Immunofluorescence staining for immunoglobulin heavy chain/light chain on kidney biopsies is a valuable ancillary technique for the diagnosis of monoclonal gammopathy-associated kidney diseases

IgM Variant of Proliferative Glomerulonephritis With Monoclonal Immunoglobulin Deposits: A Case Series

RATIONALE & OBJECTIVE

Most deposits in proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) are of the IgG class. The IgM variant (PGNMID-IgM) is very rare, and data are mostly derived from single case reports or cases associated with B-cell lymphoproliferative disorders. We describe the clinicopathologic characteristics and outcomes among cases of PGNMID-IgM.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

23 PGNMID-IgM cases identified from kidney pathology archives. PGNMID-IgM was defined by glomerulonephritis with glomerular granular monotypic IgM deposits after excluding cryoglobulinemic glomerulonephritis and intracapillary monoclonal deposits disease.

FINDINGS

Seventy-eight percent of the cases were male, they had a median age of 72 years, and they had presented with proteinuria (median, 3.1g/day), hematuria (91%), and reduced estimated glomerular filtration rate (median serum creatinine, 1.9mg/dL). Hypocomplementemia was present in 31% of cases. The underlying hematologic condition for all cases was monoclonal gammopathy of renal significance (MGRS). Serum protein electrophoresis/serum immunofixation (SPEP/SIF) detected the nephropathic monoclonal immunoglobulin (MIg) in 27% of cases whereas matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) detected the nephropathic IgM in 4 of 7 tested patients. Kidney biopsy revealed membranoproliferative glomerulonephritis (83%) with nonorganized glomerular monotypic IgM (100%) and C3 deposition (96%), but C1q deposition was rare. Seventeen percent received symptomatic treatment alone, 17% received steroids alone, and 65% received other immunosuppressive therapy (mostly rituximab-based therapy). Follow-up (median, 40 months) was available for all patients. The median kidney and patient survivals were 44 and 158 months, respectively. Three patients underwent kidney transplantation, and all had recurrence, in 2 cases within a month.

LIMITATIONS

Small sample size, retrospective design, nonstandardized clinical management.

CONCLUSIONS

PGNMID-IgM mostly affects elderly men and is associated with MGRS with a low detection rate of the circulating nephropathic MIg on SPEP/SIF, which may be improved by MALDI-TOF. Kidney survival is guarded, with a high rate of early recurrence after transplant although overall survival is favorable. The pathogenesis remains unknown, but it likely involves local activation of alternative or lectin pathways of complement system by the monotypic IgM.

PLAIN-LANGUAGE SUMMARY

The IgM variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID-IgM) is very rare, and data on its clinicopathologic and outcome characteristics are scanty. This study of 23 patients with PGNMID-IgM identified in the Mayo Clinic pathology archives revealed that most patients were elderly White males who presented with proteinuria, hematuria, and reduced kidney function. The underlying hematologic condition was monoclonal gammopathy of renal significance in all cases, and the detection rate of the circulating nephropathic monoclonal immunoglobulin with serum protein electrophoresis/serum immunofixation was low but was increased using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Pathologically, all cases exhibited nonorganized glomerular monotypic IgM, most with a membranoproliferative glomerulonephritis pattern. Outcome analysis revealed a guarded kidney survival (median, 44 months), a high rate of early recurrence after transplant, and favorable patient survival (158 months).

Insights into proliferative glomerulonephritis with monoclonal immunoglobulin deposits - is it really monoclonal or not?

PURPOSE OF REVIEW

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID), is a disease defined by the presence of glomerulonephritis with nonorganized mono-isotypic immunoglobulin (Ig) deposits. This review will discuss the pathogenesis of PGNMID and address novel techniques for detection of monoclonal Ig and pathologic B-cell clones and for distinguishing monoclonal from oligoclonal Ig deposits.

RECENT FINDINGS

Because of low detection rate of circulating monoclonal Ig and nephritogenic B-cell clones and emerging reports of PGNMID-IgG in children, it has been recently argued that many PGNMID-IgG3 cases may not be monoclonal lesions. A mass spectrometry-based method, serum matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, has been shown to have superior sensitivity than immunofixation for detection of monoclonal Ig in PGNMID and other monoclonal gammopathy of renal significance (MGRS) lesions. Two novel sequencing techniques, RNA-based immunoglobulin repertoire sequencing and single-molecule real-time sequencing of monoclonal immunoglobulin, enable identification of the full-length variable sequence of monoclonal Ig, even in MGRS patients with low tumor burden and undetectable monoclonal Ig by conventional methods. Finally, staining of kidney biopsy for Ig light chain variable domain subgroups may allow for separation of true monoclonal from oligoclonal PGNMID.

