Dissecting the histological features of lupus nephritis highlights new common patterns of injury in class III/IV.

OBJECTIVE: The International Society of Nephrology/Renal Pathology Society classification is the gold standard for the characterisation of lupus nephritis (LN) on renal biopsy, with therapeutic repercussions. Its recent revision simplified the current class subdivisions, eliminating the S/G forms of class IV, although data on a possible pathogenetic/clinical value of this subdivision are still contradictory. METHODS: 353 renal biopsies from Belimumab International Study in LN were assessed through central pathology review. Univariate logistic models and a decision tree were performed on 314 adequate biopsies to evaluate the impact of histological features on focal/diffuse classes. Removing class I/II (n=6) and 'pure' class V (n=34), principal component analysis (PCA) and heatmap were used to explore similarities among III, IVS and IVG biopsies either incorporating or not the mixed classes (+V, n=274). Finally, a method aimed at partitioning the cases into k clusters based on their similarity (KMeans), was used to study features from the cohort of 'pure' class III/IVS/IVG cases (n=214) to determine alternative subdivisions based on phenotypic data. RESULTS: Segmental endocapillary hypercellularity (EH) was prevalent in class III, global EH, wire loops, hyaline thrombi and double contours were hallmarks of class IVG, with IVS cases showing intermediate characteristics. Heatmap and PCA confirmed the segregation of these features among classes, showing better segregation for focal/diffuse LN as compared with the mixed classes (+V). KMeans revealed the presence of two main clusters, membranoproliferative-like (n=83) or vasculitis-like (n=131). CONCLUSIONS: This study reveals new phenotypic forms of LN surpassing the traditional classes as determined by the current classification. Future validation and confirmation are required to confirm these findings.

Reproducibility of the Oxford classification of immunoglobulin A nephropathy, impact of biopsy scoring on treatment allocation and clinical relevance of disagreements: evidence from the VALidation of IGA study cohort.

BACKGROUND: The VALidation of IGA (VALIGA) study investigated the utility of the Oxford Classification of immunoglobulin A nephropathy (IgAN) in 1147 patients from 13 European countries. Methods. Biopsies were scored by local pathologists followed by central review in Oxford. We had two distinct objectives: to assess how closely pathology findings were associated with the decision to give corticosteroid/immunosuppressive (CS/IS) treatments, and to determine the impact of differences in MEST-C scoring between central and local pathologists on the clinical value of the Oxford Classification. We tested for each lesion the associations between the type of agreement (local and central pathologists scoring absent, local present and central absent, local absent and central present, both scoring present) with the initial clinical assessment, as well as long-term outcomes in those patients who did not receive CS/IS. RESULTS: All glomerular lesions (M, E, C and S) assessed by local pathologists were independently associated with the decision to administer CS/IS therapy, while the severity of tubulointerstitial lesions was not. Reproducibility between local and central pathologists was moderate for S (segmental sclerosis) and T (tubular atrophy/interstitial fibrosis), and poor for M (mesangial hypercellularity), E (endocapillary hypercellularity) and C (crescents). Local pathologists found statistically more of each lesion, except for the S lesion, which was more frequent with central review. Disagreements were more likely to occur when the proportion of glomeruli affected was low. The M lesion, assessed by central pathologists, correlated better with the severity of the disease at presentation and discriminated better with outcomes. In contrast, the E lesion, evaluated by local pathologists, correlated better with the clinical presentation and outcomes when compared with central review. Both C and S lesions, when discordant between local and central pathologists, had a clinical phenotype intermediate to double absent lesions (milder disease) and double present (more severe). CONCLUSION: We conclude that differences in the scoring of MEST-C criteria between local pathologists and a central reviewer have a significant impact on the prognostic value of the Oxford Classification. Since the decision to offer immunosuppressive therapy in this cohort was intimately associated with the MEST-C score, this study indicates a need for a more detailed guidance for pathologists in the scoring of IgAN biopsies.

Revision of the International Society of Nephrology/Renal Pathology Society classification for lupus nephritis: clarification of definitions, and modified National Institutes of Health activity and chronicity indices.

We present a consensus report pertaining to the improved clarity of definitions and classification of glomerular lesions in lupus nephritis that derived from a meeting of 18 members of an international nephropathology working group in Leiden, Netherlands, in 2016. Here we report detailed recommendations on issues for which we can propose adjustments based on existing evidence and current consensus opinion (phase 1). New definitions are provided for mesangial hypercellularity and for cellular, fibrocellular, and fibrous crescents. The term "endocapillary proliferation" is eliminated and the definition of endocapillary hypercellularity considered in some detail. We also eliminate the class IV-S and IV-G subdivisions of class IV lupus nephritis. The active and chronic designations for class III/IV lesions are replaced by a proposal for activity and chronicity indices that should be applied to all classes. In the activity index, we include fibrinoid necrosis as a specific descriptor. We also make recommendations on issues for which there are limited data at present and that can best be addressed in future studies (phase 2). We propose to proceed to these investigations, with clinicopathologic studies and tests of interobserver reproducibility to evaluate the applications of the proposed definitions and to classify lupus nephritis lesions.

