Specific binding of circulating IgA antibodies in patients with IgA nephropathy

Detection of circulating IgA antibodies which are specific in patients with IgA nephropathy is described. Freeze and thawed extracts of pharyngeal cells obtained from patients with IgA nephropathy, other glomerular diseases, and healthy adults were cultured with fibroblasts such as Vero or Hel cells at 37 degrees C for 2 weeks. Serum samples were obtained from these patients and healthy adults. The cultured fibroblasts were fixed on slide glasses, and then incubated with the serum samples from the same or other patients with IgA nephropathy. The cells were stained with FITC-labeled heavy-chain specific anti-human IgA antiserum and then examined with a fluorescent microscope. It was demonstrated that the IgA antibodies in sera obtained from patients with IgA nephropathy or HSP nephritis were bound with the nuclear regions of such fibroblasts. It was suggested that IgA antibodies in sera could be bound with some antigenic substances which were transferred from pharyngeal cells of patients with IgA nephropathy to fibroblasts in vitro.     

Cytopathic effects of antigens in patients with IgA nephropathy

The cytopathic effects of extracts of pharyngeal cells from patients with IgA nephropathy on fibroblasts were determined. Autoradiographical analysis of antigens in the fibroblasts was also described. Freeze and thawed extracts of pharyngeal cells obtained from patients with IgA nephropathy, other glomerular diseases and healthy adults were cultured with fibroblasts such as Vero or Hel cells at 37 degrees C for 1 or 2 weeks. The cytopathic effects of fibroblasts were examined with a light microscope. In addition, the eluate obtained from renal tissues of IgA nephropathy was labeled with iodine-125 by the chloramine-T method. These cultured fibroblasts were incubated with iodine-125-labeled eluate from the same or other patients with IgA nephropathy. The degree of cytopathic effects of extracts of pharyngeal cells from patients with IgA nephropathy on Vero or Hel cells was significantly increased compared with that from patients with other glomerular diseases or healthy adults without glomerular diseases. The cytopathic effects of such fibroblasts were not inhibited by filtration of extracts of pharyngeal cells obtained from patients with IgA nephropathy. It was shown that the antibodies eluted from renal tissues of patients with IgA nephropathy specifically bound with the nuclear regions of such fibroblasts. It was suggested that some antigenic substances might exist in the epithelial cells of the upper respiratory tracts of some patients with IgA nephropathy, and that such antigens were able to be transferred to cultured fibroblasts.     

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

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

Crescentic IgA nephropathy as a manifestation of human immune deficiency virus infection

A 37-year-old Caucasian male homosexual presented with hematuria and rapidly progressive acute renal failure. He was found to have proteinuria and microscopic hematuria as well as RBC casts. Investigations revealed polyclonal gammopathy with five times normal serum IgA levels as well as elevated serum IgG. Renal biopsy showed evidence of crescentic IgA nephropathy with ultrastructural changes of tubuloreticular inclusions described in HIV nephropathy. He was found to be positive for human immunodeficiency viral antibodies. Renal function improved during follow-up after two doses of 1 g each of methylprednisone. In our opinion, this is the first case of HIV-related crescentic IgA nephropathy. HIV testing should be performed more frequently in patients presenting with acute glomerular diseases.     