SUMMARY

Novel sequencing, mass spectrometry, and immunofluorescence techniques have the potential to increase the detection rate of nephritogenic monoclonal Ig/B-cell clone and distinguish monoclonal from oligoclonal deposits in PGNMID.

Renal Pathology Society/International Kidney and Monoclonal Gammopathy Research Group consensus on pathologic definitions and terminology of monoclonal gammopathy-associated kidney lesions

The spectrum of kidney lesions associated with monoclonal gammopathy has significantly expanded over the past 2 decades, with description of new entities and variants of old entities. Pathologic diagnosis is challenging because of lesional complexity, heterogeneity, and reliance on electron microscopy and ancillary techniques. A lack of precise pathologic definitions and uniform terminology has hampered diagnostic accuracy. To address these challenges, the Renal Pathology Society and International Kidney and Monoclonal Gammopathy Research Group jointly tasked a working group of nephropathologists and nephrologists to establish consensus-based terminology and definitions for monoclonal gammopathy-associated kidney lesions. Participants included experts in the field with international representation. This report presents their recommendations. For each lesion, prerequisite (mandatory) diagnostic criteria and supportive (nonmandatory) features are proposed. New terminology is provided for some lesions. Application of standardized terminology and definitions should help harmonize kidney biopsy diagnosis with precision therapy in the monoclonal gammopathy-associated kidney disorders.

Kidney disease in multiple myeloma

Renal disease is a frequent complication of symptomatic multiple myeloma, that increases morbidity and reduces quality of life and overall survival. It may result from various lesions, the most frequent being light chain cast nephropathy (LCCN), related to precipitation of monoclonal free light chains (FLC) with uromodulin in distal tubules. Rapid identification of the type of kidney disease with appropriate management is key. LCCN typically reveals the underlying myeloma and manifests with severe acute kidney injury, high serum FLC level (>500 mg/l) and predominant light chain proteinuria (urine albumin/creatinine ratio <10 %). Urgent therapy is required, based on vigorous fluid expansion, correction of precipitating factors and introduction of efficient anti-myeloma therapy which choice should consider renal elimination of each agent and patient frailty. Early and deep reduction in serum FLC level conditions renal recovery, warranting assessment of efficacy by serial serum FLC level monitoring. In newly diagnosed patients, the combination of bortezomib, high-dose dexamethasone and an anti-CD38 monoclonal antibody is commonly used. The benefit to risk balance of quadruplets incorporating cyclophosphamide or an immunodulatory agent requires to be evaluated in prospective studies. In patients with severe acute kidney injury, reinforcing chemotherapy with FLC removal through plasma exchange or high-cutoff hemodialysis may increase the probability of renal response, despite controversial data from randomized trials. Histological assessment of the extent of cast formation and interstitial fibrosis/tubular atrophy may help evaluating renal prognosis and refining therapy. Thanks to improved overall survival, renal transplantation may be considered in selected candidates with end-stage kidney disease.

Structural profile and diversity of immunoglobulin genes in the Arctic Fox

Immunoglobulins are important components of humoral immunity and play a crucial role in protecting the body from external antigens. The Arctic fox is an important member of furbearer farming, but due to the lack of research on the immune system of the Arctic fox, animal welfare regarding Arctic fox farming has still not received enough attention. In this study, we used the Arctic fox as a research subject, described the gene locus structure of the Arctic fox immunoglobulin germline by genome comparison, and analysed the mechanism of expression diversity of the antibody pool of the Arctic fox by rapid amplification of cDNA 5' ends and high-throughput sequencing. The results showed that the Arctic fox IgH, Igκ and Igλ loci were located on chromosome 6, chromosome 5 and chromosome 14, respectively. The number of variable (V) genes identified were 18, 11 and 10, and the number of joining (J) were 3, 4 and 13 and six diversity (D) genes in the heavy chain, respectively. Among them, the D genes, J genes and constant region genes of the heavy chain were arranged in the middle of the two variable heavy gene clusters; Arctic fox had a strong preference for the use of V genes, D genes and J genes, which resulted in a low level of V(D)J recombination diversity; linkage diversity analyses showed that random deletion of the V and J genes and insertion of the N and P nucleotides of the immunoglobulins of the Arctic foxes had a large impact on the linkage diversity of the IgH, whereas the light chain The linkage diversity was mainly contributed by the random deletion of V and J genes, and the insertion of N and P nucleotides had a smaller effect; somatic hypermutation (SHM) analysis showed that the mutation types of SHM of the heavy and light chains of the Arctic fox had a strong bias towards G>A and A>G, and the bias exhibited by the three chains was basically the same. By analysing the structure and expression diversity analysis of the Arctic fox gene loci, this study could provide a theoretical basis for antibody design and vaccine development in the Arctic fox, and provide new insights to further improve the animal welfare level of Arctic fox farming.

