DNAJB9-positive monotypic fibrillary glomerulonephritis is not associated with monoclonal gammopathy in the vast majority of patients

[Fibrillary glomerulonephritis]

Fibrillary glomerulonephritis (FGN) is a glomerular disease described since 1977, with a prevalence in renal biopsies of less than 1%. It presents as renal failure, proteinuria, haematuria and hypertension in middle-aged adults. It is defined histologically, using light microscopy, which reveals organised deposits of fibrils measuring around 20nm, which are negative for Congo red staining. Electron microscopy, the first gold standard for diagnosis, has now been superseded by immunohistochemistry using the anti-DNAJB9 antibody. The discovery of this molecule has revolutionised the diagnosis of GNF, thanks to its excellent sensitivity and specificity (98% and 99% respectively). The association of GNF with hepatitis C virus, autoimmune diseases, neoplasia or haemopathy is debated. Renal prognosis is guarded, with 50% of patients progressing to end-stage renal failure within 2 to 4years of diagnosis. In the absence of randomised controlled trials, the recommended treatment is based on nephroprotective measures, corticosteroid therapy and possibly a second-line immunosuppressant such as rituximab. After renal transplantation, recovery or recurrence is possible. The pathophysiology of the disease is still poorly understood, and further studies are needed.

Immunofluorescence Staining for IgG Subclass: Cause for Discrepancy in the Detection of IgG1

Introduction

Immunofluorescence (IF) staining for IgG subclasses plays an important role in the classification of kidney disease. However, widely used IgG subclass-specific antibodies are now commercially unavailable. Thus, we compared alternative antibodies for performing IgG subclass staining.

Methods

A total of 21 cases were stained by 3 different methods: direct IF using fluorescein isothiocyanate (FITC)-conjugated polyclonal antibodies against IgG1-4 (commercially unavailable method), direct IF using FITC-conjugated monoclonal antibodies (clones HP-6091, 6014, 6050, and 6025), indirect IF using monoclonal antibodies (clones HP-6069, 6002, 6050, and 6025), and FITC-conjugated polyclonal secondary antibody. For cases with discrepancy in IgG1 staining, additional direct IF using FITC-conjugated monoclonal antibody (clone 4E3) was performed.

Results

Of 21 cases, 11 (52%) had no staining for IgG1 by direct IF using the clone HP-6091 despite ≥1+ staining by the direct IF using polyclonal antibodies. Similarly, direct IF for IgG1 using the clone 4E3 had negative result in all 10 cases with available tissue. However, indirect IF for IgG1 using the clone HP-6069 had similar staining intensity (within 1 order of magnitude) as direct IF using the polyclonal antibodies (10 of 10). Results of IF for IgG2, IgG3, and IgG4 were similar in most cases.

Conclusion

The choice of antibodies influences the result of IgG subclass staining, especially for anti-IgG1 antibodies, in which 2 monoclonal antibodies (HP6091 and 4E3) appear less sensitive. Although this may be due to unaccounted variables and requires confirmation, our results may partially explain the difference in IgG1 staining in the literature and underscore the need for careful validation.

Kidney Biopsy Corner: Amyloidosis

Amyloidosis is an infiltrative disease caused by misfolded proteins depositing in tissues. Amyloid infiltrates the kidney in several patterns. There are, as currently described by the International Society of Amyloidosis, 14 types of amyloid that can involve the kidney, and these types may have different locations or clinical settings. Herein we report a case of AA amyloidosis occurring in a 24-year-old male with a history of intravenous drug abuse and provide a comprehensive review of different types of amyloids involving the kidney.

Heavy Chain/Light Chain Antibody Immunofluorescence to Identify Monoclonal Plasma Cells in a Case of Plasma Cell-Rich Acute Interstitial Nephritis

Heavy/light chain (HLC) antibodies can be used to quantify intact HLC pairs. In immunofluorescence studies, they allow differentiation of monoclonal versus polyclonal immunoglobulin deposits in kidney diseases that occur in the setting of monoclonal gammopathy. Here, we present a case of a patient with acute kidney injury with first kidney biopsy suggestive of acute interstitial nephritis with a polymorphous infiltrate of plasma cells. Routine immunofluorescence did not show a monotypic plasma cell infiltrate. Serum protein electrophoresis and immunofixation revealed monoclonal immunoglobulin A (IgA) lambda. She improved with steroid therapy, but kidney function worsened after steroids were stopped. She underwent a second kidney biopsy, which showed plasma cell-rich interstitial infiltrate with a population of IgA lambda-restricted plasma cells on routine immunofluorescence. In light of this finding, Hevylite HLC antibody was used to reassess the first biopsy, which confirmed the presence of a population of plasma cells with IgA lambda restriction. Because of the presence of monotypic plasma cells, anti-CD38 monoclonal antibody (daratumumab) was initiated.

