A quantitative study of glomerular basement membrane changes in IgA nephropathy

A closer look: ultrastructural evaluation of high-risk progression IgA nephropathy

This retrospective, cross-sectional study sought to examine the ultrastructural characteristics of glomerular lesions using Transmission Electron Microscopy (TEM) in IgA nephropathy (IgAN) and their relationship with the high risk of progression phenotype defined by KDIGO guideline as proteinuria ≥1 g/24 hours despite 3 months of optimized supportive care. We analyzed 81 IgAN patients (median age 41 years, 67% male, eGFR 43.8 mL/min, proteinuria 1.04 g/day); 42 (52%) of them had high risk of progression. There were no differences in terms of age, sex, comorbidities, eGFR, and hematuria between the two groups. High-risk patients more often had segmental glomerulosclerosis (29% vs 8%, p 0.01) in optical microscopy, while in TEM had more frequent podocyte hypertrophy (62% vs 26%, p 0.001) and podocyte foot process detachment from the glomerular basement membrane (19% vs 8%, p 0.05), more often thicker (19% vs 5%, p 0.05) and duplicated (26% vs 10%, p 0.05) glomerular basement membrane, and the presence of subendothelial and subepithelial deposits (31% vs 13%, p 0.05). However, in multivariate binary logistic regression analysis, only podocyte hypertrophy (OR 3.14; 95%CI 1.12, 8.79) was an independent risk factor for high-risk progression in IgAN. These findings highlight the importance of podocytopathy in IgAN progression.

Prognostic role of glomerular electron microscopy lesions in IgA nephropathy: "the devil is in the details"

INTRODUCTION

Transmission electron microscopy enables examination of ultrastructural glomerular changes; while this tool has already been applied in IgA nephropathy (IgAN), limited information exists on the prognostic value in this disease. We aimed to systematically investigate ultrastructural lesions and assess their role in predicting the evolution of IgA nephropathy to end-stage kidney disease.

METHODS

A single-center retrospective study was performed on 107 consecutive IgAN patients (median age 42 years, 67% male, estimated glomerular filtration rate 46 mL/min, proteinuria 1.0 g/g) between 2010 and 2015, who were followed-up until end-stage kidney disease, death, or end of study (January 2021). A pathologist evaluated the Mesangial hypercellularity (M), Endocapillary hypercellularity (E), Segmental glomerulosclerosis (S), and Tubular atrophy/interstitial fibrosis-Crescents (C) (MEST-C) score and transmission electron microscopy lesions according to a comprehensive protocol that encompassed all glomerular structures.

RESULTS

Patients were followed up for a median of 7.1 years; 32 (43%) reached end-stage kidney disease. Patients who reached kidney failure had higher comorbidity score, more frequent arterial hypertension, lower estimated glomerular filtration rate, and higher MEST-C score. In terms of transmission electron microscopy lesions, patients who progressed to end-stage kidney disease had more frequent podocyte activation, effacement, and presence of microvilli; more frequent signs of endothelial cell activation and fenestration; higher mesangial cell proliferation. In the univariate Cox proportional hazard regression, higher MEST-C score and lesions detected by transmission electron microscopy in podocytes, endothelial cells, and mesangial cell proliferation were associated with shorter kidney survival time. In the multivariate Cox proportional hazard regression, only higher MEST-C score, presence of podocytes with microvilli, and mesangial cell proliferation were associated with end-stage kidney disease.

CONCLUSION

This study shows that, besides the MEST-C score, the presence of podocytes with microvilli and mesangial cell proliferation are associated with poor kidney survival in IgAN patients, highlighting the prognostic value of lesions detected by transmission electron microscopy.

Clinical and immunological characteristics of patients with combined anti-glomerular basement membrane disease and IgA nephropathy

Background

The combination of anti-glomerular basement membrane (GBM) disease and immunoglobulin A nephropathy (IgAN) has been well documented in sporadic cases, but lacks overall assessment in large collections. Herein, we investigated the clinical and immunological characteristics and outcome of this entity.

