Clinicopathological characteristics of patients with IgG4-related tubulointerstitial nephritis

Immunoglobulin G4-Related Kidney Disease: A Comprehensive Pictorial Review of the Imaging Spectrum, Mimickers, and Clinicopathological Characteristics

Immunoglobulin G4 (IgG4)-related kidney disease (IgG4-KD) has recently been demonstrated to be an important part of IgG4-related sclerosing disease (IgG4-SD). However, since IgG4-KD is still relatively unfamiliar to radiologists and physicians as compared to IgG4-SD involving other organs, it could, therefore, be easily missed. In this article, we present a comprehensive pictorial review of IgG4-KD with regards to the imaging spectrum, mimickers, and clinicopathologic characteristics, based on our clinical experience with 48 patients during the past 13 years, as well as a literature review. Awareness of the broad imaging spectrum of IgG4-KD and differential diagnosis from its mimickers will thus facilitate its early diagnosis and treatment.

Lesson of the month 2: IgG4-related renal mass with spontaneous resolution

Immunoglobulin G4-related disease (IgG4-RD) is a systemic inflammatory condition that may involve any organ in the body, including the kidneys. However, renal parenchymal lesions are not seen frequently and the treatment strategy remains unclear. We describe a case of IgG4-related renal mass, which resolved spontaneously. The patient presented with right loin pain, constitutional symptoms and raised inflammatory markers. Magnetic resonance imaging (MRI) showed a large infiltrative mass centered on the right renal hilum and biopsy demonstrated histological changes in keeping with IgG4-RD. A careful 'watch-and-wait' approach was taken and at six months following initial presentation, the patient's symptoms had fully resolved and inflammatory markers had normalised. Repeat MRI showed almost complete resolution of the mass. We propose that a careful 'watch-and-wait' approach could be considered as an alternative to immune suppression for IgG4-related renal masses, especially if they are not causing symptoms or organ compromise.

Clinicopathological characteristics of immunoglobulin G4-related sialadenitis

Introduction

Immunoglobulin G4-related disease (IgG4-RD) is a newly recognized fibro-inflammatory condition. Forty-two cases with immunoglobulin G4-related sialadenitis (IgG4-RS) confirmed by histopathological and immunohistochemical assessment were studied to clarify the clinicopathologic characteristics of the salivary glands involved in IgG4-RS, especially the relationship between the histopathologic features and function of salivary glands or serum levels of IgG4.

Methods

Clinical, serologic, imaging and histopathological data of these cases were analyzed. CT volumes of submandibular, parotid, and lacrimal glands were calculated. The saliva flow rate was measured. Scintigraphy with 99mTc-pertechnetate was undertaken in 31 cases, and the concentration index (CI) and secretion index (SI) was calculated. Relationships between fibrosis severity and salivary gland function or serum IgG4 levels were analyzed.

Results

The first symptom was swelling of bilateral submandibular or lacrimal glands. Physical examination showed multiple bilateral major salivary glands (including sublingual and accessory parotid glands) and lacrimal glands were enlarged in IgG4 RS. Multiple enlarged cervical lymph nodes were noted in 30 patients. Saliva flow at rest was lower than normal in 34 cases; stimulated saliva flow was lower than normal in 15 cases. Secretory function was reduced more severely in the submandibular glands than in the parotid glands. Serum levels of IgG4 were elevated in 95.2% of cases and 78.6% patients had increased IgE levels. Serum IgG4 level was higher and saliva secretion lower as glandular fibrosis increased.

Conclusions

Prominent changes in the morphology, histology, immunohistochemistry and secretion of the major salivary glands of IgG4-RS patients were accompanied by involvement of the lacrimal glands and cervical lymph nodes. Elevated IgE, allergic history, eosinophil infiltration suggest allergic reactions as a potential pathogenesis of IgG4-RS. Severity of glandular fibrosis correlated with salivary function and serum levels of IgG4.

Evaluation of diagnostic criteria for IgG4-related tubulointerstitial nephritis

Background

IgG4-TIN is the most common pattern of renal involvement in IgG4-related disease. There are several proposed diagnostic criteria of IgG4-TIN recently. Two of them proposed by the Mayo Clinic and JSN are predominant. However, histopathological criteria of the number of IgG4+ plasma cells and several histological features are still under discussion due to low amount of tissue in renal biopsy specimens and low frequency of this kind of specimens. We aimed to screen IgG4-TIN on archived renal biopsy samples and evaluated the application of two proposed diagnostic criteria.

Methods

We selected 480 interstitial inflammation samples for light and electron microscopy and immunohistochemistry of CD138, IgG and IgG4 test. The Mayo Clinic proposed criteria diagnosed high-probability IgG4-TIN and JSN criteria confirmed IgG4-TIN.

Results

Twelve high-probability IgG4-TIN were screened by histology, imaging, serology and other organ involvement according to the Mayo Clinic proposed criteria. The previous principal pathological diagnoses were IgAN (n=4), CreGN (n=4), tubulointerstitial nephritis (n=3) and LN (n=1). Three cases showed storiform fibrosis and a bird’s eye pattern. The distribution of IgG4+ plasma cells was focal, multifocal or diffuse, with a mixed mild, moderate or strong stainingpattern. Their treatment and clinical outcomes varied depending on different levels of proteinuria, serum creatinine, eGFR and original glomerular disease presentation. Therefore, we applied strict histological criteria of storiform fibrosis and evenly distributed IgG4+ plasma cells by JSN to confirm typical IgG4-TIN. Two cases were finally diagnosed as real IgG4-TIN. One was previously diagnosed as idiopathic interstitial nephritis with rapid response to corticosteroid therapy. The other was CreGN with immune complex deposits, which had poor outcome and long-term hemodialysis.