Predominant synthesis of IgA with lambda light chain in IgA nephropathy

The nature of the light chains in mesangial IgA deposits and serum IgA was studied in patients with IgA nephropathy. Immunofluorescence (IF) studies using murine monoclonal antibodies, rabbit and goat anti-human monospecific antisera were performed in kidney sections from 15 IgA nephritic patients with only IgA isotype detected in the renal biopsy. Lambda light chain IF was demonstrated in all biopsy specimens and kappa light chain IF in 11 renal biopsy specimens. The majority of renal biopsies showed a predominance of lambda light chain IF staining in the mesangial deposits. The concentration of individual immunoglobulins and their light chain fractions, and the kappa/lambda ratio were determined in the serum and the supernate from peripheral blood mononuclear cells culture of 30 IgA nephritic patients and 30 age-matched healthy controls. The IgA nephritic patients had a higher serum concentration of total IgA (P less than 0.001) and a significantly lower IgA kappa/lambda ratio (P less than 0.001) compared with the controls. The kappa/lambda ratio of supernatant IgA from IgA nephritic patients (N = 20) was also significantly lower than that of the normal subjects (N = 14), both in the unstimulated (P less than 0.01) and pokeweed mitogen stimulated, peripheral blood mononuclear-cell culture (P less than 0.05). Our results showed that patients with primary IgA nephropathy displayed a unique immunologic response characterized by a predominance of IgA with lambda light chain in circulation.     

Heparan sulfate proteoglycans are lost in patients with diabetic nephropathy.

The pathogenesis of diabetic nephropathy relative to the changes in the glomerular extracellular matrices was investigated. Renal tissues from 10 diabetic patients were immunostained with antibodies directed against heparan sulfate proteoglycans (HS-PGs), laminin, type IV collagen and fibronectin. Seven patients were nephrotic and had advanced glomerulosclerosis with nodular lesion, while the other 3 had no renal manifestations or minor glomerular tissue alterations. Controls included kidneys removed from patients with renal tumors and specimens obtained by renal biopsy from patients with IgA nephropathy. Relationships among proteinuria, intensity of fluorescence and glomerular changes were studied. In diabetes 3 patients with minor glomerular lesions were found to have no changes in various components of extracellular matrices. A marked reduction in the intensity of staining with anti-HS-PG antibodies was observed in renal specimens from patients with nodular glomerulosclerosis and proteinuria, while a mild decrease in the intensity of fluorescence was observed in tissues stained with antilaminin antibodies. An increase compared to normal control sample findings in type IV collagen and fibronectin was observed in the mesangium of sclerosing glomeruli. No loss of HS-PG was observed in patients with IgA nephropathy. These results indicate that glomerular extracellular matrix HS-PG is lost in association with diabetic nephropathy; this loss results in alteration of the charge-selective properties of glomerular capillaries. This alteration may, in part, be the cause of the proteinuria associated with diabetic nephropathy.     

Staphylococcus aureus cell envelope antigen is a new candidate for the induction of IgA nephropathy

BACKGROUND: IgA nephropathy is the most common form of glomerulonephritis worldwide. We previously reported a novel form of glomerulonephritis with glomerular IgA deposits following methicillin-resistant Staphylococcus aureus (S. aureus) infection. We investigated the role of S. aureus related antigens in the immunopathogenesis of IgA nephropathy by producing several monoclonal antibodies against S. aureus surface antigens and determining the epitopes of deposited antigens in patients with IgA nephropathy. METHODS: Cell membrane proteins were isolated from cultured S. aureus. Mouse monoclonal antibodies against these proteins were generated, and their target epitopes were determined by antibody affinity chromatography and amino acid sequence analysis, and by monoclonal antibody screening of Escherichia coli clones transfected with plasmids from the Lambda S. aureus Genomic Library. Renal biopsy specimens from 116 patients with IgA nephropathy and 122 patients with other forms of renal disease were examined for glomerular antigen depositions by immunofluorescence microscopy. RESULTS:. The major antigen recognized by monoclonal antibodies against S. aureus cell membrane was identified as the S. aureus cell envelope antigen designated 'probable adhesin' (ACCESSION AP003131-77, Protein ID; BAB41819.1). In 68.1% (79/116) of renal biopsy specimens from patients with IgA nephropathy, S. aureus cell envelope antigen was localized in the glomeruli, and the data confirmed that S. aureus cell envelope antigen was co-localized with IgA antibody in the glomeruli. No deposition of this antigen was detected in the glomeruli of patients with non-immune complex deposit forms of glomerulonephritis. CONCLUSION: S. aureus cell envelope antigen is a new candidate for the induction of IgA nephropathy.     