Fibrillary Glomerulonephritis and Monoclonal Gammopathy: Potential Diagnostic Challenges

Fibrillary glomerulonephritis (FGN) is a rare glomerular disease featured by the randomly arranged 12- to 24-nm fibrils under electron microscopy (EM). Up to 10% of FGN patients have monoclonal gammopathy. However, distinguishing between FGN as monoclonal gammopathy of renal significance (MGRS) and FGN from other causes with incidental monoclonal gammopathy of undetermined significance (MGUS) can be challenging, as the current way of demonstrating monoclonality is flawed due to (1) the suboptimal sensitivity of kappa staining by immunofluorescence in frozen tissue (IF-F) as compared to pronase-digested paraffin sections (IF-P), causing incorrect labeling of light chain restriction; (2) the unavailability of immunoglobulin G (IgG) subtyping in some centers; and (3) the unavailability of tests demonstrating the monoclonality of highly variable VH or VL domains in immunoglobulin structures in clinical use. The discovery of DnaJ homolog subfamily B member 9 (DNAJB9) allows diagnosis for FGN with less reliance on EM, and the summary of recent studies revealed that genuine MGRS is extremely rare among FGN. Further research integrating IF-P, IgG subtyping, VH or VL domain monoclonality confirmation, and DNAJB9 as diagnostic modalities, with corresponding clinical data including treatment response and prognosis, is required for a better understanding of this subject.

Novel approaches beyond standard immunofluorescence for kidney biopsies

PURPOSE OF REVIEW

Immunofluorescence on frozen tissue (IF-F) utilizing antibodies against immunoglobulin (Ig) heavy and light chains (IgA, IgG and IgM, kappa and lambda) and components of classical and alternative complement pathways (C1q, C3c and C4) is the standard of renal pathology. However, conventional IF-F has limitations, particularly in nephropathies associated with organized and/or monoclonal Ig deposits. This review will discuss new applications of established methods beyond conventional IF-F and recent novel immunohistochemical methods.

RECENT FINDINGS

The combined application of paraffin immunofluorescence (IF-P) and IgG subtype staining excluded monotypic deposits in 62-66% of DNA J homolog subfamily B member 9-associated fibrillary glomerulonephritis (FGN) with apparent monotypic deposits by IF-F, whereas IF-P unmasks IgG deposits in a subset of cases of immunotactoid glomerulopathy. A novel IF technique targeting epitopes at the junction of the Ig heavy and light chains was introduced and unmasked polytypic deposits in a subset of glomerulonephritis with apparent monotypic deposits on IF-F. A recent study described the successful application of co-detection by indexing (CODEX) multiplexed IF to visualize more than a dozen target antigens within a single kidney tissue section. Finally, immunohistochemical protocols for detection of the novel antigens in membranous nephropathy have already entered the clinical practice of renal pathology.

SUMMARY

Novel ancillary techniques in renal pathology have the potential to significantly enhance our ability to evaluate renal biopsies.

RNA-based immunoglobulin repertoire sequencing is a new tool for the management of monoclonal gammopathy of renal (kidney) significance

The diagnostic approach of monoclonal gammopathy of renal significance is based on the detection of a monoclonal immunoglobulin in the blood and urine, and the identification of the underlying clone through bone marrow and/or peripheral blood cytologic and flow cytometry analysis. However, the monoclonal component and its corresponding clone may be undetectable using these routine techniques. Since clone identification is the cornerstone for guiding therapy and assessing disease response, more sensitive methods are required. We recently developed a high-throughput sequencing assay from bone marrow mRNA encoding immunoglobulins (RACE-RepSeq). This technique provides both full-length V(D)J region (variable, diversity and joining genes that generate unique receptors as antigen receptors) of the monoclonal immunoglobulin and the dominant immunoglobulin repertoire. This allows analysis of mutational patterns, immunoglobulin variable gene frequencies and diversity due to somatic hypermutation. Here, we evaluated the diagnostic performance of RACE-RepSeq in 16 patients with monoclonal-associated kidney lesions, and low serum monoclonal immunoglobulin and free light chain levels at diagnosis. Bone marrow immunohistochemical analysis was negative in all 11 patients so tested and 7 of 12 patients had no detectable clone matching the kidney deposits using flow cytometry analysis. By contrast, RACE-RepSeq detected a dominant clonal light chain sequence of matched isotype with respect to kidney deposits in all patients. Thus, high throughput mRNA sequencing appears highly sensitive to detect subtle clonal disorders in monoclonal gammopathy of renal significance and suggest this novel approach could help improve the management of this kidney disease.

