Development and Validation of a Multiclass Model Defining Molecular Archetypes of Kidney Transplant Rejection: A Large Cohort Study of the Banff Human Organ Transplant Gene Expression Panel.

Gene expression profiling from formalin-fixed paraffin-embedded (FFPE) renal allograft biopsies is a promising approach for feasibly providing a molecular diagnosis of rejection. However, large-scale studies evaluating the performance of models using NanoString platform data to define molecular archetypes of rejection are lacking. We tested a diverse retrospective cohort of over 1400 FFPE biopsy specimens, rescored according to Banff 2019 criteria and representing 10 of 11 United Network of Organ Sharing regions, using the Banff Human Organ Transplant panel from NanoString and developed a multiclass model from the gene expression data to assign relative probabilities of 4 molecular archetypes: No Rejection, Antibody-Mediated Rejection, T Cell-Mediated Rejection, and Mixed Rejection.

Clinicopathologic Spectrum of Lysozyme-Associated Nephropathy.

Introduction: Lysozyme-associated nephropathy (LyN), a rare cause of kidney injury in patients with chronic myelomonocytic leukemia (CMML), has not been well described to date. We report the clinicopathologic spectrum of LyN from a multi-institutional series.

Method: We identified 37 native kidney biopsies with LyN and retrospectively obtained clinicopathologic data.

A multi-center retrospective cohort study defines the spectrum of kidney pathology in Coronavirus 2019 Disease (COVID-19).

Kidney failure is common in patients with Coronavirus Disease-19 (COVID-19), resulting in increased morbidity and mortality. In an international collaboration, 284 kidney biopsies were evaluated to improve understanding of kidney disease in COVID-19. Diagnoses were compared to five years of 63,575 native biopsies prior to the pandemic and 13,955 allograft biopsies to identify diseases that have increased in patients with COVID-19.

NELL1 is a target antigen in malignancy-associated membranous nephropathy.

Patients with membranous nephropathy have an increased risk of malignancy compared to the general population, but the target antigen for malignancy-associated membranous nephropathy is unknown. To explore this, we utilized mass spectrometry for antigen discovery in malignancy-associated membranous nephropathy examining immune complexes eluted from frozen kidney biopsy tissue using protein G bead immunoglobulin capture. Antigen discovery was performed comparing cases of membranous nephropathy of unknown and known type.

A practical approach to the pathology of renal intratubular casts.

The identification and proper characterization of pathologic renal intratubular casts can be an arduous task, especially since they often admixed with non-pathologic casts, obfuscating debris and inflammation. The list of pathologic intratubular casts is long, and they can be easily missed or misdiagnosed without a thorough understanding of their pathophysiology and morphologic variety. Correct characterization of tubular casts is important since each cast type has a unique pathogenic mechanism, with specific treatment and prognostic implications.

Hemolysis-associated hemoglobin cast nephropathy results from a range of clinicopathologic disorders.

Intravascular hemolysis is relatively rare but can lead to acute kidney injury (AKI), from increased destruction of erythrocytes and release of free hemoglobin. Since hemolysis and hemoglobinuria are known causes of acute kidney injury we sought to define clinicopathologic findings and outcomes of patients with hemolysis-associated hemoglobin cast nephropathy through a retrospective analysis of 27 cases. The mean patient age was 47 years (range 19-79) and the female-to-male ratio was 1.

LDL Receptor-Related Protein 2 (Megalin) as a Target Antigen in Human Kidney Anti-Brush Border Antibody Disease.

Primary renal tubulointerstitial disease resulting from proximal tubule antigen-specific antibodies and immune complex formation has not been well characterized in humans. We report a cohort of patients with a distinct, underappreciated kidney disease characterized by kidney antibrush border antibodies and renal failure (ABBA disease). We identified ten patients with ABBA disease who had a combination of proximal tubule damage, IgG-positive immune deposits in the tubular basement membrane, and circulating antibodies reactive with normal human kidney proximal tubular brush border.

A rare case of renal thrombotic microangiopathy associated with Castleman's disease.

Background: Castleman's disease (CD) is an uncommon, heterogeneous lympho-proliferative disorder leading to high circulating levels of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF). Renal involvement has been only described in a limited number of small studies. Herein, we report a rare case of renal thrombotic microangiopathy (TMA) associated with CD and investigate the podocyte expression of VEGF in the renal biopsy prior to initiation of treatment.