Discriminant analysis of clinical markers before renal biopsy in patients with IgA nephropathy

Discriminant analysis of clinical markers before renal biopsy in patients with IgA nephropathy is described. Sixty eight patients with IgA nephropathy (IgA nephropathy group) and 66 patients with other chronic glomerulonephritis (non-IgA nephropathy group) were examined. The discriminant analysis was applied to separate those two groups by using twenty clinical parameters as well as binding capacity of serum IgA to the glomeruli of renal specimens. Binding of serum IgA of patients to the glomeruli obtained from patients with IgA nephropathy was performed using avidin-biotin immunofluorescence. Among twenty clinical markers, the levels of serum IgA and creatinine, and degree of microhematuria in IgA nephropathy group were significantly higher than those in non-IgA nephropathy group Furthermore, the positive incidence of serum IgA binding of IgA nephropathy group was significantly higher than that of serum IgA binding of non-IgA nephropathy group. The correct classification rate were 79.10% using five clinical markers including serum IgA, microhematuria, serum C4, quantitation of proteinuria and degree of proteinuria. It is indicated that the levels of serum IgA and the binding of serum IgA to the glomeruli were considered to be major markers for clinical diagnosis of patients with IgA nephropathy It was concluded that the discriminant analysis before renal biopsy was useful for diagnosis of IgA nephropathy.     

Apoptotic cells in six patients with IgA nephropathy in repeat biopsies

SUMMARY: Programmed cell death is a selective process of physiological cell deletion and is known as apoptosis. The purpose of the present study was to determine the relationship between the existence of apoptotic cells in glomeruli and the clinical or histopathological findings obtained in repeat renal biopsies of patients with IgA nephropathy. Repeat renal biopsy specimens were obtained from six patients with IgA nephropathy. The nick end labelling method (TUNEL) was used for the detection of apoptotic cells. Clinical laboratory data, i.e. urinary protein excretion, creatinine clearance (Ccr), blood urea nitrogen (BUN) and serum creatinine, (s‐Cr) were obtained from these patients. At the first renal biopsy, apoptotic cells in the glomeruli were observed in three out of six patients using TUNEL. These patients were classified as the severe glomerular damage group. The other three patients without apoptotic cells were in the mild glomerular damage group. Mean levels of urinary protein excretion at the first renal biopsy in the patients with apoptotic cells were slightly higher than those in patients without apoptotic cells. Levels of Ccr in patients with apoptotic cells were lower than those in patients without apoptotic cells. There were no significant differences in the levels of BUN and s‐Cr in patients with or without apoptotic cells. Two patients with apoptotic cells in glomeruli at the first renal biopsy did not show apoptotic cells at the second renal biopsy. These two patients showed improvement not only in clinical laboratory findings but also in histological findings at the second biopsy. Only one patient with apoptotic cells at the first and second biopsies exhibited deterioration at the second biopsy. All three patients without apoptotic cells at the first renal biopsy also showed deterioration of the clinical laboratory and histopathological findings. It is postulated that various factors other than apoptosis might induce progression of renal injuries in such patients. It appears that the clinical laboratory data, i.e. proteinuria, renal function and histopathological findings, might be influenced by apoptosis in patients with IgA nephropathy. It is postulated that apoptosis may induce reduction of excess proliferative glomerular mesangial cells and/or infiltrating cells and tissue repair.     

The number of CD10-positive glomerular epithelial cells reflects renal prognosis in IgA nephropathy patients

