Immune Complex Tubulointerstitial Nephritis Due to Autoantibodies to the Proximal Tubule Brush Border

Polyomavirus nephropathy: diagnosis, histologic features, and differentiation from acute rejection

Polyomaviruses, particularly BK virus, are ubiquitous latent infections that may reactivate with immunosuppression during kidney transplantation, resulting in polyomavirus nephropathy (PVN). The levels of viruria and viremia serve as tools for screening and making a presumptive diagnosis of PVN, respectively, while a definitive diagnosis requires a kidney biopsy. There are histologic classifications of PVN based on the extent of tubular cell viral infection, interstitial fibrosis, and interstitial inflammation. These classifications correlate to some degree with graft function and loss, aiding in determining treatment efficacy and prognostication. PVN has histologic overlap with acute cell-mediated rejection, making the differential diagnosis challenging, although there are suggestive features for these different causes of graft dysfunction. This article reviews the diagnosis, histologic findings, and classifications of PVN, and discusses how to differentiate viral nephropathy from acute rejection.

IgG4-related kidney disease: Clinicopathologic features, differential diagnosis, and mimics

IgG4-related kidney disease (IgG4-RKD) encompasses all forms of kidney disease that are part of IgG4-related disease (IgG4-RD). First recognized as IgG4-related tubulointerstitial nephritis (IgG4-TIN), and then IgG4-related membranous glomerulonephritis (IgG4-MGN), we now recognize additional patterns of interstitial nephritis, glomerular disease, and vascular disease that can be seen as part of IgG4-RKD. The clinical presentation is variable and can include acute or chronic kidney injury, proteinuria or nephrotic syndrome, mass lesion(s), and obstruction. While usually associated with other organ involvement by IgG4-RD, kidney-alone involvement is present in approximately 20 % of IgG4-RKD. Compared to IgG4-RD overall, patients with IgG4-RKD are more likely to show increased serum IgG4 or IgG, and more likely to have hypocomplementemia. In this review, we extensively cover other types of autoimmune and plasma cell-rich interstitial nephritis, mass forming inflammatory diseases of the kidney, and other mimics of IgG4-TIN, in particular ANCA-associated disease.

Tubular basement membrane deposits after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Extraglomerular immune complex deposition is rare and only a few membranous nephropathy cases with tubular basement membrane deposits have been reported following allogeneic hematopoietic stem cell transplantation.

CASE PRESENTATION

We reported a 56-year-old man with increased serum creatinine after allogeneic hematopoietic stem cell transplantation who underwent a renal biopsy. Tubular interstitial nephritis was identified on light microscope. The unique histologic features were diffuse tubular basement membrane immune complex deposition detected by both immunofluorescence and electron microscopy, while the glomerular involvement was inconspicuous. The differential diagnosis from other forms of tubular basement membrane deposition is discussed.

CONCLUSION

Diffuse granular tubular basement membrane immune complex deposition with minimal glomerular involvement is also a manifestation of renal complication in hematopoietic stem cell transplantation recipient. However, the exact mechanism and target antigen remains unknown.

Hypomagnesemia, Hypocalcemia, and Tubulointerstitial Nephropathy Caused by Claudin-16 Autoantibodies

BACKGROUND

Chronic hypomagnesemia is commonly due to diarrhea, alcoholism, and drugs. More rarely, it is caused by genetic defects in the effectors of renal magnesium reabsorption.

METHODS

In an adult patient with acquired severe hypomagnesemia, hypocalcemia, tubulointerstitial nephropathy, and rapidly progressing kidney injury, similarities between the patient's presentation and features of genetic disorders of renal magnesium transport prompted us to investigate whether the patient had an acquired autoimmune cause of renal magnesium wasting. To determine if the patient's condition might be explained by autoantibodies directed against claudin-16 or claudin-19, transmembrane paracellular proteins involved in renal magnesium absorption, we conducted experiments with claudin knockout mice and transfected mouse kidney cells expressing human claudin-16 or claudin-19. We also examined effects on renal magnesium handling in rats given intravenous injections of IgG purified from sera from the patient or controls.

RESULTS

Experiments with the knockout mice and in vitro transfected cells demonstrated that hypomagnesemia in the patient was causally linked to autoantibodies directed against claudin-16, which controls paracellular magnesium reabsorption in the thick ascending limb of Henle's loop. Intravenous injection of IgG purified from the patient's serum induced a marked urinary waste of magnesium in rats. Immunosuppressive treatment combining plasma exchange and rituximab was associated with improvement in the patient's GFR, but hypomagnesemia persisted. The patient was subsequently diagnosed with a renal carcinoma that expressed a high level of claudin-16 mRNA.