Conclusions

IgG4-TIN might present concurrently with glomerular disease. The proposed criteria by the Mayo Clinic is flexible, sensitive, and superior in the identification of early-stage or atypical IgG4-TIN, with enhanced risk of misdiagnosis as compared to the proposed criteria by JSN, which is stricter, more specific, and might overlook early-stage or atypical IgG4-TIN. We propose a new set of criteria to improve pathologist-derived diagnosis.

Prohibitin Is Involved in Patients with IgG4 Related Disease

Objective

IgG4-related disease (IgG4-RD) is a chronic systemic disease involved in many organs and tissues. As only limited autoantigens have been found since the beginning of this century, the aim of this study was to reveal new candidate autoantigens of IgG4-RD.

Methods

Multiple cell lines including HT-29, EA.hy926, HEK 293 and HepG2 were used to test the binding ability of circulating autoantibodies from IgG4-RD sera. The amino-acid sequence was then analyzed by matrix-assisted laser desorption/ionization time-of-flight tandem (MALDI-TOF/TOF) mass spectrometry. After the cloning and expression of recombinant putative autoantigen in a bacterial expression system, the corresponding immuno assay was set up and utilized to observe the prevalence of serum autoantibodies in a large set of confirmed clinical samples.

Results

One positive autoantigen was identified as prohibitin. ELISA analysis showed that a majority of patients with IgG4-RD have antibodies against prohibitin. Anti-prohibitin antibodies were present in the sera of patients with definite autoimmune pancreatitis (25/34; 73.5%), Mikulicz’s disease (8/15; 53.3%), retroperitoneal fibrosis (6/11; 54.5%), other probable IgG4-RD (26/29; 89.7%) and Sjögren’s syndrome (4/30; 13.3%) but not in apparently healthy donors (1/70; 1.4%).

Conclusions

An association between prohibitin and patients with some IgG4-RD was observed, although the results were quite heterogeneous among different individuals within autoimmune pancreatitis, Mikulicz’s disease and retroperitoneal fibrosis.

IgG4-related disease

IgG4-related disease is a protean condition that mimics many malignant, infectious, and inflammatory disorders. This multi-organ immune-mediated condition links many disorders previously regarded as isolated, single-organ diseases without any known underlying systemic condition. It was recognised as a unified entity only 10 years ago. Histopathology is the key to diagnosis. The three central pathology features of IgG4-related disease are lymphoplasmacytic infiltration, storiform fibrosis, and obliterative phlebitis. The extent of fibrosis is an important determinant of responsiveness to immunosuppressive therapies. IgG4-related disease generally responds to glucocorticoids in its inflammatory stage, but recurrent or refractory cases are common. Important mechanistic insights have been derived from studies of patients treated by B-cell depletion. Greater awareness of this disease is needed to ensure earlier diagnoses, which can prevent severe organ damage, disabling tissue fibrosis, and even death. Identification of specific antigens and T-cell clones that drive the disease will be the first steps to elucidate the pathogenesis of IgG4-related disease.

Distinct cytokine mRNA expression pattern in immunoglobulin G4-related kidney disease associated with renal cell carcinoma

We treated a 61-year-old man with immunoglobulin (Ig)G4-related kidney disease (IgG4-RKD). He had a history of allergic diseases and an allergic reaction and had received a diagnosis of autoimmune pancreatitis (AIP). He had also received a diagnosis of renal cell carcinoma (RCC) and had undergone segmental resection of the left kidney at 59 years of age. His serum amylase level and number of peripheral eosinophils increased after RCC development. We hypothesized that the RCC may have induced AIP and IgG4-RKD and we therefore examined the excised RCC tissue; typical findings of IgG4-RKD associated with RCC were recognized. We next evaluated the mRNA expression of cytokines in the excised tissues of this case and ten other ordinary RCC cases. In all cases, notable levels of IL-10 mRNA and high levels of TGF-β mRNA were seen. Although prominent differences were not observed in the mRNA expression of Th1, Th17 and Treg cytokines in all cases, the present case alone showed increased production of the Th2 cytokines IL-4 and IL-5, which were not detected in ordinary RCC cases. Although the mechanism underlying IgG4-RKD development has not yet been determined, Th2 and Treg cells are thought to play a prominent role in the pathogenesis. It is therefore likely that in this case, the association of these two diseases was not coincidental, and a distinct immune response against RCC may trigger IgG4-RKD development.

Immunoglobulin G4-related tubulointerstitial nephritis associated with interstitial pulmonary disease: Report of a case with review of literature

Immunoglobulin G4-related disease (IgG4-RD) is an emerging clinicopathological entity. Renal involvement is dominated by tubulointerstitial nephritis (TIN) with IgG4-positive plasma cells and fibrosis. IgG4-RD commonly affects middle-aged to elderly men with accompanying extra-renal lesions such as sialadenitis, lymphadenopathy, or type 1 autoimmune pancreatitis, all of which respond favorably to corticosteroid therapy. The disease burden of IgG4-related kidney disease (IgG4-RKD) in India remains largely underestimated. We report a case of IgG4-RKD manifesting as TIN associated with interstitial pulmonary disease, illustrating typical clinico-pathologic, serologic, immuno-histochemical, and ultrastructural features of this condition. In view of potential amelioration of renal dysfunction with appropriate therapy, the need for awareness of this condition and early diagnosis is highlighted.