BACKGROUND: The glomerular epithelial cells play an important role in glomerular filtration of the kidney. The disruption of these cells contributes to the development of glomerulosclerosis. The present study was performed to elucidate whether loss of the glomerular epithelial cells is associated with renal injury in patients with IgA nephropathy. PATIENTS AND METHODS: Thirty renal biopsy specimens from IgA nephropathy, 12 from minor glomerular abnormalities and 5 from normal controls were observed. The specimens from IgA nephropathy were divided into 2 groups: Group IgA-1, including 11 patients who had received a follow-up renal biopsy because of deterioration of renal function, and Group IgA-2, consisting of the remaining 19 patients without follow-up biopsy. Immunohistochemistry was performed using a monoclonal antibody against CD10 antigen that appears on mature epithelial cells of glomeruli. RESULTS: The average number of CD10-positive glomerular epithelial cells (GECs) was significantly lower in IgA nephropathy than in either minor glomerular abnormalities or the normal controls. In IgA nephropathy, there were significant correlations of the GECs with renal functions. The GECs were reduced along with the progression of histopathological damage. In group IgA-1, the GECs were significantly reduced at the second biopsy compared with the first biopsy, and significantly fewer in group IgA-1 than in group IgA-2 at the first biopsy. The GECs showed a significant correlation with renal prognosis during the follow-up period. CONCLUSIONS: The reduction of GECs was associated with renal dysfunction, histopathological damage and renal prognosis. The GECs may be a useful predictor of renal prognosis in IgA nephropathy.     

Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy

BACKGROUND: The IgA1 molecule, which is predominantly deposited in glomeruli in IgA nephropathy (IgAN), is a unique serum glycoprotein because it has O-glycan side chains in its hinge region. Our study was conducted to investigate the O-glycan structure in the glomerular IgA1 in IgAN. METHODS: The IgA1 was separated from 290 renal biopsy specimens of 278 IgAN patients and from four serum IgA1 samples (IgAN, 2; control, 2). The variety of O-glycan glycoform was determined by estimating the precise molecular weights of the IgA1 hinge glycopeptides using matrix-assisted laser desorption ionization time of flight mass spectrometry. RESULTS: The peak distribution of IgA1 hinge glycopeptides clearly shifted to lesser molecular weights in both glomerular and serum IgA1 in IgAN compared with the serum IgA1 of controls. In the five major peaks of IgA1 hinge glycopeptides in each sample, the numbers of carbohydrates composing O-glycans (GalNAc, Gal, and NANA) in the deposited and serum IgA1 in IgAN patients were significantly fewer than those in the serum IgA1 in the control groups. CONCLUSION: The O-glycan side chains in the hinge of the glomerular IgA1 were highly underglycosylated in IgAN. These results indicate that the decreased sialylation and galactosylation of the IgA1 hinge glycopeptides play a crucial role in its glomerular deposition in IgAN.     

Occurrence of anti-C1q antibodies in IgA nephropathy

Background: The pathogenic mechanisms and the antigens involved in the establishment and progress of IgA nephropathy are unknown. As antibodies against C1q have been reported to correlate with SLE nephritis, we analysed the occurrence of these antibodies in IgA nephropathy in order to investigate the possibility of pathogenetic similarities in these renal disorders. Methods: The occurrence of IgA- and IgG anti-C1q antibodies (anti-C1q) were determined by ELISA in patients with IgA nephropathy (n=36) and SLE nephritis (n=37), diseases both known to be associated with circulating immune complexes. Levels of these antibodies were also determined in two other glomerular diseases, i.e. idiopathic membranous glomerulo-nephritis (n=7) and minimal change disease (n=2), in which circulating immune complexes are usually not present, and in 40 healthy controls. Results: IgA anti-C1q was observed in increased titres in 11/36 of the patients with IgA nephropathy, in 2/37 of the patients with SLE nephritis (both with proliferative disease) and in 1/9 of the patients with membranous and minimal change disease (P<0.001). Increased titres of IgG anti-C1q were observed in 1/36 of the patients with IgA nephropathy, in 17/37 of the patients with SLE nephritis and in 0/9 of the patients with membranous and minimal change disease (P<0.001). There were no correlations between the levels of anti-C1q antibodies and clinical parameters such as degree of proteinuria, haematuria, or renal function. Nor was there any correlation to the concentration of C3a and the terminal complement complex (TCC) in patients with IgA nephropathy. Conclusions: The occurrence of anti-C1q antibodies in both IgA nephropathy and SLE nephritis, albeit of different predominating isotypes, indicates the possibility of a similar pathogenic mechanism involved in these renal disorders. The occurrence of IgA anti-C1q antibodies in patients with IgA nephropathy has to our knowledge not previously been reported.     