Methods

Seventy-five consecutive patients with biopsy-proven anti-GBM disease from March 2012 to March 2020 were screened. Among them, patients with concurrent IgAN were identified and enrolled. The control group included biopsied classical anti-GBM patients during the same period, excluding patients with IgAN, other glomerular diseases or tumors, or patients with unavailable blood samples and missing data. Serum IgG and IgA autoantibodies against GBM were detected by enzyme-linked immunosorbent assay, as were circulating IgG subclasses against GBM.

Results

Fifteen patients with combined anti-GBM disease and IgAN were identified, accounting for 20% (15/75) of all patients. Among them, nine were male and six were female, with an average (± standard deviation) age of 46.7 ± 17.3 years. Thirty patients with classical anti-GBM disease were enrolled as controls, with 10 males and 20 females at an average age of 45.4 ± 15.3 years. Patients with combined anti-GBM disease and IgAN had restricted kidney involvement without pulmonary hemorrhage. Compared with classical patients, anti-GBM patients with IgAN presented with significantly lower levels of serum creatinine on diagnosis (6.2 ± 2.9 vs 9.5 ± 5.4 mg/dL, P = .03) and less occurrence of oliguria/anuria (20%, 3/15 vs 57%, 17/30, P = .02), but more urine protein excretion [2.37 (1.48, 5.63) vs 1.11 (0.63, 3.90) g/24 h, P = .01]. They showed better kidney outcome during follow-up (ESKD: 47%, 7/15 vs 80%, 24/30, P = .03). The autoantigen and epitope spectrum were comparable between the two groups, but the prevalence of circulating anti-α3(IV)NC1 IgG1 (67% vs 97%, P = .01) and IgG3 (67% vs 97%, P = .01) were lower in patients with IgAN.

Conclusions

Concurrent IgAN was not rare in anti-GBM disease. Patients showed milder kidney lesions and better recovery after immunosuppressive therapies. This might be partly explained by lower prevalence of anti-GBM IgG1 and IgG3 in these patients.

Utility of glomerular Gd-IgA1 staining for indistinguishable cases of IgA nephropathy or Alport syndrome

BACKGROUND

Pathological findings in Alport syndrome frequently show mesangial proliferation and sometimes incidental IgA deposition, in addition to unique glomerular basement membrane (GBM) changes including thin basement membrane and/or lamellation. However, similar GBM abnormalities are also often observed in IgA nephropathy. Both diseases are also known to show hematuria, proteinuria, and sometimes macrohematuria when associated with viral infection. Therefore, it can be difficult to make a differential diagnosis, even based on clinical and pathological findings. Some recent articles demonstrated that galactose-deficient IgA1 (Gd-IgA1)-specific monoclonal antibody (KM55) could potentially enable incidental IgA deposition to be distinguished from IgA nephropathy.

METHODS

We performed comprehensive gene screening and glomerular Gd-IgA1 and type IV collagen α5 chain immunostaining for five cases with both IgA deposition and GBM changes to confirm that Gd-IgA1 can help to distinguish these two diseases.

RESULTS

Four of the cases were genetically diagnosed with Alport syndrome (Cases 1-4) and one was IgA nephropathy with massive GBM changes, which had a negative gene test result (Case 5). In Cases 1-4, glomerular Gd-IgA1 deposition was not detected, although there was positivity for IgA in the mesangial area. In Case 5, glomerular Gd-IgA1 deposition was observed.

CONCLUSION

Gd-IgA1 expression analysis could clearly differentiate these two disorders. This approach can be applied to identify these two diseases showing identical clinical and pathological findings.

