further investigations into the properties of IgA deposited in the glomerulus are needed. Our improved method for IgA elution from kidney tissues would be useful for analysing the pathogenesis of IgAN.     

IgA nephropathy and alcoholic liver cirrhosis. A prospective necropsy study

The incidence of mesangial IgA nephropathy (mIgAN) was investigated in a series of patients with alcoholic liver cirrhosis (ALC). Biologic parameters classically reported in IgAN were assessed in 98 patients, namely hematuria, proteinuria, and serum IgA. An immunohistologic study of the liver and kidney was performed in 33 patients who died during the study. Renal data were compared with those obtained in a matched necropsic series of controls. This study confirmed a global elevation of serum IgA levels in ALC. A possible hepatic origin of these immunoglobulins was supported by the observation of plasma cells in portal spaces in 68% of the patients. Biologic signs of renal disease consistent with mIgAN were observed in 16% of the patients; IgAN was diagnosed in 18% of patients with ALC and 10% of the controls. These data suggest that the incidence of mIgAN in ALC is not different than in the general population.     

Capsaicin induces high expression of BAFF and aberrantly glycosylated IgA1 of tonsillar mononuclear cells in IgA nephropathy patients

Background

IgA nephropathy (IgAN) is the most common type of primary glomerulonephritis in the world. Hot pepper is the most favorite vegetable for Chinese in Hunan and Sichuan provinces. It can be assumed that capsaicin, the active ingredient of hot pepper, is a possible risk factor in diet in the pathogenesis of IgAN.

Methods

22 subjects, including 11 IgAN patients and 11 non-IgAN patients were enrolled in this study. Tonsillar mononuclear cells were isolated and cultured for 3 days with or without capsaicin.

Results

In the absence and presence of capsaicin, the BAFF expression and IgA1 secretion were higher in IgAN patients than that in non-IgAN patients, meanwhile, the gene expression of C1GALT1 and Cosmc and IgA1 O-glycosylation level were significantly lower. In IgAN group, coincubated with capsaicin, IgA1 and BAFF secretion and BAFF expression by TMCs were significantly higher than that without capsaicin, furthermore, the level of mRNA encoding C1GALT1 and Cosmc and the level of IgA1 O-glycosylation were evidently lower.

Conclusion

Capsaicin may induce IgA1 secretion by activating BAFF expression, and bring to aberrantly IgA1 O-glycosylation by suppressing C1GALT1 and Cosmc expression. Therefore, to limit the consumption of hot pepper would be beneficial to patients with IgA nephropathy.     

Increased and prolonged production of specific polymeric IgA after systemic immunization with tetanus toxoid in IgA nephropathy.

IgA nephropathy (IgAN) is a chronic form of glomerulonephritis which is characterized by the deposition in the glomerular mesangium of polymeric IgA (pIgA), the source of which is unknown. In order to investigate the production of pIgA in IgAN, patients were immunized systemically with tetanus toxoid (TT). Two weeks after immunization patients and controls responded to TT with an IgA response of similar magnitude. HPLC separation of sera showed that patients with IgAN produce significantly more pIgA anti-TT than controls (7.7 versus 2.88 arbitrary units; P less than 0.04). At this time, 33% of serum IgA anti-TT produced by patients with IgAN was polymeric, compared with 21% produced by controls (P less than 0.02). Monomeric IgA (mIgA) anti-TT levels were similar in both groups. Four weeks after immunization the proportion of pIgA anti-TT in controls and patients was significantly reduced from the 2 week level (from 21% to 0%, P less than 0.02 for controls; and from 33% to 8%, P less than 0.001, for patients). Only four out of 12 controls had any detectable pIgA anti-TT at this time compared with nine out of 10 patients with IgAN (P less than 0.05), and IgAN patients produced proportionally more pIgA anti-TT than did controls (median 8%, interquartile ranges (IQR) 4-10% versus 0% IQR 0-3%; P less than 0.01). HPLC analysis under acid conditions did not alter the pattern of pIgA and mIgA anti-TT, suggesting that the high molecular weight IgA fraction was not due to complexes. These data indicate that circulating pIgA results (at least in part) from a systemic response to antigen, which may be exaggerated in IgAN.     

