AJKD Atlas of Renal Pathology: IgA Nephropathy

Systemic vasculitis involving the kidney: the nephropathologist's point of view

Kidneys are often targets of systemic vasculitis (SVs), being affected in many different forms and representing a possible sentinel of an underlying multi-organ condition. Renal biopsy still remains the gold standard for the identification, characterization and classification of these diseases, solving complex differential diagnosis thanks to the combined application of light microscopy (LM), immunofluorescence (IF) and electron microscopy (EM). Due to the progressively increasing complexity of renal vasculitis classification systems (e.g. pauci-immune vs immune complex related forms), a clinico-pathological approach is mandatory and adequate technical and interpretative expertise in nephropathology is required to ensure the best standard of care for our patients. In this complex background, the present review aims at summarising the current knowledge and challenges in the world of renal vasculitis, unveiling the potential role of the introduction of digital pathology in this setting, from the creation of hub-spoke networks to the future application of artificial intelligence (AI) tools to aid in the diagnostic and scoring/classification process.

Improvements in digital pathology equipment for renal biopsies: updating the standard model

INTRODUCTION

Digital pathology can improve the technical and interpretative workflows in nephropathology by creating hub-spoke networks and virtuous collaboration projects among centers in different geographical regions. New high-resolution fast-scanning instruments combined with currently existing equipment were tested in a nephropathology hub to evaluate possible upgrading in the routine processing phases.

METHODS

The scanning performance of two different instruments (Aperio vs hybrid MIDI II) was evaluated and a comparative quality control check was performed on obtained whole slide images.

RESULTS

Both with default and custom settings for light microscopy, MIDI II proved to be faster, with only slightly more time required to prepare the scan and larger final file size as compared to Aperio (p < 0.001). No differences were noted in the number of out-of-focus slides per case (p = 0.75). Regarding immunofluorescence, the new scanner required longer preparation time (p = 0.001) with comparable scanning times and final file size (p = 0.169 and p = 0.177, respectively). Quality control showed differences in 3 quality features related to white background and blurriness (p < 0.001). No major discordances in the final diagnosis were recorded after comparing the report obtained with slides scanned using the two instruments, with only one case (4%) showing minor disagreement.

CONCLUSION

The present report describes the experience of a hub nephropathology center adopting next generation digital pathology tools for the routine assessment of renal biopsies, highlighting the need for a complementary approach towards a philosophy of interoperability.

Drusen and Other Retinal Findings in People With IgA Glomerulonephritis

PURPOSE

Retinal drusen have been described in people with IgA nephropathy. We examined the frequency of drusen in IgA nephropathy and compared their location and composition with those for drusen in age-related macular degeneration.

DESIGN

Immunohistological case series of eyes of patients with IgA nephropathy, and a comparison eye with age-related macular degeneration.

METHODS

Donor eyes from 4 individuals (3 male, 1 female, aged 40-80 years) with biopsy-proven IgA nephropathy and kidney failure were examined for the presence of drusen, and location and composition using antibodies for vitronectin, IgA, IgM, IgG, C3, and C1q. Results were compared with those for drusen in macular degeneration without IgA nephropathy.

RESULTS

All 4 donors had sparse, subretinal pigment epithelium drusen of 55-65 mm diameter that stained for vitronectin but not for IgA or complement. All donors had retinal capillaries and choriocapillaris staining for IgA. The youngest donor (female, 40) had rare deposits in the outer nuclear layer that stained for IgA, but not for vitronectin. The oldest donor (male, 82) had large cystlike spaces in the inner nuclear and plexiform layers, and smaller cysts in the outer nuclear layer, with no staining for IgA or complement.

CONCLUSIONS

Retinal drusen are uncommon in IgA nephropathy, even with kidney failure. Drusen in IgA nephropathy resemble drusen found in age-related macular degeneration. IgA-staining deposits in the outer nuclear layer were likely due to systemic deposition of IgA and complement activation. The nature of cystic spaces is unknown. Further analysis of the retinas of people with glomerulonephritis is recommended.