Renal manifestations of MGUS

Kidney disease is a common complication of monoclonal immunoglobulin (MIg)-secreting B-cell disorders and predominantly occurs in patients who do not meet the criteria for an overt hematological disease. To distinguish this situation from monoclonal gammopathy of undetermined significance, which lacks organ damage, the term monoclonal gammopathy of renal significance (MGRS) was introduced to depict the association of a small, otherwise indolent B-cell clone, with renal disease induced by the secreted MIg. The spectrum of renal disorders in MGRS is wide, encompassing both tubular and glomerular disorders, classified according to the composition of deposits and their ultrastructural pattern of organization. Renal lesions, independent of the tumor burden, are mostly governed by the molecular characteristics of the MIg variable domain and involve either direct (deposition or precipitation) or indirect (autoantibody activity, complement activation) mechanisms. The diagnosis, often suggested by careful analysis of renal and extrarenal symptoms, almost always requires histological confirmation by a kidney biopsy with light, immunofluorescence, and electron microscopy studies. Most patients do not have a known monoclonal gammopathy at presentation. Hematologic investigations should include serum and urine protein electrophoresis and immunofixation, serum-free light chain measurements, and bone marrow studies with flow cytometry and cytogenetics to determine the nature of the pathogenic clone (most commonly plasmocytic). Early diagnosis before the development of severe chronic kidney disease and rapid achievement of deep hematological response through clone-targeted chemotherapy (currently based on proteasome inhibitor and monoclonal anti-CD38 antibody-based combinations for plasma cell clones) are the main factors influencing long-term renal and patient outcomes.

Clinicopathological Characteristics of Light and Heavy Chain Deposition Disease: A Case Series

RATIONALE & OBJECTIVE

Light and heavy chain deposition disease (LHCDD) is a rare form of monoclonal immunoglobulin (Ig) deposition disease, and limited clinical data are available characterizing this condition. Here we describe the clinicopathological characteristics and outcomes of LHCDD.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

13 patients with biopsy-proven LHCDD diagnosed between January 2008 and December 2022 at one of 2 Chinese medical centers.

FINDINGS

Among the 13 patients described, 6 were men and 7 were women, with a mean age of 52.6±8.0 years. Patients presented with hypertension (76.9%), anemia (84.6%), increased serum creatinine concentrations (84.6%; median, 1.7mg/dL), proteinuria (100%; average urine protein, 3.0g/24h), nephrotic syndrome (30.8%), and microscopic hematuria (76.9%). Serum immunofixation electrophoresis showed monoclonal Ig for 11 patients (84.6%). Serum free light chain ratios were abnormal in 11 patients (84.6%), and heavy/light chain ratios were abnormal in 9 of 10 patients (90%) with available data. Five patients were diagnosed with multiple myeloma. A histological diagnosis of nodular mesangial sclerosis was made in 10 patients (76.9%). Immunofluorescence demonstrated deposits of IgG subclass in 7 patients (γ-κ, n=4; γ-λ, n=3) and IgA in 5 patients (α-κ, n=2; α-λ, n=3). Six patients underwent IgG subclass staining (γ1, n=3; γ2, n=2; γ3, n=1). The deposits of IgD-κ were confirmed by mass spectrometry in 1 patient. Among 12 patients for whom data were available during a median of 26.5 months, 11 received chemotherapy and 1 received conservative treatment. One patient died, and disease progressed to kidney failure in 3 (25%). Among the 9 patients evaluable for hematological and kidney disease progression, 5 (56%) had a hematologic response and 1 (11%) exhibited improvement in kidney disease.

LIMITATIONS

Retrospective descriptive study, limited number of patients, urine protein electrophoresis or immunofixation electrophoresis test results missing for most patients.