A Fresh Perspective on Monoclonal Gammopathies of Renal Significance

Monoclonal gammopathies of renal significance (MGRS) encompass a remarkable variety of kidney diseases that result from intrinsic nephrotoxic properties of certain monoclonal Igs or their subunits. Effective disease-modifying treatments rely on the targeting of a malignant B-cell clone that may be demonstrable but often is quite hypothetical. Hence, convincing arguments for the genuine monoclonal character of the causative mono-isotypic Ig tissue deposits is needed for design of appropriate treatment strategies. The purpose of this article was to critically analyze distinct situations of suspected MGRS that occur in the practice of pathologists, nephrologists, hematologists, and immunologists. A particular focus of interest is the group of conditions known as proliferative glomerulonephritis with mono-isotypic immunoglobulin deposits (PGNMIDs), which illustrates the difficulties and ambiguities surrounding a definitive assignment of MGRS status.

DNA J homolog subfamily B member 9 and other advances in fibrillary glomerulonephritis

PURPOSE OF REVIEW

Fibrillary glomerulonephritis (FGN) involves ∼1% of native kidney biopsies and is characterized by glomerular deposition of fibrils larger than amyloid (12-24 nm diameter) composed of polyclonal immunoglobulin G (IgG). The recent discovery of DNA J homolog subfamily B member 9 (DNAJB9) in FGN glomerular deposits has contributed a specific and sensitive biomarker, informing morphologic classification and pathogenesis. This review will consider contemporary FGN incidence and genetics, pathogenesis, (lack of) paraprotein association, variants, treatment, and transplantation.

RECENT FINDINGS

DNAJB9 tissue assays have enabled the identification of morphologic variants and improved classification of fibrillary-like glomerular diseases. Together with paraffin immunofluorescence and IgG subclass studies, these have established that FGN is only rarely monoclonal and these patients usually do not have an monoclonal gammopathy. The discovery of DNAJB9 opens new avenues of investigation into FGN pathogenesis, especially those of the unfolded protein response. Treatment for FGN remains empiric, with some encouraging data on rituximab-based therapy. Transplantation is a good option for patients progressing to end-stage kidney disease.

SUMMARY

Advances building on the discovery of DNAJB9 in FGN should lead to long-term evolution in targeted treatment and outcome of this glomerular disease.

The Clone Wars: Diagnosing and Treating Dysproteinemic Kidney Disease in the Modern Era

Dysproteinemic kidney diseases are disorders that occur as the result of lymphoproliferative (B cell or plasma cell) disorders that cause kidney damage via production of nephrotoxic monoclonal immunoglobulins or their components. These monoclonal immunoglobulins have individual physiochemical characteristics that confer specific nephrotoxic properties. There has been increased recognition and revised characterization of these disorders in the last decade, and in some cases, there have been substantial advances in disease understanding and treatments, which has translated to improved patient outcomes. These disorders still present challenges to nephrologists and patients, since they are rare, and the field of hematology is rapidly changing with the introduction of novel testing and treatment strategies. In this review, we will discuss the clinical presentation, kidney biopsy features, hematologic characteristics and treatment of dysproteinemic kidney diseases.

Proliferative Glomerulonephritis With Fibrils, Monoclonal κ Light Chain, and C3 Deposits

There is increasing recognition of monoclonal gammopathy as a cause of proliferative glomerulonephritis (GN), including cases in which glomerular deposition of monoclonal immunoglobulin is demonstrated. Recently, proliferative GN with monoclonal immunoglobulin deposits (PGNMID) has incorporated a light chain variant of the disease (termed PGNMID-LC). Intriguingly, glomerular co-deposition of C3 is found in addition to monotypic light chain, implying complement activation via the alternative pathway (AP). We present a unique case of proliferative GN in a 42-year-old man who presented with nephrotic syndrome and was found to have κ light chain multiple myeloma. Immune staining of the glomerulus was positive only for κ light chain and C3, with the striking appearance of nonamyloid fibrils on electron microscopy. Following clonally targeted therapy for myeloma, the renal clinical abnormalities resolved completely. We present detailed molecular studies for light chain and complement and consider local mechanisms whereby monoclonal κ light chain fibrils may have triggered AP activation within the glomerulus.

Diagnostic Approach to Glomerulonephritis With Fibrillar IgG Deposits and Light Chain Restriction

Introduction

The pathologic approach to glomerulonephritis (GN) with fibrillar IgG deposits and light chain restriction remains a diagnostic challenge.