Mitochondrial-dependent Autoimmunity in Membranous Nephropathy of IgG4-related Disease

The pathophysiology of glomerular lesions of membranous nephropathy (MN), including seldom-reported IgG4-related disease, is still elusive. Unlike in idiopathic MN where IgG4 prevails, in this patient IgG3 was predominant in glomerular deposits in the absence of circulating anti-phospholipase A₂ receptor antibodies, suggesting a distinct pathologic process. Here we documented that IgG4 retrieved from the serum of our propositus reacted against carbonic anhydrase II (CAII) at the podocyte surface. In patient's biopsy, glomerular CAII staining increased and co-localized with subepithelial IgG4 deposits along the capillary walls. Patient's IgG4 caused a drop in cell pH followed by mitochondrial dysfunction, excessive ROS production and cytoskeletal reorganization in cultured podocytes. These events promoted mitochondrial superoxide-dismutase-2 (SOD2) externalization on the plasma membrane, becoming recognizable by complement-binding IgG3 anti-SOD2. Among patients with IgG4-related disease only sera of those with IgG4 anti-CAII antibodies caused low intracellular pH and mitochondrial alterations underlying SOD2 externalization. Circulating IgG4 anti-CAII can cause podocyte injury through processes of intracellular acidification, mitochondrial oxidative stress and neoantigen induction in patients with IgG4 related disease. The onset of MN in a subset of patients could be due to IgG4 antibodies recognizing CAII with consequent exposure of mitochondrial neoantigen in the context of multifactorial pathogenesis of disease.

•

In a patient with IgG4-related disease, glomerular CAII increases and colocalizes with IgG4 deposits.

•

IgG4 from patient's serum reacts against CAII expressed by podocytes.

•

IgG4 causes acidification, mitochondrial dysfunction and ROS-dependent cytoskeletal alterations in cultured podocytes.

•

IgG4 induces the externalization on the plasma membrane of clustered SOD2, becoming recognizable by complement-binding IgG3.

IgG4-related autoimmune diseases: Polymorphous presentation complicates diagnosis and treatment

BACKGROUND

IgG4-associated autoimmune diseases are systemic diseases affecting multiple organs of the body. Autoimmune pancreatitis, with a prevalence of 2.2 per 100,000 people, is one such disease. Because these multi-organ diseases present in highly variable ways, they were long thought just to affect individual organ systems. This only underscores the importance of familiarity with these diseases for routine clinical practice.

METHODS

This review is based on pertinent articles retrieved by a selective search in PubMed, and on the published conclusions of international consensus conferences.

RESULTS

The current scientific understanding of this group of diseases is based largely on case reports and small case series; there have not been any randomized controlled trials (RCTs) to date. Any organ system can be affected, including (for example) the biliary pathways, salivary glands, kidneys, lymph nodes, thyroid gland, and blood vessels. Macroscopically, these diseases cause diffuse organ swelling and the formation of pseudotumorous masses. Histopathologically, they are characterized by a lymphoplasmacytic infiltrate with IgG4-positive plasma cells, which leads via an autoimmune mechanism to the typical histologic findings--storiform fibrosis ("storiform" = whorled, like a straw mat) and obliterative, i.e., vessel-occluding, phlebitis. A mixed Th1 and Th2 immune response seems to play an important role in pathogenesis, while the role of IgG4 antibodies, which are not pathogenic in themselves, is still unclear. Glucocorticoid treatment leads to remission in 98% of cases and is usually continued for 12 months as maintenance therapy. Most patients undergo remission even if untreated. Steroid-resistant disease can be treated with immune modulators.

CONCLUSION

IgG4-associated autoimmune diseases are becoming more common, but adequate, systematically obtained data are now available only from certain Asian countries. Interdisciplinary collaboration is a prerequisite to proper diagnosis and treatment. Treatment algorithms and RCTs are needed to point the way to organ-specific treatment in the future.

Immunohistological analysis for immunological response and mechanism of interstitial fibrosis in IgG4-related kidney disease

OBJECTIVES

Our study aimed to clarify the immunological characteristics and the mechanism of interstitial fibrosis in immunoglobulin G4-related kidney disease (IgG4-RKD) by the immunohistological analysis.

METHODS

Immunohistological study was performed in the biopsied renal tissues of 16 IgG4-RKD, 16 Sjögren syndrome (SJS), and 17 idiopathic tubulointerstitial nephritis (ITIN) patients using antibodies against IgG; IgG1; IgG4; CD38; CD3; C-X-C chemokine receptor type 3 (CXCR3); chemokine (C-C motif) receptor 4 (CCR4); forkhead box 3 (Foxp3); Type I, Type III, Type IV, and Type VI collagens; and transforming growth factor (TGF)-β1.

RESULTS

Interstitial lymphoplasmacytic and eosinophilic infiltration and the severity of interstitial fibrosis were greater in IgG4-RKD than SJS and ITIN. The ratio of CXCR3+/CD3 + cells was greater in SJS as compared with that in IgG4-RKD and ITIN. The ratio of CCR4+/CD3 + cells was not different among the three diseases. The ratio of interstitial IgG4+/IgG+ plasma cells, Foxp3+/CD3 + cells, and TGF-β1 + cells/total infiltrating cells was higher in IgG4-RKD than SJS and ITIN. There was a positive correlation between the ratio of Foxp3+/CD3 + cells and that of IgG4+/IgG+ plasma cells in IgG4-RKD. Significant correlation was found between the ratio of Foxp3+/CD3 + cells and that of TGF-β1 + cells/total infiltrating cells in IgG4-RKD. Foxp3 + cells and TGF-β1 + cells were colocalized in the interstitium in IgG4-RKD. The significant correlation between the ratio of TGF-β1 + cells/total infiltrating cells and the severity of fibrosis was noticed in IgG4-RKD. The interstitial distribution of type III collagen and type IV collagen was higher in IgG4-RKD than in SJS.