Glomerular basement membrane injuries in IgA nephropathy evaluated by double immunostaining for α5(IV) and α2(IV) chains of type IV collagen and low-vacuum scanning electron microscopy

BACKGROUND

The glomerulus contains well-developed capillaries, which are at risk of injury due to high hydrostatic pressure, hyperfiltration, hypertension and inflammation. However, the pathological alterations of the injured glomerular basement membrane (GBM), the main component of the glomerular filtration barrier, are still uncertain in cases of glomerulonephritis.

METHODS

We examined the alterations of the GBM in 50 renal biopsy cases with IgA nephropathy (31.8 ± 17.6 years old) using double immunostaining for the α2(IV) and α5(IV) chains of type IV collagen, and examining the ultrastructural alterations by transmission electron microscopy (TEM) and low-vacuum scanning electron microscopy (LV-SEM).

RESULTS

The GBM of IgA nephropathy cases showed various morphological and qualitative alterations. In the TEM findings, thinning, gaps, rupture, thickening with a lamellar and reticular structure and double contours were detected in the GBM. Double immunostaining for α5(IV) and α2(IV) showed thickening of the GBM with reduced α5(IV) and increased α2(IV), or mosaic images of α5(IV) and α2(IV), and holes, fractures, spiny projections and rupture of α5(IV) in the GBM. In addition, LV-SEM showed an etched image and multiple holes in a widening and wavy GBM. These findings might be associated with the development of a brittle GBM in IgA nephropathy.

CONCLUSION

Glomerular basement membrane alterations were frequently noted in IgA nephropathy, and were easily evaluated by double immunostaining for α2(IV) and α5(IV) of type IV collagen and LV-SEM. The application of these analyses to human renal biopsy specimens may enhance our understanding of the alterations of the GBM that occur in human glomerular diseases.

CD34 expression as a novel marker of transformed mesangial cells in biopsied glomerular diseases

CD34 is a marker of haematopoietic progenitor cells, stromal precursors, vascular endothelial cells, and a variety of stromal tumour cells. This immunohistochemical study examined the CD34 expression of glomerular mesangial cells in normal and diseased glomeruli and compared it with the staining patterns of alpha-smooth muscle actin (ASMA), as a transformed mesangial cell marker, and CD31, as an endothelial cell marker. In addition, the CD34 and ASMA expression of mesangial cells in various glomerulonephritis and the relationship of the immunostaining intensity to the severity of IgA nephropathy were semiquantitatively evaluated. In normal glomeruli, all cell types were negative for CD34, but in glomeruli in mesangial proliferative glomerulonephritis, CD34 was expressed exclusively in mesangial cells, corresponding to ASMA expression. The dendritic and scattered staining pattern, the mesangial location of positive signals, and the enhanced expression were clearly different from CD31 expression in diseased glomeruli. In comparison with normal controls, the grade of immunostaining for CD34 (CD34 INDEX) in mesangial proliferative glomerular diseases was higher than that of ASMA (ASMA INDEX). With the severity of glomerulonephritis, the CD34 INDEX gradually increased. These studies indicate that CD34 is a useful marker of mesangial transformation and that immunohistochemical examination with the anti-CD34 antibody is useful for the diagnosis and stage determination of glomerular diseases.

Glomerular membranopathy in children with IgA nephropathy and Henoch Schönlein purpura

We evaluated renal biopsies from 34 children with IgA nephropathy or Henoch Schönlein purpura to further characterize the ultrastructural features of the glomerular membranopathy that occurs in these disorders. Focal glomerular basement membrane damage was identified in 29 children and was severe in 4 of the children. Alterations included focal and segmental attenuation, splitting, duplications, and spike-like subepithelial protrusions of the lamina densa, along with saccular glomerular microaneurysms arising at the paramesangium. Those cases with extensive glomerular basement membrane lesions had either moderate or severe glomerular alterations apparent by light microscopy. Over half of the cases with glomerular membranopathy had immunohistological or ultrastructural evidence of focal peripheral glomerular capillary wall immune deposits and electron-dense deposits occurred at sites of glomerular basement membrane splitting. Despite the focal attenuation of the glomerular basement membrane, we did not identify any biopsy with findings of thin basement membrane disease. The glomerular basement membrane ultrastructural findings we describe are characteristic of IgA nephropathy and Henoch Schönlein purpura, are common in children with these disorders, and are similar to the ultrastructural alterations of the basement membrane that occur in other glomerulonephritides. These basement membrane injuries may be inflammatory cell or immune mediated but their pathogenesis requires further study.