Method

All GN with fibrillar deposits of IgG and apparent light chain restriction on standard immunofluorescence on frozen tissue (IF-F) accessioned at the Columbia Renal Pathology Laboratory from 2012 to 2019 were identified. Additional studies including staining for Congo red, DNAJB9, IgG subtypes, and immunofluorescence on pronase-digested paraffin sections (IF-P) were performed.

Result

Based on the results, biopsy samples were reclassified as polytypic DNAJB9-positive fibrillary glomerulonephritis (pFGN, n = 14), monotypic DNAJB9-positive FGN (mFGN, n = 7), GN with polytypic DNAJB9-negative fibrillar IgG deposits (n = 2), and GN with monotypic DNAJB9-negative fibrillar IgG deposits (n = 6). Among DNAJB9-positive FGN samples, IgG subtype staining was able to exclude monotypic deposits by demonstrating reactivity for ≥2 IgG subtypes (usually IgG1 and IgG4) in 67% (14 of 21), including 9 that would have been misclassified as monotypic by IF-F and IF-P alone. Monotypic DNAJB9-positive fibrillary glomerulonephritis (FGN) was not associated with monoclonal gammopathy in 5 of 6 patients. GN with monotypic DNAJB9-negative fibrillar IgG deposits exhibited focal parallel fibril alignment and frequent association with chronic lymphocytic leukemia, but lacked the diagnostic microtubules of immunotactoid GN.

Conclusion

A systematic diagnostic approach with ancillary techniques is essential for proper classification and assignment of monoclonal gammopathy of renal significance status in cases of GN with fibrillary IgG deposits and light chain restriction by IF-F.

Monoclonal Gammopathy of Renal Significance with Deposits of Peculiar Morphology and Injuries of Secondary Thrombotic Microangiopathy: A Case Report and Review of the Literature

We present the case of an 82-year-old woman diagnosed with monoclonal gammopathy of renal significance (MGRS) with the presence of different and peculiar kidney lesions, who began treatment with bortezomib and dexamethasone, presenting during her evolution a relapse. Although the bone marrow biopsy in this case showed plasma cells as pathologic clone and there was also a reduction after chemotherapeutic treatment, rituximab was proposed as a second line. We suspected that the relapse was possibly due to another precursor as B-cell or lymphoplasmacytic cell clone. We review the literature and suggest that the treatment for MGRS should be patient-tailored, preferably by consulting a multidisciplinary team. Future research is needed to better understand the disease course and establish the efficacy and safety of the therapeutic approach for the relapse of MGRS.

Multiple Myeloma-Associated Light Chain Amyloidosis and a Proposed Approach to Monoclonal Immunoglobulin-Associated Renal Disease

Many challenges remain in diagnosing monoclonal immunoglobulin-associated renal disease, despite widespread application of immunofluorescence (IF) and immunohistochemistry. Here, we report a newly diagnosed case of multiple myeloma with clinical suspicion of renal amyloidosis, which had negative IF staining for kappa and lambda light chains in the glomeruli. Although laser microdissection and mass spectrometry-based proteomic analysis have emerged as important tools for amyloid typing in the literature, such facilities are still not widely available in Asia. We propose that a clinicopathological algorithm for the evaluation of organized monoclonal renal deposits, together with a combined nephrological-haematological approach, will still be adequate to generate an unequivocal diagnosis in the majority of cases.

Fibrillary Glomerulonephritis and DnaJ Homolog Subfamily B Member 9 (DNAJB9)

Fibrillary GN (FGN) is a rare glomerular disease that is diagnosed based on the presence of fibrils in glomeruli. The fibrils are typically noncongophilic, randomly oriented, and measure 12–24 nm. Traditionally, electron microscopy (EM) has been an important tool to aid in the diagnosis of FGN by identifying the fibrils and to distinguish it from other entities that could mimic FGN. However, recently DnaJ homolog subfamily B member 9 (DNAJB9) has emerged as both a specific and sensitive biomarker in patients with FGN. It allows prompt diagnosis and alleviates reliance on EM. DNAJB9 is a cochaperone of heat shock protein 70 and is involved in endoplasmic reticulum protein-folding pathways. But its role in the pathogenesis of FGN remains elusive. DNAJB9 may act as a putative antigen or alternatively it may secondarily bind to misfolded IgG in the glomeruli. These hypotheses need future studies to elucidate the role of DNAJB9 in the pathogenesis of FGN. The treatment regimen for FGN has been limited due to paucity of studies. Most patients receive combination immunosuppressive regimens. Rituximab has been studied the most in FGN and it may delay disease progression. Prognosis of FGN remains poor and 50% require dialysis within 2 years of diagnosis. Despite its poor prognosis in native kidneys, the rate of recurrence post-transplantation is low (20%) and patient as well as allograft outcomes are similar to patients without FGN.