CONCLUSIONS

Our results suggest that regulatory T-cells (Tregs) may play a central role in IgG4 production in the interstitium and TGF-β1 induced by Tregs may play a pivotal role in the interstitial fibrosis including type III and type IV collagens in IgG4-RKD.

[IgG4-related disease treatment in 2014: Update and literature review]

IgG4-related disease is an inflammatory disorder characterized by a polyclonal lymphoplasmacytic tissue infiltrate, with numerous IgG4+ plasmocytes, evolving toward fibrosis. The disease is heterogeneous and affects several tissues and organs synchroneously or metachroneously. Both the fibrosis and the tumor forming characteristics of the disease can be responsible of irreversible tissue damage. For these reasons treatment is usually necessary. A dramatic response is usually observed with steroid treatment but relapses are frequent. Immunosuppressive agents and rituximab are used as second line treatments. We review here previous studies on treatment and suggest general recommendations for the treatment and follow up of patients with IgG4-related disease.

A case of IgG4-positive plasma cell-rich tubulointerstitial nephritis in a kidney allograft mimicking IgG4-related kidney disease

A 51-year-old woman received an ABO blood type-incompatible renal transplant. She was administered rituximab and basiliximab and underwent plasma exchanges for induction therapy, followed by administration of tacrolimus, mycophenolate mofetil and methylprednisolone as maintenance immunosupression therapy. A planned renal biopsy 2 years after transplantation revealed infiltration of plasma cells in the renal interstitium, although there was no 'storiform' fibrosis surrounding these cells. There were also no findings of rejection, BK virus nephropathy, or atypical plasma cells. Immunohistochemical stainings showed a large number of IgG4-positive plasma cells, most of which expressed kappa-type light chains. A CT scan showed a mass at the renal hilum. The serum IgG4 level was high. Based on these findings, the patient was suspected of having IgG4-related kidney disease. Nine months after the biopsy, her serum creatinine level increase to 1.56 mg/dL and the dose of methylprednisolone was therefore increased to 16 mg/day. Three months after this increase in steroid, a CT scan showed the hilum mass had disappeared. A follow-up biopsy 5 months later showed that infiltration of plasma cells in the renal interstitium had decreased markedly, although focal and segmental severely fibrotic lesions with IgG4-positive plasma cells were observed. Serum IgG4 levels decreased immediately after the increase in steroid dose and remained <100 mg/dL despite a reduction in methylprednisolone to 6 mg/day. Serum creatinine levels also remained stable at around 1.6 mg/dL. To our knowledge, this is the first report of IgG4-positive plasma cell-rich tubulointerstitial nephritis mimicking IgG4-related kidney disease after kidney transplantation.

IgG4-related Kidney Disease in Which the Urinalysis, Kidney Function and Imaging Findings Were Normal

IgG4-related kidney disease (IgG4RKD) is recognized as a fibroinflammatory disease characterized by storiform fibrosis, lymphoplasmacytic infiltration and a high serum IgG4 level. A renal biopsy is necessary to diagnose IgG4RKD in patients without any lesions in other organs. Nephrologists typically perform renal biopsies in patients with abnormal urinalysis, such as proteinuria or hematuria, or renal failure. However, we experienced a patient with IgG4RKD without abnormalities in the urinalysis, renal function or imaging, who had severe interstitial lesions. We therefore propose that renal biopsies should be considered if patients do not show abnormal urinalysis findings and are suspected to have IgG4RKD.

Ultrastructural studies of IgG4-related kidney disease

OBJECTIVE

Ultrastructural studies of IgG4-related kidney disease (IgG4-RKD) characterized by tubulointerstitial nephritis (TIN) are limited in previous reports due to the rarity of the condition. In the present report, we performed ultrastructural examinations and assessed the pathogenesis of this disease.

PATIENTS

Clinicopathological studies were conducted in eight patients diagnosed with IgG4-RKD. Routine light, immunofluorescence and electron microscopy examinations and immunohistochemical assessments of IgG4 were performed using renal biopsy samples.

RESULTS

Hypocomplementemia, positive anti-nuclear antibodies and eosinophilia were confirmed in more than half of the cases. Electron dense deposits (EDDs) were frequently found in the glomeruli and interstitium. The rate of deposition was 62.5% in both mesangial areas and Bowman's capsule. EDDs were frequently detected on the tubular basement membrane (TBM) (87.5% of patients). The interstitium also contained EDDs on collagen fibers in 87.5% of the cases and on basement membrane-like materials in areas of fibrosis in 37.5% of the cases. The creatinine clearance levels were significantly lower in the patients with the latter pattern. Meanwhile, the rate of immunoglobulin and/or complement deposition on the TBM was observed in less than 37.5% of patients, and these findings were not entirely coincident with the cases of EDDs on the TBM.

CONCLUSION

EDDs are frequently found in the glomeruli and interstitium in patients with IgG4-RKD; however, immunohistological studies do not provide evidence that IgG4-RKD involves TIN with immune complex nephropathy. The presence of interstitial EDDs may be related to the progression of interstitial fibrosis in the setting of IgG4-RKD.