The putative role of MALDI-MSI in the study of Membranous Nephropathy.

Membranous Nephropathy (MN) is an immunocomplex mediated renal disease that represents one of the most frequent glomerulopathies worldwide. This glomerular disease can manifest as primary (idiopathic) or secondary and this distinction is crucial when choosing the most appropriate course of treatment. In secondary cases, the best strategy involves treating the underlying disease, whereas in primary forms, the identification of confirmatory markers of the idiopathic etiology underlining the process is requested by clinicians. Among those currently reported, the positivity to circulating antigens (PLA2R, IgG4 and THSD7A) was demonstrated in approximately 75% of iMN patients, while approximately 1 in 4 patients with iMN still lack a putative diagnostic marker. Ultimately, the discovery of biomarkers to help further stratify these two different forms of glomerulopathy seems mandatory. Here, MALDI-MSI was applied to FFPE renal biopsies from histologically diagnosed primary and secondary MN patients (n=20) in order to detect alterations in their tissue proteome. MALDI-MSI was able to generate molecular signatures of primary and secondary MN, with one particular signal (m/z 1459), identified as Serine/threonine-protein kinase MRCK gamma, being over-expressed in the glomeruli of primary MN patients with respect to secondary MN. Furthermore, a number of signals that could differentiate the different forms of iMN that were positive to PLA2R or IgG4 were detected, as well as a further set of signals (m/z 1094, 1116, 1381 and 1459) that could distinguish these patients from those who were negative to both. These signals could potentially represent future targets for the further stratification of iMN patients. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Risk factors for progression in children and young adults with IgA nephropathy: an analysis of 261 cases from the VALIGA European cohort.

BACKGROUND: There is a need for early identification of children with immunoglobulin A nephropathy (IgAN) at risk of progression of kidney disease. METHODS: Data on 261 young patients [age <23 years; mean follow-up of 4.9 (range 2.5-8.1) years] enrolled in VALIGA, a study designed to validate the Oxford Classification of IgAN, were assessed. Renal biopsies were scored for the presence of mesangial hypercellularity (M1), endocapillary hypercellularity (E1), segmental glomerulosclerosis (S1), tubular atrophy/interstitial fibrosis (T1-2) (MEST score) and crescents (C1). Progression was assessed as end stage renal disease and/or a 50 % loss of estimated glomerular filtration rate (eGFR) (combined endpoint) as well as the rate of renal function decline (slope of eGFR). Cox regression and tree classification binary models were used and compared. RESULTS: In this cohort of 261 subjects aged <23 years, Cox analysis validated the MEST M, S and T scores for predicting survival to the combined endpoint but failed to prove that these scores had predictive value in the sub-group of 174 children aged <18 years. The regression tree classification indicated that patients with M1 were at risk of developing higher time-averaged proteinuria (p < 0.0001) and the combined endpoint (p < 0.001). An initial proteinuria of ≥0.4 g/day/1.73 m2 and an eGFR of <90 ml/min/1.73 m2 were determined to be risk factors in subjects with M0. Children aged <16 years with M0 and well-preserved eGFR (>90 ml/min/1.73 m2) at presentation had a significantly high probability of proteinuria remission during follow-up and a higher remission rate following treatment with corticosteroid and/or immunosuppressive therapy. CONCLUSION: This new statistical approach has identified clinical and histological risk factors associated with outcome in children and young adults with IgAN.

α-1-Antitrypsin detected by MALDI imaging in the study of glomerulonephritis: Its relevance in chronic kidney disease progression.

Idiopathic glomerulonephritis (GN), such as membranous glomerulonephritis, focal segmental glomerulosclerosis (FSGS), and IgA nephropathy (IgAN), represent the most frequent primary glomerular kidney diseases (GKDs) worldwide. Although the renal biopsy currently remains the gold standard for the routine diagnosis of idiopathic GN, the invasiveness and diagnostic difficulty related with this procedure highlight the strong need for new diagnostic and prognostic biomarkers to be translated into less invasive diagnostic tools. MALDI-MS imaging MALDI-MSI was applied to fresh-frozen bioptic renal tissue from patients with a histological diagnosis of FSGS (n = 6), IgAN, (n = 6) and membranous glomerulonephritis (n = 7), and from controls (n = 4) in order to detect specific molecular signatures of primary glomerulonephritis. MALDI-MSI was able to generate molecular signatures capable to distinguish between normal kidney and pathological GN, with specific signals (m/z 4025, 4048, and 4963) representing potential indicators of chronic kidney disease development. Moreover, specific disease-related signatures (m/z 4025 and 4048 for FSGS, m/z 4963 and 5072 for IgAN) were detected. Of these signals, m/z 4048 was identified as α-1-antitrypsin and was shown to be localized to the podocytes within sclerotic glomeruli by immunohistochemistry. α-1-Antitrypsin could be one of the markers of podocyte stress that is correlated with the development of FSGS due to both an excessive loss and a hypertrophy of podocytes.