Up-regulation of CX3CR1 on tonsillar CD8-positive cells in patients with IgA nephropathy

Although tonsillectomy are used as therapeutic options to prevent chronic renal failure in IgA nephropathy (IgAN) patients, the relationship between IgAN and tonsils is not fully proved by basic research. Recently, circulating CX3CR1-positive cells were reportedly involved in promoting hematuria in patients with IgAN. In this study, we focused on the expression of CX3CR1 in tonsillar mononuclear cells in IgAN patients. Immunohistological analysis revealed greater distribution of CX3CR1-positive cells in the inter-follicular area of tonsils in IgAN patients than in non-IgAN patients. CX3CR1-positive cells were also found in the affected renal glomerulus of IgAN patients. Flow cytometric analysis revealed the expression of CX3CR1 on tonsillar CD8-positive cells to be significantly higher in IgAN patients. CpG-oligodeoxynucleotides enhanced the expression in IgAN patients. The chemotactic response of tonsillar mononuclear cells to fractalkine was significantly higher in IgAN patients. Expression of CX3CR1 on peripheral blood CD8-positive cells in IgAN patients was significantly higher, and decreased after tonsillectomy, along with the disappearance of hematuria. These results suggest that hyper-immune response to microbial DNA enhanced the expression of CX3CR1 on tonsillar CD8-positive cells in IgAN patients, followed by the migration of the cells to renal lesions via blood circulation, resulting in the development of hematuria.     

Immunopathological features of palatine tonsil characteristic of IgA nephropathy: IgA1 localization in follicular dendritic cells

IgA nephropathy (IgAN) is generally thought to be mediated by the glomerular deposition of circulating immune complexes containing IgA as the major antibody component. Upper respiratory infections and tonsillitis often precede IgAN. and in some cases tonsillectomy is affective for the (treatment of IgAN. Thus, the tonsil seems to be a unique organ causing initial and/or progressive events to generate nephritogenic immune complexes in IgAN. in this study we focused on the analysis of immunopathological features of the palatine tonsil characteristic of IgAN patients by using an immunohistochemical technique. The IgAl subclass was demonstrated in follicular dendritic cells (FDC) of the tonsil of IgAN patients, but not in FDC of non-IgAN controls. On the other hand, IgA2, IgG, IgM and C3 did not show any differences in distribution between the two groups. Moreover, the expression of decay-accelerating factor (DAF), an inhibitor of homologous complement activation, and transforming growth factor-beta I (TGF-/β1). an inducer of antibody-producing ceils to IgA class switching, in FDC and interdigitating dendritic cells of the tonsil, respectively, which was also clarified in this study for the first time, was found to be identically distributed in the two groups. These findings may support the idea that IgA1. possibly in an immune complex form, is trapped by FDC and plays an important role in the persistent activation of particular B cell repertoires responsible for ihe onset and/or progression of IgAN.     

Urinary IgA in IgA nephropathy and Henoch-Schoenlein purpura

To determine the concentrations and molecular forms of urinary IgA in IgA nephropathy and Henoch-Schoenlein purpura, we studied 29 patients with these IgA-associated renal diseases (IgAN). Control groups comprised 10 patients with other diverse renal diseases and 11 healthy volunteers. Urinary IgA and IgG concentrations were higher in IgAN than in either control group and correlated positively with the serum creatinine concentration as well as the urinary protein excretion (P<0.01). However, IgA/IgG ratios did not differ among the three groups. Polymeric IgA (p-IgA) in the urine predominated only in normals; in IgAN and patients with other renal diseases, monomeric IgA (m-IgA) occurred almost exclusively. Serum IgA concentrations were generally normal in IgAN; four patients had concentrations greater than 500 mg/dl. Although the fraction of p-IgA in serum (median, 18%) was increased above normal (5–10%) in 13 of 16 (81%) subjects, neither the concentration of IgA or IgG nor the amount of p-IgA correlated with the serum creatinine concentration. These data suggest that the molecular form and concentration of urinary IgA are not discriminating for IgAN and are independent of these characteristics of serum IgA.     

Serum levels and in vitro production of IgA subclasses in patients with primary IgA nephropathy

Patients with primary IgA nephropathy have deposits of IgA1 in their kidneys, and increased plasma levels of macromolecular IgA1. Total serum IgA concentrations are frequently elevated, but studies on the subclass distribution have been few and conflicting. Several investigators found that production of IgA by peripheral blood lymphocytes in culture is increased. However, the distribution of the IgA subclasses produced has not been studied previously. We studied the serum IgA subclasses in 14 patients with IgA nephropathy, and found a significant (P less than 0.001) increase in IgA1 (3.71 +/- 1.34 mg/ml, mean +/- s.d.) compared with controls (1.77 +/- 1.10 mg/ml). Serum IgA2 was not different in patients and controls. The ratio of serum IgA1 to total IgA was also significantly (P less than 0.001) higher in patients (92.2 +/- 4.9%) than in controls (80.2 +/- 6.6%). Studies of immunoglobulin production by peripheral blood mononuclear cells showed a significant increase in IgA1 synthesis, expressed as a fraction of total IgA synthesis in unstimulated cultures (P less than 0.05) and in PWM stimulated cultures (P less than 0.01). Polymeric IgA and polymeric IgA1 production were not higher in patients than in controls. IgM production in unstimulated cultures was significantly (P less than 0.05) higher in patients than in controls. Together with the observed deposition of exclusively IgA1 in the mesangium, our results indicate that patients with IgA nephropathy preferentially produce antibodies of the IgA1 subclass.