Acute Interstitial Nephritis and Membranous Nephropathy in the Context of IgG4-Related Disease

We present the case of a patient with IgG4-related disease, which manifested in an asynchronous manner as vitiligo, cholecystitis, sialadenitis, lymphadenopathy, facial palsy and kidney dysfunction. The patient underwent a renal biopsy, and a presumptive diagnosis of lupus nephritis was made due to compatible clinical and immunological findings. The biopsy revealed IgG4-related kidney disease with severe interstitial nephritis and membranous nephropathy. Corticosteroids treatment restored all disease manifestations. We bring this case to the attention of the nephrologists because of the protean, asynchronous, multisystemic nature of the disease that necessitates a multidisciplinary approach, a low threshold for kidney biopsy and a high index of suspicion for making the correct diagnosis and treatment.

Tubulointerstitial fibrosis in patients with IgG4-related kidney disease: pathological findings on repeat renal biopsy

Renal parenchymal lesions in patients with IgG4-related kidney disease (IgG4-RKD) are characterized by tubulointerstitial nephritis with storiform fibrosis and infiltration by high numbers of IgG4-positive plasma cells. The aim of this study was to evaluate the clinical and pathological effects of corticosteroid therapy in patients with IgG4-RKD. Of six patients who were diagnosed with IgG4-RKD, four patients underwent re-biopsy at approximately 30-50 days after corticosteroid therapy was initiated. Based on the classification of Yamaguchi et al., the degree of tubulointerstitial fibrosis was classified before and after therapy. In addition, tubulointerstitial expression patterns of α-smooth muscle actin (α-SMA), collagen I, III, and IV protein, and connective tissue growth factor (CTGF) mRNA were examined. Histopathological findings before treatment showed α-SMA-positive myofibroblasts in the lesion, and CTGF mRNA-positive cells were found in the cellular infiltrate. Although corticosteroid therapy improved serum creatinine clinically, the stage of fibrosis advanced pathologically as evidenced by increased staining for collagen I and III. However, the number of IgG4-positive plasma cells decreased, and CTGF mRNA expression reduced. In other words, fibrosis had advanced from the time of extensive cell infiltration in patients with IgG4-RKD and inflammation was relieved by corticosteroid. A reduced number of positive CTGF mRNA expression cells in repeat biopsies indicated that the fibrosis process was terminated by corticosteroid therapy. We propose that corticosteroid therapy could terminate the pathway of active fibrosis, thereby inhibiting progression to renal dysfunction.

Acute interstitial nephritis - a reappraisal and update

Acute interstitial nephritis (AIN) is an under recognized and under diagnosed cause of acute kidney injury (AKI). It is estimated to account for 15 - 20% of cases of AKI; it is the reported diagnosis in 2.8% of all kidney biopsies, and 13.5% of biopsies done specifically for acute renal failure. Considerable evidence implicates antigen initiated cell-mediated injury in the pathogenesis of AIN. Drugs account for 70% of all cases, with over 150 different agents incriminated. The remaining cases are due to infections, autoimmune diseases, and rarely idiopathic. The central component of renal injury in AIN is altered tubular function, which usually precedes decrements in filtration rate. The key to early diagnosis is vigilance for the presence of tubular dysfunction in non-oliguric individuals, especially in patients with modest but gradual increments in creatinine level. The utility of urinary biomarkers to diagnose AIN in its early nascent and potentially reversible stage remains to be determined. Prompt recognition, elimination of the offending source of antigen, and use of a limited course of steroid therapy where indicated, will result in complete resolution in ~ 65% of cases, partial resolution in up to 20%, and irreversible damage in the rest.

Idiopathic membranous nephropathy and IgG4: an interesting relationship

Idiopathic membranous nephropathy (iMN) is a single-organ autoimmune disease characterized by subepithelial deposition of immune complexes containing IgG4 resulting in proteinuria, nephrotic syndrome, and, in some, end-stage renal disease. The pathogenesis involves a chronic IgG4 response against specific podocyte antigens which have now been at least partially defined in the neonatal, early childhood, and adult varieties. More has recently been learned about the genetic predisposition as well. This review discusses the pathophysiology of iMN in light of these discoveries and what is known about the genesis and potential clinical ramifications of an antigen-specific IgG4 response.

IgG4-related tubulointerstitial nephritis accompanied with cystic formation

Background

An immunoglobulin G4 (IgG4)-related disease is important disease in differential diagnosis of tumors in kidney, pancreas, lung and other organs. The imaging findings of IgG4-related kidney diseases are usually expressed as defect contrast region, while cystic formation in kidney is extremely rare. Here, we report a case of IgG4-related tubulointerstitial nephritis with renal cystic change caused by the narrowing or obstruction of collecting duct in renal medulla.

Case presentation

Abdominal contrasted CT scan showed a 31 × 24 mm cystic tumor at the upper pole of the right kidney and multiple low-attenuation areas in the left kidney. ¹⁸ F-fluorodeoxyglucose (FDG)-PET/CT scan showed moderate FDG accumulation of cystic tumor in marginal lesion. In addition, FDG-PET/CT scan also showed moderate FDG accumulation in the pancreatic body. Laparoscopic right nephrectomy was performed. Histological examination was revealed lymphoplasmacytic infiltrate with focal fibrosis and severe narrowing or obstruction of lumen of collecting duct in renal medulla. Furthermore, the IgG4 positive plasma cells infiltrated exceeding 10 cells per one high-power field in renal medulla. The ratio of IgG4-plasma cells to IgG-positive plasma cells was about 50%. The serum level of IgG4 was also elevated (218 mg/dl). Based on these findings, we finally diagnosed IgG4-related tubulointerstitial nephritis with renal cystic change.