Tubulointerstitial lesions in lupus nephritis: International multicentre study in a large cohort of patients with repeat biopsy.

BACKGROUND: The glomerulocentric International Society of Nephrology/Renal Pathology Society (ISN/RPS) classification is the gold standard for the evaluation of lupus nephritis, while tubulointerstitial (TIN) parameters are often under-recognized in pathological reports. METHODS: Renal biopsies from 142 patients who underwent repeat biopsy (RB) were evaluated for the following histological parameters: (i) inflammatory interstitial infiltrates; (ii) interstitial fibrosis; (iii) tubulitis; and (iv) tubular atrophy. The inter-relationships between the four TIN variables were explored by multivariate analysis. A linear mixed model was used to investigate the potential impact of TIN variables on eGFR and proteinuria at the two biopsy occasions. RESULTS: The study showed that moderate-severe lesions were not so frequent at the reference biopsy, but more extensively represented upon RB. A strong association was found between the two inflammatory indices and between those related to chronic damage, while the relationship with the ISN/RPS classification was present at RB. If class IV-G was the most related with TIN (especially at RB), the existence of primary TIN in class II patients was also confirmed. Finally, our results support the hypothesis that tubulitis is an independent predictive factor for eGFR. CONCLUSIONS: We recommend that the standard histological evaluation of SLE nephritis also includes TIN features.

The Revisited Classification of GN in SLE at 10 Years: Time to Re-Evaluate Histopathologic Lesions.

Over 10 years have passed since the latest revision of the histopathologic classification of lupus nephritis. This revision was a significant improvement compared with the previous version, mainly because of clearer and more concise definitions and the elimination of mixed subclasses. Despite these improvements, there are still some difficulties in the classification for lupus nephritis, many of which are in the definitions provided. In this review, we focus on the difficulties surrounding the evaluation of classes III and IV lesions, particularly the definitions of endocapillary and extracapillary proliferation, the use of the terms endocapillary proliferation and hypercellularity, the clinical relevance of segmental and global subdivision in class IV, and the value of distinguishing lesions that indicate activity and chronicity. Vascular and tubulointerstitial lesions are also discussed. Furthermore, we give an overview of the history of the classification to provide background on the origin and development of the definitions in lupus nephritis. The issues raised in this review as well as the suggestions for improvements may assist with a revision of the lupus nephritis classification in the near future.

Renal function and ear, nose, throat involvement in anti-neutrophil cytoplasmic antibody-associated vasculitis: prospective data from the European Vasculitis Society clinical trials.

OBJECTIVE: We investigated whether ENT involvement is associated with renal biopsy findings and renal function in patients with ANCA-associated vasculitis (AAV). METHODS: Newly diagnosed AAV patients derived from three international, multicentre trials were included. To investigate an association between ENT involvement and estimated glomerular filtration rate (eGFR) at diagnosis and 5-year follow-up, we performed multivariable regression analyses including clinical and histopathological parameters. To investigate whether our findings are specific to ENT involvement, we performed comparable analyses between eGFR and other early disease manifestations (arthralgia/arthritis, cutaneous and lung involvement). RESULTS: One hundred and eighty-five of the 414 patients had ENT involvement. The mean presenting eGFR of patients with and without ENT involvement was 39.16 and 23.88 ml/min/1.73 m(2), respectively (P < 0.001). Mean eGFR increased by 6.76 ml/min/1.73 m(2) with each added ENT symptom (P = 0.007). Patients with ENT involvement had less interstitial fibrosis and tubular atrophy and a prognostically more favourable histopathological class on renal biopsy examination. Multivariable regression analyses correcting for clinical and histopathological parameters showed that ENT involvement is associated with both baseline and 5-year follow-up eGFR. There were no associations between baseline and 5-year follow-up eGFR and arthralgia/arthritis, cutaneous or lung involvement, suggesting that our findings are specific to ENT involvement. CONCLUSION: The presence of ENT involvement in AAV patients is associated with prognostically favourable renal biopsy findings and better renal function. These results indicate that there may be different phenotypes of AAV defined by ENT involvement.

Twenty-five years of RENHIS: a history of histopathological studies within EUVAS.

In the early 1990s, an international working group of experienced renal pathologists, the Renal Histology group, set up a scoring system for biopsies with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis. This scoring system subdivided glomerular, interstitial and vascular lesions and served as a tool for the evaluation of all renal biopsies from studies of the European Vasculitis Study Group (EUVAS). Histopathological studies gave new insights into the prediction of renal outcome in patients with ANCA-associated glomerulonephritis. Percentage of normal glomeruli and a selected number of interstitial parameters were reliable predictors of long-term follow-up glomerular filtration rate in all studies. Out of these results, a histopathological classification distinguishing focal, crescentic, mixed and sclerotic classes of ANCA-associated glomerulonephritis was developed. Until today, 13 studies have validated this classification system. Future studies will try to determine if and how renal histology could be helpful in guiding treatment of ANCA-associated glomerulonephritis.