Repeat renal biopsy in children with IgA nephropathy

Serial renal biopsy findings in 61 children with IgA nephropathy were correlated with their clinical course. At the time of the second biopsy, 23 patients showed clinical remission defined as complete disappearance of proteinuria and hematuria with normal renal function while 38 had persistent urinary abnormalities with normal renal function at the second biopsy. There were no differences between the two groups with regard to initial clinical findings and pathologic findings of the initial renal biopsy. The second biopsy of patients with clinical remission showed improvement of the glomerular changes on light microscopy, disappearance or diminution of IgA deposits in the mesangium and decrease of electron-dense deposits, whereas the second biopsy of patients with persistent urinary abnormalities showed progression of glomerular changes on light microscopy, persistence of mesangial IgA deposits and persistence of electron-dense deposits. Our study results show the importance of repeat renal biopsy in children with IgA nephropathy with persistent urinary abnormalities, as a progression of glomerular changes is common in these patients. These observations suggest that the deposition of IgA in the mesangium may be responsible for the glomerular damage in children with IgA nephropathy.     

血清低半乳糖化IgA1测定对鉴别IgA肾病的临床价值

目的 确定血清低半乳糖化IgA1对鉴别诊断IgA肾病的临床价值。 方法 以原发性肾小球疾病患者91例为研究对象，接受肾活检并留取血清；以健康体检者20例血清作为对照。血清标本先用装有耦联蚕豆凝集素的微球进行微量离心柱法分离并洗脱，获得低半乳糖化IgA1。再以凝集素HAA（Helix aspersa）用ELISA法定量检测异常糖基化IgA1（HAA-IgA1）。分析血清低半乳糖IgA1升高在鉴别诊断IgA肾病方面的临床价值。 结果 48例IgA肾病患者HAA-IgA1水平[（83.7±41.0） U]高于健康对照组[（52.6±22.9） U]及43例其他原发性肾小球疾病患者组[（49.2±27.3） U]（均P < 0.01）。而该43例中，非IgA系膜增殖性肾炎患者22例（51%）的HAA-IgA1水平[（47.6±21.5） U]亦显著低于IgA肾病患者。以肾穿刺病理诊断为金标准，所绘制ROC曲线面积为0.797，面积的标准误为0.047（P < 0.01）；鉴别诊断IgA肾病的灵敏度为72.9%，特异度为72.1%，准确度为72.5%。 结论 应用微量离心柱法联合ELISA法检测IgA肾病患者血清低半乳糖IgA1对于鉴别诊断IgA肾病具有一定临床价值。     

Circulating and mesangial secretory component-binding IgA-1 in primary IgA nephropathy

In a prospective study of 38 patients who presented with hematuria of renal origin, 15 patients were found to have primary IgA nephropathy and 23 had other renal disorders. Sera and renal biopsy specimens of these patients were studied for the presence of macromolecular IgA1 and IgA2 using monoclonal antibodies, and the presence of J-chain as demonstrated either by immunofluorescence or its capacity to bind free secretory component. Circulating macromolecular IgA was found exclusively in the sera of patients (80%) with primary IgA nephropathy. In these sera the polymer/monomer ratio for IgA1 (0.64 +/- 0.13) was significantly higher than for normal human serum (0.39 +/- 0.01) (P less than 0.001), while no differences were found for IgA2. The polymeric IgA1 was isolated from serum by gel chromatography and was shown to have the capacity to bind free secretory component. Direct two-color immunofluorescence studies revealed the presence of only IgA1 in the mesangial deposits and also its capacity to bind free secretory component. We conclude (1) that demonstration of circulating macromolecular IgA in patients with renal hematuria is of diagnostic value and (2) that antigenetic similarities between the circulating and the mesangial macromolecular IgA suggest that dimeric IgA1 is deposited in the mesangium of patients with primary IgA nephropathy.     