Conclusion

IgG4-related kidney disease might cause cystic formation by severe narrowing and obstruction of collecting duct.

IgG4- related disease: an orphan disease with many faces

Immunoglobulin G4- related disease (IgG4-RD) is a rare systemic fibro-inflammatory disorder (ORPHA284264). Although patients have been described more than 100 years ago, the systemic nature of this disease has been recognized in the 21^st century only. Type 1 autoimmune pancreatitis is the most frequent manifestation of IgG4-RD. However, IgG4-RD can affect any organ such as salivary glands, orbits, retroperitoneum and many others. Recent research enabled a clear clinical and histopathological description of IgG4-RD. Typically, lymphoplasmacellular inflammation, storiform fibrosis and obliterative phlebitis are found in IgG4-RD biopsies and the tissue invading plasma cells largely produce IgG4. Elevated serum IgG4 levels are found in many but not all patients. Consequently, diagnostic criteria for IgG4-RD have been proposed recently. Treatment is largely based on clinical experience and retrospective case series. Glucocorticoids are the mainstay of therapy, although adjunctive immunosuppressive agents are used in relapsing patients. This review summarizes current knowledge on clinical manifestations, pathophysiology and treatment of IgG4-RD.

IgG4-related disease and its pathogenesis-cross-talk between innate and acquired immunity

IgG4-RD, a novel disease involving many immune-system components

IgG4-related disease (IgG4-RD) is a novel clinical entity proposed in Japan in the 21th century and is attracting strong attention over the world. The characteristic manifestations of IgG4-RD are increased serum IgG4 concentration and tumefaction by IgG4⁺ plasma cells. Although the clinical manifestations in various organs have been established, the pathogenesis of IgG4-RD is still unknown. Recently, many reports of aberrant acquired immunity such as T_h2-diminated immune responses have been published. However, many questions still remain, including questions about the pathogenesis of IgG4-RD and the roles of IgG4. In this review, we discuss the pathogenesis of IgG4-RD by focusing on the cross-talk between innate and acquired immunity.

IgG4-Related Tubulointerstitial Nephritis Associated with Membranous Nephropathy in Two Patients: Remission after Administering a Combination of Steroid and Mizoribine

We report two cases of Japanese men who presented with proteinuria, eosinophilia, hypocomplementemia, and high serum immunoglobulin G4 (IgG4) concentration and were diagnosed with membranous nephropathy associated with IgG4-related tubulointerstitial nephritis on renal biopsy. The typical renal lesions of IgG4-related disease are tubulointerstitial nephritis, which improves remarkably with steroid therapy, and occasional glomerular changes. In our two cases, renal biopsy revealed IgG4-positive immune complex deposits in glomeruli in a pattern of membranous nephropathy and concurrent tubulointerstitial nephritis with IgG4 plasma cells. In both cases, proteinuria persisted with initial prednisolone treatment and was resolved only after the addition of mizoribine. We report the first two cases in which the combination of prednisolone and mizoribine was effective for treating membranous nephropathy associated with IgG4-related tubulointerstitial nephritis.

IgG4- related disease as a rare cause of tubulointerstitial nephritis

Isolated IgG4 tubulointerstitial nephritis (TIN) is a rare disorder characterized by raised serum IgG4 levels and histological findings of dense lymphoplasmacytic infiltrates rich in IgG4 positive plasma cells. We report a case of isolated IgG4 TIN that presented with acute kidney injury in an 84 year old man with a polyclonal increase in his total IgG and a raised IgE of 381 kUA/L but without evidence of systemic autoimmunity. We draw a parallel with IgG4-related autoimmune pancreatitis and show raised levels of circulating regulatory T cells. Importantly the plasma levels of the T regulatory cell cytokine, IL10, the TH1 cytokines IL12 and IFNγ, the proinflammatory TNF α and immune regulatory IL27 were all highly raised. Furthermore, the level of IL21 that promotes IgG4 production was also very significantly elevated. These results suggest efforts of the immune system to reduce inflammation and suppress an exaggerated Th2 response. A raised serum IgG in the setting of acute kidney injury and in the absence of autoimmunity and chronic infection should encourage an assessment of the IgG subclasses. Prompt steroid treatment of those with a raised IgG4 may reduce ongoing renal damage.

IgG4-related kidney disease: MRI findings with emphasis on the usefulness of diffusion-weighted imaging

OBJECTIVES

To investigate the imaging findings of immunoglobulin G4 (IgG4)-related kidney disease (IgG4-KD) on magnetic resonance imaging (MRI) including diffusion-weighted imaging (DWI) and to evaluate the usefulness of DWI in lesion detection.

METHODS

This retrospective cohort study included 31 patients with IgG4-KD who underwent MRI covering both kidneys. Two radiologists reviewed in consensus the MR images to determine the distribution pattern (location, laterality, and multiplicity) and the visually assessed signal intensity (hypointense, isointense or hyperintense) of the renal lesions compared to the normal renal parenchyma on each sequence. Per-patient sensitivity for detecting IgG4-KD and the number of detectable lesions were compared in T2-weighted images, DWI, and dynamic contrast-enhanced images.