CONCLUSIONS

In this case series of LHCDD, light and heavy chain deposition in kidney tissues were most frequent with monoclonal IgG1-κ. Among patients with evaluable data, more than half had a hematologic response, but a kidney response was uncommon.

Systematic review and meta-analysis of the clinical features of MGRS

BACKGROUND

It is crucial to identify patients with monoclonal gammopathy of renal significance (MGRS) from those without MGRS but with monoclonal gammopathy and concomitant kidney diseases. However, there have been few studies with large sample sizes, and their findings were inconsistent. This study aimed to conduct a meta-analysis of MGRS to describe the general characteristics of MGRS and its predictive factors.

METHODS

Cohort or case-control studies published through December 2022 and related to clinicopathological features of MGRS were retrieved from the PubMed, Cochrane Library, Web of Science, Scopus, and Embase databases. Two researchers searched for studies that met the inclusion criteria. In the univariate analysis, fixed- or random- effects models were used to obtain pooled estimates of the weighted mean difference (WMD) and odds ratio (OR) for risk factors. In the multivariate analysis, the ORs of the independent risk factors from each study were pooled after transforming the original estimates.

RESULTS

The meta-analysis included six studies. Univariate analysis showed that the following variables were statistically significant in MGRS: age (WMD = 1.78, 95%CI 0.21-3.35), hypertension (OR = 0.54, 95%CI 0.4-0.73), diabetes (OR = 0.42, 95%CI 0.29-0.59), albumin (WMD = - 0.26, 95%CI - 0.38--0.14), urinary protein level (WMD = 0.76, 95%CI 0.31-1.2), urinary protein ≥ 1.5 g/d (OR = 1.98, 95%CI 1.46-2.68), lambda-chain value (WMD = 29.02, 95%CI 16.55-41.49), abnormal free light-chain ratio (OR = 4.16, 95%CI 1.65-10.47), bone marrow puncture rate (OR = 5.11, 95% CI 1.31-19.95), and abnormal bone marrow outcome rate (OR = 9.63, 95%CI 1.98-46.88). Multivariate analysis showed urinary protein ≥ 1.5 g/d (OR = 2.80, 95%CI 1.53-5.15) and an abnormal free light-chain ratio (OR = 6.98, 95%CI 4.10-11.91) were associated with predictors of MGRS.

CONCLUSIONS

Compared with non-MGRS patients with monoclonal gammopathy and concomitant kidney diseases, patients with MGRS were older, had fewer underlying diseases, more urinary protein, more abnormal free light-chain ratio, and more abnormal bone marrow results. Urinary protein ≥ 1.5 g/d and an abnormal free light-chain ratio were independent risk factors for MGRS.

Kidney Transplantation in Multiple Myeloma and Monoclonal Gammopathy of Renal Significance

Recent advances in the treatment of plasma cell disorders (PCDs) have provided a wealth of therapy alternatives and improved overall survival tremendously. Various types of PCDs are associated with kidney injury and end-stage kidney disease in a considerable number of patients. Kidney transplantation (KTx) is the best option for renal replacement therapy in select patients in terms of both quality of life parameters and overall survival. Even with modern therapies, all PCDs carry the risk of hematologic progression, whereas histologic recurrence and graft loss are other prevailing concerns in these patients. The risk of mortality is also higher in some of these disorders compared with KTx recipients who suffer from other causes of kidney disease. Unlike solid cancers, there is no well-defined "waiting time" after hematologic remission before proceeding to KTx. Thus, clinicians are usually reluctant to recommend KTx to patients who develop end-stage kidney disease due to PCDs. This review aims to provide the current evidence on KTx outcomes in patients with monoclonal gammopathy of renal significance and multiple myeloma. Although immunoglobulin light chain amyloidosis is a monoclonal gammopathy of renal significance subtype, KTx outcomes in this group are mentioned in another chapter of this issue.

Immunofluorescence Use and Techniques in Glomerular Diseases: A Review

Background

Immunofluorescence (IF) studies play an essential role in the evaluation of medical renal biopsies. Particularly, in the study of renal glomerular diseases, where it provides fundamental data for the diagnosis, classification, and etiology of the glomerular pathologies. Diverse techniques may be used to optimize the utilization of IF studies, from variations on the test methodologies to expertise on the interpretation of the results and knowledge of potential pitfalls.