Increased urinary excretion of macrophage-colony-stimulating factor (M-CSF) in patients with IgA nephropathy: tonsil stimulation enhances urinary M-CSF excretion

Upper respiratory tract infection including chronic tonsillitis is considered to be involved in the onset and/or the progression of IgA nephropathy. It is well known that deterioration of urinary findings occurs after episodes of upper respiratory tract infection in patients with IgA nephropathy. We previously showed that the expression of macrophage-colony-stimulating factor (M-CSF) is increased in the glomeruli of patients with IgA nephropathy and correlated with glomerular mesangial proliferation, suggesting that M-CSF plays an important role in the progression of IgA nephropathy. In the present study, we measured the serum and urinary concentrations of M-CSF in patients with IgA nephropathy associated with chronic tonsillitis. Furthermore, we evaluated the effects of the local provocation test of tonsils (mechanical tonsil stimulation) on the serum and urinary concentrations of M-CSF in the following three groups: (1) IgA nephropathy with severe mesangial proliferation, (2) IgA nephropathy with mild mesangial proliferation, and (3) patients with chronic tonsillitis without renal disease. The serum and urinary levels of M-CSF in the groups with severe and mild IgA nephropathy were significantly higher than those in the chronic tonsillitis group. The urinary M-CSF level but not the serum M-CSF level was positively correlated with the degrees of mesangial proliferation and glomerular M-CSF expression in the renal biopsy specimens. The urinary M-CSF concentration was significantly increased after tonsillitis stimulation in both mild and severe IgA nephropathy groups. Enhanced urinary excretion of M-CSF prolonged for 7 days after tonsil stimulation in the severe IgA nephropathy group; in contrast, the urinay M-CSF level was increased for only 2 days after tonsil stimulation in the mild IgA nephropathy group. The urinary M-CSF level was not changed in the chronic tonsillitis group after tonsil stimulation. The serum concentrations of M-CSF were not changed after tonsil stimulation in these three groups. Our present results suggest that tonsil stimulation contributes to the progression of IgA nephropathy via enhancement of glomerular production of M-CSF. The urinary excretion of M-CSF may be a useful predictor to evaluate the relevance of chronic tonsillitis to the disease and the indication of tonsillectomy in patients with IgA nephropathy.     

Long-term evolution of renal histology in slowly progressive patients with IgA nephropathy

Recent clinical trials indicate that non-immunological mechanisms (e.g., glomerular hypertension or hypertrophy) may play a crucial role in the progression of patients with IgA nephropathy. Since the long-term renal histological changes in an individual patient with IgA nephropathy are not well elucidated, we assessed the serial renal biopsy specimens from nine patients with IgA nephropathy (five males, four females) where serial biopsies were performed in an interval of more than 10 years (mean 12.8; range 10–20). Histological parameters (i.e. percentage of global sclerosis (GS), tubulo-interstitial lesion (TI), patients (Pt) with cellular crescent (CC) or arteriolosclerosis (AS), mean glomerular area (MGA) and number of glomeruli per renal cortical area (glomerular density, GD)), were compared between the both specimens ( Table 1 ).  

     

Antimouse laminin antibodies in IgA nephropathy and various glomerular diseases.