CONCLUSIONS

Pathogenic claudin-16 autoantibodies represent a novel autoimmune cause of specific renal tubular transport disturbances and tubulointerstitial nephropathy. Screening for autoantibodies targeting claudin-16, and potentially other magnesium transporters or channels in the kidney, may be warranted in patients with acquired unexplained hypomagnesemia.

Antibrush Border Antibody Disease: A Case Report and Literature Review

Anti-brush border antibody (ABBA) disease, also called anti-low-density lipoprotein receptor-related protein 2 (anti-LRP2) nephropathy, occurs due to the formation of antibodies against brush border antigens of the renal proximal convoluted tubule. We report a case of ABBA disease in a male farmer in his 30s who presented with 2 years of polyuria, dysuria, nocturia, and urinary urgency. He described a history of long-term occupational exposure to pesticides and silica, evolving into possible pneumoconiosis, and prior pulmonary tuberculosis. At presentation, he had reduced kidney function (serum creatinine 3.6 mg/dL) with hyponatremia, hypokalemia, hypophosphatemia, a normal anion gap, metabolic acidosis, and respiratory acidosis, and 2.2 g/day of urine proteinuria. The kidney biopsy was consistent with ABBA, showing amorphous immune-deposits in the tubular basement membrane and strong positivity on indirect immunofluorescence in the brush border of the proximal tubules. The trigger for production of ABBA is still unknown, but it may be associated with chronic conditions such as pulmonary tuberculosis and occupational exposures such as silica and pesticides, as seen in the patient in this report. Most cases do not respond to immunosuppression, and the prognosis is poor.

Anti-LDL Receptor-Related Protein 2 Nephropathy with Synchronous Primary Kidney Extranodal Marginal Zone Lymphoma

Introduction

Anti-LDL receptor-related protein 2 (anti-LRP2) nephropathy is a rare but progressive form of autoimmune-mediated tubulointerstitial nephritis and glomerular disease, characterized by a classic pattern of immune complex deposition in the kidney. A theoretic link between autoimmune disease and lymphoproliferative diseases exists, and therefore, in some cases autoimmune-mediated inflammation and lymphoproliferative neoplasm can co-exist in the same site.

Case Presentation

An elderly man presented with 6 months of weight loss and fatigue. Subsequent workup showed an elevated serum creatinine and subnephrotic range proteinuria. Kidney biopsy was performed which revealed anti-LRP2 nephropathy with concurrent primary kidney extranodal marginal zone lymphoma. He was subsequently treated with rituximab but remains dialysis-dependent (12 months after his initial diagnosis, at time of publication of this report).

Conclusion

We discuss the bidirectional relationship between autoimmune disease and lymphoma in the kidney, along with a brief review of the literature pertaining to these rare lesions. Our case report highlights the diagnostic difficulties faced by pathologists when encountering this entity. We also attempt to spread awareness about the co-existence of tubulointerstitial inflammation and lymphoproliferative disorder, which may be under-recognized.

Prevalence of autoantibodies that bind to kidney tissues in cats and association risk with antibodies to feline viral rhinotracheitis, calicivirus, and panleukopenia

BACKGROUND

The feline viral rhinotracheitis, calicivirus, and panleukopenia (FVRCP) vaccine, prepared from viruses grown in the Crandell-Rees feline kidney cell line, can induce antibodies to cross-react with feline kidney tissues.

OBJECTIVES

This study surveyed the prevalence of autoantibodies to feline kidney tissues and their association with the frequency of FVRCP vaccination.

METHODS

Serum samples and kidneys were collected from 156 live and 26 cadaveric cats. Antibodies that bind to kidney tissues and antibodies to the FVRCP antigen were determined by enzyme-linked immunosorbent assay (ELISA), and kidney-bound antibody patterns were investigated by examining immunofluorescence. Proteins recognized by antibodies were identified by Western blot analysis.

RESULTS

The prevalences of autoantibodies that bind to kidney tissues in cats were 41% and 13% by ELISA and immunofluorescence, respectively. Kidney-bound antibodies were observed at interstitial cells, apical border, and cytoplasm of proximal and distal tubules; the antibodies were bound to proteins with molecular weights of 40, 47, 38, and 20 kDa. There was no direct link between vaccination and anti-kidney antibodies, but positive antibodies to kidney tissues were significantly associated with the anti-FVRCP antibody. The odds ratio or association in finding the autoantibody in cats with the antibody to FVRCP was 2.8 times higher than that in cats without the antibody to FVRCP.