Glomerular basement membrane thickness in primary diffuse IgA nephropathy: ultrastructural morphometric analysis

Sixteen renal biopsy specimens from adult patients with IgA nephropathy (IgAN) for whom both light and electron microscopy as well as immunofluorescence microscopy and full clinical data were available were examined quantitatively and compared with six cases of normal controls. The electron micrographs of the glomeruli were scanned in a Primax flatbed A4 scanner and then morphometric investigations were performed by means of a computer image analysis system to evaluate glomerular basement membrane (GBM) thickness and to study whether this parameter could correlate with the degree of the haematuria, which is thought to be a main renal symptom in this glomerulopathy. The study revealed that the mean value of the GBM thickness was in IgAN patients significantly lower in comparison with normal controls (268.6 nm versus 338.8 nm). The authors also noted the tendency to negative correlation between GBM thinning and haematuria, although this relationship was not significant. It is suggested that deposits located in the vicinity of the capillary loops may play a role in this process.

Thin-membrane nephropathy--a common cause of glomerular haematuria

Thin-membrane nephropathy recently has been described as a cause of glomerular haematuria. The prognosis of the condition is unclear but it generally is considered to be benign. In a series of 92 patients with glomerular haematuria, thin-membrane nephropathy was found to be a common cause, occurring in 26 (28%) patients. Sixteen patients were women. The mean age was 42 years. Four patients had a family history of renal disease or haematuria and no patient was deaf. Haematuria had been present from six days to 30 years. Loin pain occurred in 31% of patients. Hypertension was not a feature and mild renal impairment was present in one case only, while a further three cases showed proteinuria at a level of greater than 500 mg of protein per day. Glomerular basement membranes in patients with thin-membrane nephropathy gave a mean (+/- standard deviation) width of 319 + 37 nm which was significantly (P less than 0.002) less than the control value of 394 +/- 61 nm. On the basis of clinical features and serological parameters, thin-membrane nephropathy could not be separated from other renal causes of haematuria but required careful electronmicroscopic examination of renal biopsy material to establish the diagnosis. Limited follow-up has confirmed the good prognosis of the condition.

A histopathological study on the prognosis of childhood IgA nephropathy and glomerular basement membrane lesions

Seventy-three patients with IgA nephropathy (IgAGN), under the age of 15 years at the time of the discovery of the disease, were investigated with respect to glomerular basement membrane (GBM) lesions. Irregular attenuation or widening of GBM, especially on the epithelial side, was observed in 28 cases (38%). These two changes are referred to as lysis of GBM and were considered to be the primary and specific changes among the GBM lesions in IgAGN. GBM thickening with layering of lamina densa was found in 37 of 73 cases (51%), but this change has been observed in other types of glomerular diseases. GBM lesions similar to those seen in IgAGN were also observed in Henoch-Schönlein purpura nephritis (HSPN) and poststreptococcal acute glomerulonephritis (PSAGN). Lysis of GBM was observed only in IgAGN, HSPN and PSAGN. Subepithelial and intramembranous deposits appeared to have an important role in the development of these GBM lesions. The presence of GBM lesions was correlated with a high incidence of cellular crescents but not with other clinical or light microscopic findings. The presence of these GBM lesions in IgAGN does not have a significant effect on the prognosis, at least in childhood. The affected GBM seemed to recover without leaving any significant residual damage in most cases. In the long-term prognosis of the disease non-immunological factors, such as ageing or hypertension, seem to be important.