Summary

This manuscript presents a brief review on the history of IF and its utilization in kidney pathology, followed by a description of the IF methods, including the use of IF on paraffin-embedded tissue (paraffin IF), and other novel techniques. Guidelines on how to best report IF findings are reviewed, along with a description of antibodies commonly used in glomerular diseases, highlighting their distribution within the normal kidney and potential pitfalls in interpretation. Finally, the use and interpretation of IF are discussed in more detail in individual entities on a range of glomerular diseases.

Key Messages

IF is crucial for interpretation of renal biopsies and diagnosis of glomerular diseases. Knowledge of IF techniques, alternative procedures, its use and proper interpretation is essential for optimal utilization of IF in renal pathology, and this review proposes to serve as a simplified and practical guide on this topic.

Mitochondrial protein prohibitin promotes learning memory recovery in mice following intracerebral hemorrhage via CAMKII/CRMP signaling pathway

Prohibitin (PHB) is a mitochondrial inner membrane protein with neuroprotective, antioxidant, and apoptosis-reducing effects. This study aimed to explore the role of PHB in pathological symptoms, behavioral deficits, and cognitive impairment in a collagenase-IV-induced intracerebral hemorrhage (ICH) murine model. In this study, mice that received collagenase IV injection were pretreated with PHB or saline 21 days prior to modeling. The role of PHB in memory and learning ability was monitored using the Morris water maze, Y-maze, and rotarod, social, startle, and nest-building tests. The effect of PHB on depression-like symptoms was examined using the forced swimming, tail suspension, and sucrose preference tests. Subsequently, mouse samples were analyzed using immunohistochemistry, western blotting, Perls staining, Nissl staining, and gene sequencing. Results showed that collagenase IV significantly induced behavioral deficits, brain edema, cognitive impairment, and depressive symptoms. PHB overexpression effectively alleviated memory, learning, and motor deficits in mice with ICH. PHB markedly inhibited the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling-positive cells and protein levels of ionized calcium-binding adapter molecule 1, glial fibrillary acidic protein, and interleukin-1β in the perihematomal region of ICH mice. PHB overexpression also remarkably promoted production of neurologin1 (NLGL1), and upregulated levels of Ca2+-calmodulin-dependent kinase II (CaMKII) and collapsin response mediator protein-1 (CRMP1) proteins. In conclusion, PHB overexpression can effectively alleviate the neurological deficits and neurodegeneration around the hematoma region. This may play a protective role by upregulating the expression of NLGL1 and promoting expression of CaMKII and CRMP1.

KDOQI US Commentary on the 2021 KDIGO Clinical Practice Guideline for the Management of Glomerular Diseases

The KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases represents the first update to this set of recommendations since the initial set of KDIGO guideline recommendations was published in 2012. The pace of growth in our molecular understanding of glomerular disease has quickened and a number of newer immunosuppressive and targeted therapies have been introduced since the original set of guideline recommendations, making such an update necessary. Despite these updates, many areas of controversy remain. In addition, further updates since the publication of KDIGO 2021 have occurred which this guideline does not encompass. With this commentary, the KDOQI work group has generated a chapter-by-chapter companion opinion article that provides commentary specific to the implementation of the KDIGO 2021 guideline in the United States.

Crocetin Regulates Functions of Neural Stem Cells to Generate New Neurons for Cerebral Ischemia Recovery

Many neurons undergo apoptosis after ischemic stroke. In the brain, neurogenesis has the potential for neuronal replacement and can be activated by external conditions to repair the injury. Crocetin (CRO), naturally extracted from the plant saffron, acts as a neuroprotective agent for ischemic stroke. However, the underlying mechanism remains unknown. In this work, the effect of CRO on neural stem cell (NSC) behaviors and subventricular zone neurogenesis is investigated. Initially, NSCs are incubated with different concentrations of CRO to detect the cell proliferation and differentiation in vitro. Second, ischemic stroke induced rats are treated with CRO using nimodipine (NMDP) as a comparison. The behavioral functions, infarcted volume, and apoptotic Nissl bodies of rats are noticeably improved after CRO-treatment, comparable to those of NMDP. In addition, the increased regional cerebral blood flow and promoted neuronal differentiation are achieved by CRO-treatment. Brain tissue examination shows significantly increased neuronal regeneration in the focal ischemic injury area. Meanwhile, the length of neurites is prolonged, indicating that CRO could potentially promote neurite extension to enhance cell-cell communication. These findings demonstrate that CRO facilitated the neuronal differentiation of NSCs by activating subventricular zone neurogenesis in damaged cortex and striatum sites to repair ischemic stroke.