Clinicopathologic Features of Membranous-Like Glomerulopathy With Masked IgG Kappa Deposits.

Introduction: Ig deposits identified on renal biopsy samples by paraffin immunofluorescence that show negative staining by routine immunofluorescence on frozen tissue have become known as "masked" deposits. Membranous-like glomerulopathy with masked IgG kappa (κ) deposits is a recently recognized pattern of immune complex deposition characterized by masked deposits that show IgG κ restriction and are subepithelial and mesangial by electron microscopy. Based on the frequent presence of C3-only staining by routine immunofluorescence microscopy (IF), these cases could be misdiagnosed as C3 glomerulonephritis in the absence of paraffin immunofluorescence evaluation.

THSD7A staining of membranous glomerulopathy in clinical practice reveals cases with dual autoantibody positivity.

Thrombospondin type I domain-containing 7A (THSD7A) is a known antigenic target of autoantibodies leading to primary membranous glomerulopathy and was reported to account for ~10% of phospholipase A2 receptor (PLA2R)-negative membranous glomerulopathy. It has been proposed that PLA2R and THSD7A autoantibodies are mutually exclusive in membranous glomerulopathy. We validated an immunohistochemical assay to investigate for THSD7A-associated membranous glomerulopathy and utilized it in 258 consecutive native kidney biopsies, which showed membranous glomerulopathy in our laboratory, with the exception of membranous lupus nephritis.

Vascular mesangial channels in human nodular diabetic glomerulopathy.

The presence of vascular mesangial channels has been reported in idiopathic nodular glomerulosclerosis and diabetic glomerulopathy. However, only limited information on the morphology and immunohistochemical phenotype of these channels is available. This study aims to describe the light and electron microscopic features of these channels and delineate their immunohistochemical phenotype.

Collagenofibrotic glomerulopathy.

Background: Collagenofibrotic glomerulopathy is a rare renal disease of unknown etiology that is secondary to deposition of type III collagen within the glomerulus. Only rare case series exist in the literature.

Methods: Renal biopsies diagnosed with collagenofibrotic glomerulopathy were prospectively collected at the Center for Renal and Urological Pathology (AAK) (Chennai, Tamil Nadu, India) from 2012 to 2015.

Defining the spectrum of immunoglobulin A-dominant/codominant glomerular deposition in diabetic nephropathy.

In patients with diabetic nephropathy (DN), the spectrum of immunoglobulin A (IgA)-dominant/codominant glomerular deposition (IgAGD) has not been addressed in the literature. The aim of our study is to detail the clinicopathological and outcome findings in patients with DN and IgAGD. Our database was retrospectively searched over a 10-year period for patients with DN and IgAGD.

Histopathologic findings associated with APOL1 risk variants in chronic kidney disease.

The effects of nephropathy risk variants in the apolipoprotein L1 gene (APOL1) on renal histopathology in African Americans with arterionephrosclerosis or putative 'hypertension-associated' nephropathy are unknown. APOL1 genotype-phenotype correlations were performed in a blinded manner from renal biopsies in 196 self-reported African Americans with arterionephrosclerosis on kidney biopsy at a large national nephropathology practice. Subjects had chronic kidney disease without nephrotic syndrome.

Membranous-like glomerulopathy with masked IgG kappa deposits.

The diagnostic classification of glomerulonephritis is determined by the interplay of changes seen using light, immunofluorescence, and electron microscopy of the renal biopsy. Routine direct immunofluorescence on fresh tissue is currently considered the gold standard for the detection and characterization of immune deposits. We recently found a peculiar form of glomerular immune complex deposition in which masked deposits required an antigen-retrieval step to be visualized.

Phospholipase A2 receptor staining in pediatric idiopathic membranous glomerulopathy.

Background: Membranous glomerulopathy, though typically a disease of adults, does occur in children. Antiphospholipase A2 receptor (PLA2R) autoantibodies have recently been implicated as a causative agent in most cases of adult primary (idiopathic) membranous glomerulopathy. PLA2R staining of renal biopsies in two recent large case series of adults with primary membranous glomerulopathy showed a sensitivity of approximately 75 % for detecting primary membranous glomerulopathy.

Oxalate nephropathy and intravenous vitamin C.

Oxalate nephropathy is a rare condition characterized by extensive calcium oxalate deposition in the renal tubules, resulting in kidney injury. There are primary forms of the disease that arise from genetic mutation causing overproduction of oxalate. More commonly, this condition is seen as a secondary phenomenon.