RESULTS

IgG4-KD typically manifested as bilateral (83.9%), multiple (93.5%), and renal parenchymal (87.1%) nodules appearing isointense (93.5%) on T1-weighted images, hypointense (77.4%) on T2-weighted images, hyperintense (100%) on DWI (b=1000), and hypointense (83.3%) in the arterial phase and with a progressive enhancement pattern on dynamic contrast-enhanced images. The sensitivity of DWI for detecting IgG4-KD was significantly higher than that of T2-weighted images (100% vs. 77.4%, P=0.034). The median number of detectable lesions was significantly greater in DWI (n=9) than in T2-weighted images (n=2) and dynamic contrast-enhanced images (n=5) (P≤0.008).

CONCLUSIONS

The characteristic MRI findings of IgG4-KD were bilateral, multiple, renal parenchymal nodules with T2 hypointensity, diffusion restriction, and a progressive enhancement pattern. As DWI was useful in the detection of IgG4-KD, adding DWI to conventional MRI for patients suspected of having IgG4-KD may enhance the diagnosis.

IgG4-related disease

Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is an immune-mediated condition that can affect almost any organ and is now being recognized with increasing frequency. IgG4-RD is characterized by a lymphoplasmacytic infiltrate composed of IgG4(+) plasma cells, storiform fibrosis, obliterative phlebitis, and mild to moderate eosinophilia. The diagnosis of IgG4-RD unifies many eponymous fibroinflammatory conditions that had previously been thought to be confined to single organs. IgG4-RD lesions are infiltrated by T helper cells, which likely cause progressive fibrosis and organ damage. IgG4 antibodies are generally regarded as noninflammatory. Although autoreactive IgG4 antibodies are observed in IgG4-RD, there is no evidence that they are directly pathogenic. Rituximab-induced B cell depletion in IgG4-RD leads to rapid clinical and histological improvement accompanied by swift declines in serum IgG4 concentrations. Although IgG autoantibodies against various exocrine gland antigens have been described in IgG4-RD, whether they are members of the IgG4 subclass is unknown. The contribution of autoantibodies to IgG4-RD remains unclear.

A Retrospectively Diagnosed Case of IgG4-Related Tubulointerstitial Nephritis Showing Good Renal Outcome and Pathological Progress

A 74-year-old man was hospitalized for diabetic nephropathy evaluation and assessment of the effect of treatment on his tubulointerstitial nephritis (TIN). When he was 62 years old, he developed polyarthralgia and had superficial lymph node swelling, mildly increased serum creatinine concentration, hypergammaglobulinemia, hypocomplementemia, high serum IL-2R level, and positive titer of antinuclear antibody. Several tissues were biopsied. Mild chronic sialadenitis and reactive lymphadenitis were identified. Renal specimen showed mild glomerular ischemia, extensive storiform fibrosis, and abundant infiltrating monocytes and plasma cells. He was treated with oral prednisolone and cyclophosphamide. After the treatment, most of his clinical parameters quickly returned to within the reference range. However, he developed diabetes mellitus soon after steroid therapy. At the time of rebiopsy, a high level of serum IgG4 was detected. The second renal biopsy showed diabetic nephropathy without any tubulointerstitial damage. The first biopsied tissues were retrospectively investigated. Large numbers of IgG4-positive plasma cells were detected in the kidneys and lymph nodes. A retrospective diagnosis of IgG4-related TIN with lymph node involvement was made. In conclusion, this paper describes a retrospectively diagnosed case of IgG4-related TIN with lymph node involvement, showing good clinical and pathological prognosis.

Leptospira Interrogans induces fibrosis in the mouse kidney through Inos-dependent, TLR- and NLR-independent signaling pathways

Background

Leptospira (L.) interrogans are bacteria responsible for a worldwide reemerging zoonosis. Rodents carry L. interrogans asymptomatically in their kidneys and excrete bacteria in the urine, contaminating the environment. Humans get infected through skin contact and develop a mild or severe leptospirosis that may lead to renal failure and fibrosis. L. interrogans provoke an interstitial nephritis, but the induction of fibrosis caused by L. interrogans has not been studied in murine models. Innate immune receptors from the TLR and NLR families have recently been shown to play a role in the development and progression of tissue fibrosis in the lung, liver and kidneys under different pathophysiological situations. We recently showed that TLR2, TLR4, and NLRP3 receptors were crucial in the defense against leptospirosis. Moreover, infection of a human cell line with L. interrogans was shown to induce TLR2-dependent production of fibronectin, a component of the extracellular matrix. Therefore, we thought to assess the presence of renal fibrosis in L. interrogans infected mice and to analyze the contribution of some innate immune pathways in this process.

Methodology/principal findings

Here, we characterized by immunohistochemical studies and quantitative real-time PCR, a model of Leptospira-infected C57BL/6J mice, with chronic carriage of L. interrogans inducing mild renal fibrosis. Using various strains of transgenic mice, we determined that the renal infiltrates of T cells and, unexpectedly, TLR and NLR receptors, are not required to generate Leptospira-induced renal fibrosis. We also show that the iNOS enzyme, known to play a role in Leptospira-induced interstitial nephritis, also plays a role in the induction of renal fibrosis.

Conclusion/significance

To our knowledge, this work provides the first experimental murine model of sustained renal fibrosis induced by a chronic bacterial infection that may be peculiar, since it does not rely on TLR or NLR receptors. This model may prove useful to test future therapeutic strategies to combat Leptospira-induced renal lesions.

