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      Membranous nephropathy with solitary polyclonal IgA deposition: A case report and literature review

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          Abstract

          A 60-year-old man presented with nephrotic syndrome (NS). Light microscopy of renal biopsy specimens showed minor glomerular abnormalities, while immunofluorescence microscopy revealed solitary polyclonal granular IgA deposition along the glomerular capillary walls. Electron microscopy showed small amounts of electron-dense deposits in the subepithelial area, but not in the mesangial area. In this patient, apparent underlying disease was not found during the 3-year follow-up, and low-dose prednisolone was effective in the treatment of NS. To our knowledge, there is only one case report of membranous nephropathy with clinicopathological features similar to our case.

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          Primary Membranous Nephropathy.

          Membranous nephropathy (MN) is a unique glomerular lesion that is the most common cause of idiopathic nephrotic syndrome in nondiabetic white adults. About 80% of cases are renal limited (primary MN, PMN) and 20% are associated with other systemic diseases or exposures (secondary MN). This review focuses only on PMN. Most cases of PMN have circulating IgG4 autoantibody to the podocyte membrane antigen PLA2R (70%), biopsy evidence PLA2R staining indicating recent immunologic disease activity despite negative serum antibody levels (15%), or serum anti-THSD7A (3%-5%). The remaining 10% without demonstrable anti-PLA2R/THSd7A antibody or antigen likely have PMN probably secondary to a different, still unidentified, anti-podocyte antibody. Considerable clinical and experimental data now suggests these antibodies are pathogenic. Clinically, 80% of patients with PMN present with nephrotic syndrome and 20% with non-nephrotic proteinuria. Untreated, about one third undergo spontaneous remission, especially those with absent or low anti-PLA2R levels, one-third progress to ESRD over 10 years, and the remainder develop nonprogressive CKD. Proteinuria can persist for months after circulating anti-PLA2R/THSD7A antibody is no longer detectable (immunologic remission). All patients with PMN should be treated with supportive care from the time of diagnosis to minimize protein excretion. Patients with elevated anti-PLA2R/THSD7A levels and proteinuria >3.5 g/d at diagnosis, and those who fail to reduce proteinuria to <3.5 g after 6 months of supportive care or have complications of nephrotic syndrome, should be considered for immunosuppressive therapy. Accepted regimens include steroids/cyclophosphamide, calcineurin inhibitors, and B cell depletion. With proper management, only 10% or less will develop ESRD over the subsequent 10 years.
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            A New Classification System for IgG4 Autoantibodies

            IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus “blocking” their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein–protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky’s postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.
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              IgA-dominant postinfectious glomerulonephritis: a report of 13 cases with common ultrastructural features.

              A unique form of postinfectious glomerulonephritis characterized by IgA-dominant immune complex deposits was recently described by Nasr et al (Hum Pathol. 2003;34:1235-1241), each case after a Staphylococcus infection in diabetic patients. Others have described glomerulonephritis with IgA-containing immune complex deposits in association with staphylococcal infections, although their histology was more varied and electron microscopy often did not to show large subepithelial deposits ("humps") typical of postinfectious glomerulonephritis. In this report, we describe demographic, clinical, and renal biopsy findings in 13 cases of IgA-dominant postinfectious glomerulonephritis, each characterized by subepithelial humps at various stages of resolution. All patients presented with renal insufficiency (mean serum creatinine +/- SD, 4.4 +/- 2.7 mg/dL), hematuria (macroscopic in 3), and proteinuria (nephrotic range in 6). Based on histology and electron microscopy, postinfectious glomerulonephritis was classified as acute in 2 patients, subacute in 3, and resolving/persistent in 8. There were 6 patients who had recent Staphylococcus aureus infections (3 methicillin resistant), 5 who were diabetic, and 3 with nephropathy. A total of 4 patients (3 with serum creatinine >8.0 mg/dL at biopsy) developed end-stage renal disease, whereas 9 had a mean serum creatinine of 2.0 +/- 1.1 mg/dL (range, 0.8-4.4) at 10 +/- 13 months (range, 2-44) after biopsy. In summary, IgA-dominant postinfectious glomerulonephritis resembles poststreptococcal glomerulonephritis in its histologic spectrum and electron microscopy findings, is often associated with staphylococcal infections, occurs in diabetics and nondiabetics, and may resolve if renal failure at presentation is not severe.
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                Author and article information

                Journal
                Clin Nephrol Case Stud
                Dustri
                Clinical Nephrology. Case Studies
                Dustri-Verlag Dr. Karl Feistle
                2196-5293
                2019
                28 October 2019
                : 7
                : 60-65
                Affiliations
                [1 ]Department of Hematology, Nephrology, and Rheumatology, Akita University Graduate School of Medicine,
                [2 ]Department of Internal Medicine, Honjo Daiichi Hospital,
                [3 ]Department of Life Science, Akita University Graduate School of Engineering Science, Akita, and
                [4 ]Department of Pathology, Jikei University School of Medicine, Tokyo, Japan
                Author notes
                Correspondence to Atsushi Komatsuda, MD Department of Hematology, Nephrology, and Rheumatology, Akita University Graduate School of Medicine, 1-1-1 Hondo, Akita City, Akita 010-8543, Japan komatsud@ 123456med.akita-u.ac.jp
                Article
                10.5414/CNCS109807
                6822057
                31673485
                c9d2d973-4eb4-4706-8950-a9d55346f00a
                © Dustri-Verlag Dr. K. Feistle

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 7 March 2019
                : 21 August 2019
                Categories
                Case Report
                Nephrology

                membranous nephropathy,rare disease,solitary polyclonal iga deposition

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