Present and Future of IgA Nephropathy and Membranous Nephropathy Immune Monitoring: Insights from Molecular Studies

IgA Nephropathy (IgAN) and Membranous Nephropathy (MN) are primary immune-mediated glomerular diseases with highly variable prognosis. Current guidelines recommend that greater immunologic activity and worse prognosis should guide towards the best treatment in an individualized approach. Nevertheless, proteinuria and glomerular filtration rate, the current gold standards for prognosis assessment and treatment guidance in primary glomerular diseases, may be altered with chronic damage and nephron scarring, conditions that are not related to immune activity. In recent years, thanks to the development of new molecular technologies, among them genome-wide genotyping, RNA sequencing techniques, and mass spectrometry, we have witnessed an outstanding improvement in understanding the pathogenesis of IgAN and MN. In addition, recent genome-wide association studies have suggested potential targets for immunomodulating agents, stressing the need for the identification of specific biomarkers of immune activity. In this work, we aim to review current evidence and recent progress, including the more recent use of omics techniques, in the identification of potential biomarkers for immune monitoring in IgAN and MN.

Implications of Sphingolipid Metabolites in Kidney Diseases

Sphingolipids, which act as a bioactive signaling molecules, are involved in several cellular processes such as cell survival, proliferation, migration and apoptosis. An imbalance in the levels of sphingolipids can be lethal to cells. Abnormalities in the levels of sphingolipids are associated with several human diseases including kidney diseases. Several studies demonstrate that sphingolipids play an important role in maintaining proper renal function. Sphingolipids can alter the glomerular filtration barrier by affecting the functioning of podocytes, which are key cellular components of the glomerular filtration barrier. This review summarizes the studies in our understanding of the regulation of sphingolipid signaling in kidney diseases, especially in glomerular and tubulointerstitial diseases, and the potential to target sphingolipid pathways in developing therapeutics for the treatment of renal diseases.

Integration of genetic and histopathology data in interpretation of kidney disease

For many years renal biopsy has been the gold standard for diagnosis in many forms of kidney disease. It provides rapid, accurate and clinically useful information in most individuals with kidney disease. However, in recent years, other diagnostic modalities have become available that may provide more detailed and specific diagnostic information in addition to, or instead of, renal biopsy. Genomics is one of these modalities. Previously prohibitively expensive and time consuming, it is now increasingly available and practical in a clinical setting for the diagnosis of inherited kidney disease. Inherited kidney disease is a significant cause of kidney disease, in both the adult and paediatric populations. While individual inherited kidney diseases are rare, together they represent a significant burden of disease. Because of the heterogenicity of inherited kidney disease, diagnosis and management can be a challenge and often multiple diagnostic modalities are needed to arrive at a diagnosis. We present updates in genomic medicine for renal disease, how genetic testing integrates with our knowledge of renal histopathology and how the two modalities may interact to enhance patient care.

Significance of subepithelial deposits in patients diagnosed with IgA nephropathy

Subepithelial deposits are observed in rare adult IgA nephropathy (IgAN) cases and are a key diagnostic finding in IgA-dominant infection-related glomerulonephritis (IgA-IRGN). Sometimes, it is difficult to distinguish IgA-IRGN from IgAN without a precise clinical history. We hypothesized that some IgA-IRGN cases might be diagnosed as IgAN with subepithelial deposits (IgAN-SD) and aimed to clarify the significance of subepithelial deposits in patients diagnosed with IgAN. We examined 464 patients diagnosed with IgAN at Nagasaki University Hospital and affiliated hospitals between 1996 and 2013. The differences in clinicopathological findings between IgAN-SD and IgAN with no subepithelial deposits (IgAN-NSD) were investigated. In addition to clinical data and typical IgAN pathological features, we analyzed complement levels, immunoglobulin localization, light chain staining patterns, and intramembranous deposits. There were 214 men and 250 women with a mean age of 38.8 ± 18.3 years. Subepithelial deposition was observed in 51 patients (11%). Compared to patients with IgAN-NSD, those with IgAN-SD had significantly lower mean serum protein (6.4 g/dL vs. 6.7 g/dL; p = 0.02), albumin (3.7 g/dL vs. 3.9 g/dL; p = 0.02), and complement (C3) (94 mg/dL vs. 103 mg/dL; p = 0.02) levels. Diffuse mesangial hypercellularity (M) (65% vs. 45%; p<0.01), endocapillary hypercellularity: (E) (43% vs. 28%; p = 0.03), and IgA staining in the glomerular capillary wall (22% vs. 8%; p<0.01) were more common in patients with IgAN-SD. The incidence of light chain lambda predominance was lower in patients with IgAN-SD (47% vs. 63%; p = 0.03). Hump-shaped subepithelial deposits and intramembranous deposits were observed in nine and 17 patients with IgAN-SD, respectively. Patients with IgAN-SD tended to have the characteristics of IgA-IRGN rather than IgAN-NSD. Since the therapeutic strategies for IgA-IRGN differ from those for IgAN, we should review the clinical history and pay careful attention to the clinical course in cases with atypical findings, such as subepithelial deposits.