Immunoelectron microscopic localization of membrane attack complex and hepatitis B e antigen in membranous nephropathy

Complement Receptor 1 Enhancement in Recurrent Membranous Nephropathy Following Kidney Transplantation: A Case Report

Membranous nephropathy (MN) recurs in some kidney allograft patients, and recurrence increases graft failure rates. We present a unique case of recurrent MN in first and second allografts showing glomerular capillary wall-positivity for complement receptor 1 (CR1) consistent with immunoglobulin G (IgG). A man in his late 20s developed MN and started hemodialysis. MN recurred and caused graft loss after the first transplantation and recurred again soon after the second transplantation. The IgG subclass staining was almost consistently negative for IgG4 and phospholipase A2 receptor (PLA2R)-staining was negative. Recurrent MN of unknown etiology was considered. Mass spectrometry demonstrated that CR1 had increased in the transplanted kidney biopsies. Immunohistochemistry and immunofluorescence studies demonstrated CR1 colocalized with IgG along glomerular capillaries in this case, whereas CR1 was localized in podocytes with no colocalization of IgG in a control case of PLA2R-associated MN. Correlative light and immunoelectron microscopy showed localization of CR1 at the interface between electron-dense deposits and podocytes. Collectively, this case demonstrated a unique enhancement and localization of CR1. MN with enhancement of CR1 has not been reported to date. CR1 may be a candidate causative antigen in this case of recurrent MN, although further study is needed to investigate the pathogenesis of CR1.

Deposition of the Membrane Attack Complex in Healthy and Diseased Human Kidneys

The membrane attack complex-also known as C5b-9-is the end-product of the classical, lectin, and alternative complement pathways. It is thought to play an important role in the pathogenesis of various kidney diseases by causing cellular injury and tissue inflammation, resulting in sclerosis and fibrosis. These deleterious effects are, consequently, targeted in the development of novel therapies that inhibit the formation of C5b-9, such as eculizumab. To clarify how C5b-9 contributes to kidney disease and to predict which patients benefit from such therapy, knowledge on deposition of C5b-9 in the kidney is essential. Because immunohistochemical staining of C5b-9 has not been routinely conducted and never been compared across studies, we provide a review of studies on deposition of C5b-9 in healthy and diseased human kidneys. We describe techniques to stain deposits and compare the occurrence of deposits in healthy kidneys and in a wide spectrum of kidney diseases, including hypertensive nephropathy, diabetic nephropathy, membranous nephropathy, IgA nephropathy, lupus nephritis, C3 glomerulopathy, and thrombotic microangiopathies such as the atypical hemolytic uremic syndrome, vasculitis, interstitial nephritis, acute tubular necrosis, kidney tumors, and rejection of kidney transplants. We summarize how these deposits are related with other histological lesions and clinical characteristics. We evaluate the prognostic relevance of these deposits in the light of possible treatment with complement inhibitors.

Infection and glomerulonephritis

Glomerular injury, occurring either as primary glomerular disease or as part of a systemic disease process, is usually a result of immune-mediated mechanisms. The morphologic reaction pattern has a diverse spectrum of appearance, ranging from normal by light microscopy in minimal change disease to crescentic forms of glomerulonephritis, with conspicuous disruption of the normal glomerular morphology. The mechanisms of glomerular immune deposit formation include trapping of circulating antigen-antibody complexes and the in situ formation of immune complexes within the glomerulus. While the majority of postinfectious immune-complex-mediated glomerulonephritides are believed to result from the deposition of circulating antigen-antibody complexes, preformed outside of the kidney and secondarily deposited in the kidney, the notion of forming in situ antigen-antibody complexes to either planted antigens or to integral structural components of the glomerulus, through "cross-reacting" autoimmune reactions, is gaining popularity in a variety of forms of glomerulonephritides. Patients with HIV infection may develop a spectrum of renal pathology, the glomerular manifestations of which include both antigen-antibody complex and nonimmune-complex-mediated pathogenetic mechanisms. Similarly, patients with Streptococcal infections, Hepatitis B virus, or Hepatitis C virus infection may develop a spectrum of glomerulonephritides, which are predominantly immune-complex-mediated. Therapy for glomerular diseases due to HIV, hepatitis B, or C virus infections remains a challenge.

The spectrum of podocytopathies: a unifying view of glomerular diseases

Glomerular diseases encompass a broad array of clinicopathologically defined syndromes which together account for 90% of end-stage kidney disease costing $20 billion per annum to treat in the United States alone. Recent insights have defined the central role of the podocyte as both the regulator of glomerular development as well as the determinant of progression to glomerulosclerosis. We can now place all glomerular diseases within this spectrum of podocytopathies with predictable outcomes based on podocyte biology impacted by temporal, genetic, and environmental cues. This simplified construct is particularly useful to rationalize clinical effort toward podocyte preservation and prevention of progression as well as to focus basic research effort on understanding podocyte biology and for clinical research toward development of practical monitoring strategies for podocyte injury, dysfunction, and loss.

The frequency of hepatitis B virus infection in Greek patients with various types of glomerulonephritis

The frequency of hepatitis B surface antigen (HBsAg) was studied in the sera of 622 patients with glomerulonephritis (GN). The prevalence of HBs-antigenemia was 2.8% (18/622; eleven adults and seven children); the difference from 2.6% in the general population of Central and Southern Greece was not statistically significant (chi 2 = 0.01; p > 0.50). Two of the 11 HBsAg-seropositive adult patients with GN suffered from IgA nephropathy, one from IgA and membranous glomerulonephritis (MGN), four from diffuse proliferative GN, two from membranous GN and one each from crescentic GN and focal segmental glomerulosclerosis. Five children out of 12 with membranous glomerulonephritis, one out of 24 with IgA nephropathy and one out of 16 with focal segmental glomerulosclerosis had HBs-antigenemia. The frequency of HBs-antigenemia in children with MGN was 41.7%, which is significantly higher than in children with other types of GN (0.9%). All seropositive patients were asymptomatic HBsAg carriers, while one seropositive HBsAg child with MGN suffered from chronic persistent hepatitis. HBsAg was detected by the immunoperoxidase-antiperoxidase (PAP) method in the glomeruli of only 3 children with MGN and HBs antigenemia, while HBcAg was not detected in any case. Our study suggests that in the Greek population there is no increased prevalence of HBs-antigenemia in patients with glomerulonephritis. Moreover, HBsAg was not found to contribute in the pathogenesis of GN in adults but it may be associated with the pathogenesis of membranous GN in children.