Membranoproliferative glomerulonephritis: no longer the same disease and may need very different treatment

Membranoproliferative glomerulonephritis (MPGN) is a pattern of glomerular injury that may be primary or secondary to infections, autoimmune diseases and haematological disorders. Primary C3G and IC-MPGN are rare and the prognosis is unfavourable. Based on immunofluorescence findings, MPGN has been classified into complement-mediated C3 glomerulopathy (C3G) and immune complex-mediated MPGN (IC-MPGN). However, this classification leaves a number of issues unresolved. The finding of genetic and acquired complement abnormalities in both C3G and IC-MPGN indicates that they represent a heterogeneous spectrum rather than distinct diseases. An unsupervised hierarchical clustering in a cohort of patients with primary C3G and IC-MPGN identified four distinct pathogenetic patterns, characterized by specific histologic and clinical features, and genetic and acquired complement abnormalities. These results provide the groundwork for a more accurate diagnosis and the development of targeted therapies. The drugs that are currently used, such as corticosteroids and immunosuppressants, are frequently ineffective in primary C3G and IC-MPGN. Eculizumab, an anti-C5 monoclonal antibody, has been used occasionally in single cases or small series. However, only a few patients have achieved remission. This heterogeneous response could be related to the extent of terminal complement activation, which may vary substantially from patient to patient. Several drugs that target the complement system at different levels are under investigation for C3G and IC-MPGN. However, clinical trials to test new therapeutics will be challenging and heavily influenced by the heterogeneity of these diseases. This creates the need to characterize each patient to match the specific complement abnormality with the type of intervention.

Proliferative Glomerulonephritis With Hidden Monotypic IgG3κ Deposits: A Case Report

Rare cases of immunoglobulin G (IgG)-dominant immune complex-mediated glomerulonephritis demonstrate immunoglobulin subclass restriction without light chain restriction. Some of these cases may represent proliferative glomerulonephritis with monotypic immunoglobulin deposits (PGNMID) in which monotypic immunoglobulin is obscured by coexisting polytypic immunoglobulin. However, rigorous demonstration of this possibility is lacking to date. Here, we describe a case of IgG3-restricted immune complex-mediated glomerulonephritis without light chain restriction that apparently "transformed" into IgG3κ-PGNMID in a subsequent biopsy. We demonstrate, using several ancillary techniques, including use of the newly described antibodies directed against the conformational epitope at the junctions of heavy and light chains (HLC-IF), that the first biopsy likely represents IgG3κ-PGNMID in which monotypic IgG3κ was hidden by polytypic IgM. This case underscores the need to consider PGNMID in a differential diagnosis of IgG-dominant immune complex-mediated glomerulonephritis without light chain restriction and highlights the potential utility of IgG subclass staining and HLC-IF in such cases to detect monotypic immunoglobulin that may be obscured by coexisting IgM and/or IgA deposits.

Light Chain-Only Immunotactoid Glomerulopathy: A Case Report

The monotypic variant of immunotactoid glomerulopathy (ITG), strongly associated with low-grade lymphoproliferative disorders, is characterized histologically by glomerulonephritis and microtubular deposits of monoclonal immunoglobulin G (IgG). We report a patient with high-risk κ light chain multiple myeloma who presented with acute kidney injury, hematuria, proteinuria, and hypocomplementemia. Kidney biopsy revealed immunotactoid glomerulopathy concomitant with κ light chain myeloma cast nephropathy. The glomerular microtubular deposits stained for κ light chain and C3 only. Proteomic analysis of glomeruli and atypical casts detected κ light chain constant domain and a single VL variability subgroup (IGKV3) in both glomeruli and casts (without γ, α, or μ heavy chain or λ light chain). C3, C5, C6, C7, and C9 were detected in glomeruli. No autoantibodies against alternative pathway of complement proteins were detected. Despite clone-directed chemotherapy, the patient remained on dialysis treatment. For this light chain-only variant of immunotactoid glomerulopathy, pathogenesis potentially involves activation of the alternative pathway of complement by a nephrotoxic κ light chain.