CONCLUSIONS

These preliminary results demonstrate an association between anti-FVRCP and anti-cat kidney tissues. However, an increase in the risk of inducing kidney-bound antibodies by repeat vaccinations could not be shown directly. It will be interesting to expand the sample size and follow-up on whether these autoantibodies can lead to kidney function impairment.

Complete remission of nephrotic syndrome in a young woman with anti-LRP2 nephropathy after immunosuppressive therapy

BACKGROUND

Anti-low density lipoprotein receptor-related protein 2 (LRP2) nephropathy/anti-brush border antibody (ABBA) disease is a disorder characterized by acute tubulointerstitial injury associated with circulating antibodies to kidney proximal tubular brush border protein LRP2/megalin. Patients are typically elderly and present with acute kidney injury and subnephrotic proteinuria. They progress to end-stage renal disease with poor response to immunosuppressive therapies.

CASE PRESENTATION

We report a case of a 29-year-old Chinese woman, who presented with nephrotic syndrome with normal kidney function. Kidney biopsy showed no obvious tubular injury or interstitial inflammation. Positive immunoglobulin G (IgG) staining was revealed along the brush border of proximal tubular cells. Anti-LRP2 antibody was identified in serum, consistent with a diagnosis of anti-LRP2 nephropathy. The patient achieved complete remission after receiving prednisone and cyclophosphamide.

CONCLUSIONS

Anti-LRP2 nephropathy can also present as nephrotic syndrome in young patients and complete remission from nephrotic syndrome may be achieved after immunosuppressive therapy.

Megalin/lipoprotein receptor-related protein 2 autoimmunity and kidney disease

In this issue of Clinical Kidney Journal, Gamayo et al. describe two cases of anti-low-density lipoprotein receptor-related protein 2 (LRP2) nephropathy. This is a recently described entity that has features of both tubulointerstitial disease and segmental membranous nephropathy. The originality of the present report consists of the association of a disease thought to be rare (only 13 in prior described patients, 11 in the past year) with B-cell lymphoproliferative disease. Together with the finding of a third case among 224 elderly patients studied, this raises the issue of the underdiagnoses of LRP2 nephropathy, on top of the potential association to B-cell malignancy. We now put these findings in context within the wider frame of autoimmunity against megalin/LRP2 and related antigens such as Fx1A and CD69.

A case of immune complex mediated tubulointerstitial disease and nephrotic syndrome: anti LRP-2 Nephropathy with diffuse podocyte effacement

Anti-LDL Receptor-Related Protein 2 (Anti-LRP2) nephropathy is a rare form of kidney disease that affects the older patients and is characterized with acute kidney injury (AKI) and progressive renal tubular injury associated with IgG immune complex deposits along the basement membrane of proximal tubules, and circulating autoantibodies to the proximal tubule brush border protein LRP2 (megalin). We present the case of a 79-year-old man who was hospitalized for worsening malaise, abdominal distention and bilateral lower extremity edema, diagnosed with AKI and had nephrotic range proteinuria. Percutaneous kidney biopsy revealed tubulointerstitial nephritis with IgG immune complex deposits along the basement membrane of proximal tubules and brush borders. Immunofluorescence staining for LRP2 (megalin) showed similar granular tubular basement membrane deposits along the proximal tubules and proximal tubule brush borders. Electron microscopy revealed global podocyte foot process effacement. The patient was started on oral prednisolone 1 mg/kg and rituximab at a dose of 375 mg/m² once weekly for 4 weeks with gradual tapering of prednisone. This case with AKI and nephrotic syndrome highlights the significant morphologic overlap with minimal change disease and anti-LRP2 nephropathy, which is associated with autoantibodies to the tubular brush border protein LRP2/megalin.

Production of polyclonal antibody against kidney antigens: a model for studying autoantibody in feline chronic kidney diseases

Chronic kidney disease is considered to be most common in geriatric domestic cats. It has been reported that the feline viral rhinotracheitis, calicivirus, and panleukopenia (FVRCP) vaccine prepared from the Crandell-Rees feline kidney (CRFK) cell line can induce cross-reactions of antibodies with feline kidney tissues. As an anti-cat kidney antibody was not available commercially for this study of autoantibody in cats, the purpose of this study was to produce anti-cat kidney antibody in rabbits for further study of autoantibody in cats after FVRCP vaccination. Kidney proteins from cadaveric cats were extracted and immunized into rabbits using Montanide as the adjuvant. Based on enzyme-linked immunosorbent assay measurement, all immunized rabbits produced high levels of anti-cat kidney antibodies and some began to produce antibodies as early as 2 weeks after immunization. Immunofluorescence staining of rabbit sera showed kidney-bound antibodies in glomerulus, Bowman's capsule, apical surface of the proximal convoluted tubule, peritubular surface, and interstitial cells. Western blot analysis of cat kidney proteins revealed molecular weights (M.W.) of 72, 55, 47, and 31 kDa, while binding to the CRFK cell proteins was observed at M.W. of 43 and 26 kDa. The antibody that recognized the 47 kDa protein was similarly detected in cats with autoantibody presence after FVRCP vaccination. The kidney-bound antibody profile at different time points and its patterns in rabbits could be used as a model for the study of autoantibody to cat kidney in feline chronic kidney diseases.