IgG, IgA and IgM class antibodies to mouse laminin and human fibronectin in sera from patients with various glomerular diseases (50 cases of IgA nephropathy, 5 cases of minimal-change nephrotic syndrome; 6 cases of membranous nephropathy, 5 cases of systemic lupus erythematosus, 2 cases of Henoch-Sch?nlein purpura, 3 cases of poststreptococcal nephritis and 4 cases of preeclampsia) and from 30 normal controls were tested using a solid-phase enzyme-linked immunosorbent assay method. IgA antimouse laminin antibody titers in sera from IgA nephropathy patients were significantly higher (p less than 0.05) than in controls. There were no statistical differences in IgA antimouse laminin antibody titers between patients with other glomerular diseases and normal controls. IgM antimouse laminin antibody was significantly raised (p less than 0.01) in sera from patients with preeclampsia. The reaction of mouse laminin with the IgA nephropathy and preeclampsia sera on each of the IgA and IgM assay systems was inhibited by the antigen at up to 5 micrograms/ml. However, it was not inhibited by anti-C3d, anti-C1q, anti-J chain and antisecretory component sera or saccharides. The reaction of mouse laminin with an exceptionally high-titer IgA antimouse laminin antibody serum from a normal control on the IgA assay system was clearly inhibited by 1 mM of melibiose, which contains alpha-galactosyl residues. The same concentration of melibiose, however, did not inhibit the reaction of mouse laminin with IgA nephropathy sera on the same assay system. Treatment of mouse laminin with alpha-galactosidase did not alter any binding from IgA nephropathy sera but binding was lost from an exceptionally high-titer normal control serum. There were no correlations between serum IgA level and IgA antimouse laminin antibody titer in sera from IgA nephropathy patients. Immunoblot techniques revealed the presence of antibody in sera from IgA nephropathy patients reacting with both subunits A and B of laminin, somewhat stronger with laminin A. None of the sera tested contained antifibronectin antibodies. These results indicate that the IgA antimouse laminin antibody is a specific antibody in IgA nephropathy and might play a role in the pathogenesis of the nephritis since mouse laminin and human mesangial laminin present a common epitope.     

Macroscopic hematuria and proteinuria preceding renal IgA deposition in patients with IgA nephropathy

Although the clinical onset of IgA nephropathy is frequently impossible to define, macroscopic hematuria apparently heralds the onset of the disease in some patients. We describe the clinical course and renal histologic findings of four adults with IgA nephropathy who were diagnosed by the characteristic immunohistologic features in a second renal biopsy specimen. IgA was not detected in the initial renal biopsy specimens obtained 9 months to 4 years earlier. The first renal biopsy had been performed to evaluate macroscopic hematuria (recurrent in three patients), accompanied by pathologic proteinuria in two patients. Our observations suggest that the pathognomonic immunohistologic findings of IgA nephropathy may follow the clinical onset and raise questions about the presumed pathogenetic role of IgA in the early stages of this disease.     

Targeted downregulation of extracellular nephrin in human IgA nephropathy

BACKGROUND: The identification of nephrin and CD2AP, podocyte proteins which modulate the properties of glomerular barrier selectivity, has made it possible to unravel the mechanisms undergoing foot process effacement and proteinuria. Here we explored the role of nephrin and CD2AP together with the integrity of the slit diaphragm in the pathogenesis of proteinuria in patients with acquired glomerular diseases. METHODS: Nephrin mRNA and protein expression were systematically evaluated in 28 renal biopsy samples from adult patients with primary glomerular disease and proteinuria by in situ hybridization and immunohistochemistry using antibodies directed against extra- and intracellular nephrin and compared with biopsy samples from normal controls. CD2AP protein expression by immunohistochemistry was also assessed. Morphometrical analysis of the filtration slit was performed by transmission electron microscopy. RESULTS: Nephrin mRNA and expression of the extracellular nephrin were markedly reduced in IgA nephropathy. No changes were found in patients with minimal change nephrosis and focal segmental glomerulosclerosis. The staining of intracellular nephrin and CD2AP did not change among patients. A comparable frequency of the filtration slits was observed in all patient groups, except in minimal change disease patients, due to extensive foot process effacement. The percentage of slit diaphragms with a filamentous image was markedly reduced in IgA nephropathy, but was comparable to controls in minimal change disease. Slit pore width showed a tendency to decrease both in patients with minimal change disease and IgA nephropathy. CONCLUSIONS: These results indicate that the ultrastructure of the filtration slit diaphragm is altered in patients with IgA nephropathy as a consequence of targeted downregulation of extracellular nephrin. Further studies are needed to evaluate the pathophysiological meaning of nephrin abnormality in IgA nephropathy and how these changes can be modulated by antiproteinuric therapy.