Nephritis-Associated Plasmin Receptor (NAPlr): An Essential Inducer of C3-Dominant Glomerular Injury and a Potential Key Diagnostic Biomarker of Infection-Related Glomerulonephritis (IRGN)

Nephritis-associated plasmin receptor (NAPlr) was originally isolated from the cytoplasmic fraction of group A Streptococci, and was found to be the same molecule as streptococcal glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and plasmin receptor (Plr) on the basis of nucleotide and amino acid sequence homology. Its main functions include GAPDH activity, plasmin-binding capacity, and direct activation of the complement alternative pathway (A-P). Plasmin trapped by deposited NAPlr triggers the degradation of extracellular matrix proteins, such as glomerular basement membranes and mesangial matrix, and the accumulation of macrophages and neutrophils, leading to the induction of plasmin-related endocapillary glomerular inflammation. Deposited NAPlr at glomerular endocapillary site directly activates the complement A-P, and the endocapillary release of complement-related anaphylatoxins, C3a and C5a, amplify the in situ endocapillary glomerular inflammation. Subsequently, circulating and in situ-formed immune complexes participate in the glomerular injury resulting in NAPlr-mediated glomerulonephritis. The disease framework of infection-related glomerulonephritis (IRGN) has been further expanded. GAPDH of various bacteria other than Streptococci have been found to react with anti-NAPlr antibodies and to possess plasmin-binding activities, allowing glomerular NAPlr and plasmin activity to be utilized as key biomarkers of IRGN.

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.

Recognizing the true face of noninfectious cryoglobulinemic glomerulonephritis

Cryoglobulinemia encompasses a group of diseases with circulating aberrant Igs, which can cause systemic cryoglobulinemic vasculitis, including cryoglobulinemic glomerulonephritis. The complexities of different types and changing etiologies of cryoglobulinemias determine its heterogeneous clinical manifestations and diagnostic difficulties. In this issue of Kidney International, Javaugue et al. have emphasized the diagnostic points of cryoglobulinemic glomerulonephritis and hematological disorders as the major culprits of noninfectious cryoglobulinemic glomerulonephritis in a large cohort.

The characteristics of seronegative and seropositive non-hepatitis-associated cryoglobulinemic glomerulonephritis

cryoglobulinemic glomerulonephritis (CryoGN) are not well-defined and cases with undetectable serum cryoglobulin (seronegative CryoGN) have not been investigated. Corresponding author: To resolve this, we retrospectively identified 81 patients with biopsy-proven non-hepatitis CryoGN, including 22 with seronegative CryoGN. The median age was 61 years and 76% presented with nephritic syndrome. A hematologic condition was found in 89% of patients, including monoclonal gammopathy of renal significance (65%) and symptomatic lymphoproliferative disorder (35%). In the seropositive group, 56% had type II, 29% type I, 8% type III cryoglobulin. Extrarenal manifestations, mostly of skin, were present in 64% and were significantly less common in seronegative CryoGN. Glomerular deposits by immunofluorescence were IgM dominant (84%) and polytypic (70%) in the seropositive group, whereas 52% of seronegative cases had monotypic deposits (i.e., type I cryoglobulin). Ultrastructurally, the deposits were organized in 77% of cases. Substructure appearance significantly differed according to the type of CryoGN, forming most commonly short cylindrical structures in type II and other organized substructures in type I CryoGN. Most patients were treated with clone-directed therapy. On follow up (median 33 months), 77% had partial or complete remission, 10% reached kidney failure and 14% died. Predictors of kidney failure on univariate analysis were AKIN stage 3, positive rheumatoid factor and biclonal gammopathy at diagnosis. We conclude that most CryoGN cases (types I and II) are due to hematologic condition and are associated with favorable outcome after clone-directed therapy. Seronegative CryoGN accounts for about a quarter of cases and is mostly a kidney-limited disease. Thus, further investigations are needed to unravel the pathophysiology of seronegative CryoGN.

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.

Heavy and light chains all at once: A new immunofluorescence technique to evaluate monoclonal immunoglobulin deposits

Tools to identify monoclonal Ig deposits within tissue specimens include immunofluorescence (IF) staining on frozen tissue for Ig heavy chains and light chains, pronase IF to unmask monoclonal Ig deposits not seen by IF staining on frozen tissue, and IF staining for IgG subclasses (IgG1-IgG4). In this issue of Kidney International, a novel diagnostic tool is introduced: IF staining for conformational epitopes at the junction of the Ig heavy chains and light chains. This technique has the potential to significantly enhance our ability to evaluate apparent monoclonal forms of renal 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.