Anti-LRP2 nephropathy with concurrent kidney infiltration by lymphoma

Anti-low-density lipoprotein receptor-related lipoprotein 2 (LRP2) nephropathy/anti-brush border antibody disease is rare and characterized by tubular basement membrane, Bowman’s capsule and glomerular subepithelial immune deposits on kidney biopsy. No reported cases have occurred in patients with lymphoproliferative disorders or monoclonal gammopathies. We present two cases of anti-LRP2 nephropathy that occurred in patients with progressive low-grade B-cell lymphoma and had concurrent kidney infiltration by lymphoma on biopsy. We speculate that underlying immune dysregulation related to lymphoma may contribute to the development of this rare autoimmune kidney disease in some patients.

Anti-LRP2 Nephropathy With Abundant IgG4-Positive Plasma Cells: A Case Report

In older adults, the most common kidney biopsy diagnoses include pauci-immune crescentic glomerulonephritis, membranous nephropathy, and focal segmental glomerulosclerosis. Recently, investigators described a small series of older patients (aged 66-80 years) with acute kidney injury and a kidney biopsy demonstrating tubular basement membrane (TBM) immune deposits of polytypic immunoglobulin G (IgG) and C3, acute tubular injury, and tubulointerstitial inflammation. They identified a circulating antibody against kidney tubular low-density lipoprotein (LDL) receptor-related protein 2 (LRP2; also known as megalin) in patients' sera and colocalization of LRP2 with IgG in TBM deposits. We present a rare case of anti-LRP2 nephropathy/anti-brush border antibody disease and describe the novel feature of abundant IgG4-positive interstitial plasma cells. Along with the combination of TBM deposits, tubulointerstitial nephritis (TIN), and segmental glomerular subepithelial immune deposits seen in both entities, this newly described feature adds to the morphologic overlap with IgG4-related TIN. Identification of large TBM deposits using light microscopy and IgG staining of apical aspects of proximal tubules using immunofluorescence microscopy can point to the correct diagnosis of anti-LRP2 nephropathy and prompt confirmatory studies. Particularly in older patients with immune complex-mediated TIN who lack clinical, laboratory, radiographic, and/or characteristic histologic features of IgG4-TIN or other autoimmune, infectious, or drug-related injury, a diagnosis of anti-LRP2 nephropathy should be considered.

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. All but one of the patients also had segmental glomerular deposits on renal biopsy specimen. Patients with ABBA disease were elderly and presented with AKI and subnephrotic proteinuria. Serum from all patients but not controls recognized a high molecular weight protein in renal tubular protein extracts that we identified as LDL receptor-related protein 2 (LRP2), also known as megalin, by immunoprecipitation and mass spectrometry. Immunostaining revealed that LRP2 specifically colocalized with IgG in the tubular immune deposits on the ABBA biopsy specimen but not the control specimen analyzed. Finally, ABBA serum samples but not control samples showed reactivity against recombinantly expressed N-terminal LRP2 fragments on Western blots and immunoprecipitated the recombinantly expressed N-terminal region of LRP2. This case series details the clinicopathologic findings of patients with ABBA disease and shows that the antigenic target of these autoantibodies is LRP2. Future studies are needed to determine the disease prevalence, stimulus for ABBA, and optimal treatment.

Autoantibodies Targeting a Collecting Duct-Specific Water Channel in Tubulointerstitial Nephritis

Tubulointerstitial nephritis is a common cause of kidney failure and may have diverse etiologies. This form of nephritis is sometimes associated with autoimmune disease, but the role of autoimmune mechanisms in disease development is not well understood. Here, we present the cases of three patients with autoimmune polyendocrine syndrome type 1 who developed tubulointerstitial nephritis and ESRD in association with autoantibodies against kidney collecting duct cells. One of the patients developed autoantibodies targeting the collecting duct-specific water channel aquaporin 2, whereas autoantibodies of the two other patients reacted against the HOXB7 or NFAT5 transcription factors, which regulate the aquaporin 2 promoter. Our findings suggest that tubulointerstitial nephritis developed in these patients as a result of an autoimmune insult on the kidney collecting duct cells.