Leptospirosis is a bacterial disease transmitted by asymptomatic rodents to humans. The symptoms may be mild, or severe with kidney failure. Renal fibrosis, occurring during inflammatory situations, is characterized by the pathological accumulation of extra-cellular matrix components and can compromise the kidney functions of patients with leptospirosis. Recent research revealed that both innate and adaptive immune responses are involved in the establishment of fibrosis, in several organs and in different pathophysiological situations. In the present study, we characterized a mouse model of chronic infection with Leptospira that provokes mild renal fibrosis. We show that fibrogenesis requires the presence of live Leptospira in the kidney and that B and T cells from the adaptive immune response do not participate in the induction of renal fibrosis. Unexpectedly, we also found that innate immune receptors, TLRs and NLRs, are not involved in the Leptospira-induced fibrosis. Finally, we show that the enzyme responsible for NO production, iNOS, known to participate in renal inflammatory lesions induced by Leptospira, is also involved in renal fibrosis. Our work provides a novel mouse model to study fibrosis occurring due to leptospirosis.

Mechanisms and assessment of IgG4-related disease: lessons for the rheumatologist

Recognition of IgG4-related disease as an independent chronic inflammatory disorder is a relatively new concept; previously, the condition was thought to represent a subtype of Sjögren's syndrome. IgG4-related disease is characterized by elevated serum levels of IgG4 and inflammation of various organs, with abundant infiltration of IgG4-bearing plasma cells, storiform fibrosis and obliterative phlebitis representing the major histopathological features of the swollen organs. The aetiology and pathogenesis of this disorder remain unclear, but inflammation and subsequent fibrosis occur due to excess production of type 2 T-helper-cell and regulatory T-cell cytokines. The disease can comprise various organ manifestations, such as dacryoadenitis and sialadenitis (also called Mikulicz disease), type 1 autoimmune pancreatitis, kidney dysfunction and lung disease. Early intervention using glucocorticoids can improve IgG4-related organ dysfunction; however, patients often relapse when doses of these agents are tapered. The disease has also been associated with an increased incidence of certain malignancies. Increased awareness of IgG4-related disease might lead to consultation with rheumatologists owing to its clinical, and potentially pathogenetic, similarities with certain rheumatic disorders. With this in mind, we describe the pathogenic mechanisms of IgG4-related disease, and outline considerations for diagnosis and treatment of the condition.

IgG4-related kidney disease

IgG4-related kidney disease (IgG4-RKD) is a comprehensive term for renal lesions associated with IgG4-related disease, which is a recently recognized clinical entity characterized by a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells with fibrosis affecting several organs. Tubulointerstitial nephritis with increased IgG4-positive plasma cells and fibrosis is the most dominant feature of IgG4-RKD and may cause acute or chronic renal dysfunction, although some glomerular lesions such as membranous nephropathy are sometimes evident. Radiologically, several characteristic abnormalities are often demonstrated, sometimes mimicking malignancies. IgG4-RKD predominantly affects middle-aged to elderly men, and most patients have accompanying IgG4-related extrarenal lesions such as sialadenitis, lymphadenopathy, or type 1 autoimmune pancreatitis. Serology usually demonstrates high levels of serum total IgG and IgG4, and high levels of serum IgE and hypocomplementemia are also frequent features. Corticosteroid therapy is usually quite effective, leading to amelioration of the renal dysfunction and radiological and serological abnormalities. However, as any delay in treatment may result in irreversible renal failure, early diagnosis and appropriate therapy are very important. Despite these distinctive clinicopathological features of IgG4-RKD, its pathogenesis remains poorly understood. Awareness of this condition and accumulation of more cases worldwide are necessary.

IgG4 related interstitial nephritis: A case report and review of literature

IgG4 interstitial nephritis is a recently described entity. A middle-aged gentleman with bilateral parotid enlargement, hepatosplenomegaly and generalized lymphadenopathy was referred to us for evaluation of renal failure. He had trace proteinuria and large kidneys. Kidney biopsy revealed interstitial nephritis with characteristic storiform fibrosis. Immunohistochemistry demonstrated intense staining for IgG4-secreting plasma cells in the interstitium.

Renal disease masquerading as pyrexia of unknown origin

Pyrexia of unknown origin is a challenging clinical problem. Infections, malignancies, and connective tissue diseases form the major etiologies for this condition. We report a case of a 57-year-old diabetic male who presented with fever of unknown origin for several months. The course of investigations led to a kidney biopsy which clinched the cause of his fever as well as the underlying diagnosis. The light microscopy findings of expansile storiform fibrosis with a dense inflammatory infiltrate suggested the diagnosis which was confirmed by positive staining of Immunoglobulin G4, the dense lympho-plasmacytic infiltrate and elevated serum IgG4 concentrations. A course of steroids followed by mycophenolate mofetil as maintenance immunosuppression rendered the patient afebrile with improvement of renal function.

IgG4: a tantalizing link between causes of membranous glomerulonephritis and systemic disease

Alexander et al. give a detailed description of IgG4-related membranous glomerulonephritis (MGN). Their data delineate for the first time in IgG4-related disease (IgG4-RD) a second pattern of tissue injury occurring within the same organ. The paper highlights that MGN can occur alone or simultaneously with IgG4-related tubulointerstitial nephritis. Thus, it extends our understanding of IgG4-RD and illuminates potential pathways for new investigations into its pathophysiology.

Development of IgG4-related disease in a patient diagnosed with idiopathic membranous nephropathy

We report a case of IgG4-related disease (IgG4-RD) diagnosed after 3 years of follow-up for idiopathic membranous nephropathy (MN). MN has been considered as glomerular lesion of IgG4-related kidney diseases in recent years and was diagnosed simultaneously with or after a diagnosis of IgG4-RD in previously reported cases. In the present case, IgG4-RD developed 3 years after the diagnosis of idiopathic MN, indicating a possible relationship between idiopathic MN and IgG4-RD through common underlying mechanisms of development.