Membranoproliferative glomerulonephritis pathophysiology: Difference between revisions
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==Overview== | ==Overview== | ||
==Pathophysiology== | ==Pathophysiology== | ||
* '''Type I MPGN''': It results from chronic antigenemia and the generation of nephritogenic immune complexes that localize to the subendothelial spaces.Recent studies have demonstrated the contribution of innate immunity to both the generation of antibodies that are deposited as immune complexes and to the local inflammatory responses directed at the glomerular immune deposits.The immune complexes activate the complement system via the classical pathway, leading to the generation of chemotactic factors (C3a, C5a) that mediate the accumulation of platelets and leukocytes and of terminal components (C5b-9) that directly induce cell injury. Leukocytes release oxidants and proteases that mediate capillary wall damage and cause proteinuria. Cytokines and growth factors released by glomerular cells lead to mesangial proliferation and expansion. | |||
* '''Type II MPGN''': It results from the uncontrolled systemic activation of the alternative pathway of the complement cascade . In most patients, loss of complement regulation is caused by the C3 nephritic factor , an immunoglobulin (Ig)G autoantibody that binds and prevents the inactivation of C3 convertase (C3bBb) of the alternative pathway, which results in the breakdown of C3. Another cause of type II MPGN is due to mutations in the complement regulatory protein, factor H, or to autoantibodies that impede factor H function, highlighting the role of deregulated alternative complement pathway activity in type II MPGN. | |||
* '''Type III MPGN''': It is thought to be result due to a slow-acting nephritic factor that stabilizes a properdin dependent C5-convertase, (Cb3)2BbP, activating the terminal pathway of the complement. This nephritic factor has not been reported in healthy subjects, unlike C3NeF. In addition, the deposits observed in renal biopsies of patients with type III MPGN are closely associated with the circulating nephritic factor-stabilized convertase and with hypocomplementemia, suggesting that NeFt is fundamental to the pathogenesis of type III MPGN. | |||
* '''Cryoglobulinemic MPGN''' : The mechanism of renal injury in HCV-associated cryoglobulinemia remains elusive. A large percentage of patients with chronic HCV infection develop type II cryoglobulins. However, only a minority of such patients with detectible cryoglobulinemia have clinical manifestations of cryoglobulinemic MPGN. It is unclear why some cryoglobulins are more pathogenic than others, or why cryoglobulins deposit in the kidneys. Recognition of the components of cryoprecipitates, which contain HCV core protein, by circulating leukocytes and intrinsic glomerular cells leads to the production of inflammatory mediators that characterize the glomerular injury of cryoglobulinemic MPGN. | |||
==Histologic Findings== | ==Histologic Findings== | ||
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Revision as of 21:08, 10 June 2018
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Membranoproliferative glomerulonephritis Microchapters |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Ali Poyan Mehr, M.D. [2] Associate Editor(s)-in-Chief: Olufunmilola Olubukola M.D.[3]
Overview
Pathophysiology
- Type I MPGN: It results from chronic antigenemia and the generation of nephritogenic immune complexes that localize to the subendothelial spaces.Recent studies have demonstrated the contribution of innate immunity to both the generation of antibodies that are deposited as immune complexes and to the local inflammatory responses directed at the glomerular immune deposits.The immune complexes activate the complement system via the classical pathway, leading to the generation of chemotactic factors (C3a, C5a) that mediate the accumulation of platelets and leukocytes and of terminal components (C5b-9) that directly induce cell injury. Leukocytes release oxidants and proteases that mediate capillary wall damage and cause proteinuria. Cytokines and growth factors released by glomerular cells lead to mesangial proliferation and expansion.
- Type II MPGN: It results from the uncontrolled systemic activation of the alternative pathway of the complement cascade . In most patients, loss of complement regulation is caused by the C3 nephritic factor , an immunoglobulin (Ig)G autoantibody that binds and prevents the inactivation of C3 convertase (C3bBb) of the alternative pathway, which results in the breakdown of C3. Another cause of type II MPGN is due to mutations in the complement regulatory protein, factor H, or to autoantibodies that impede factor H function, highlighting the role of deregulated alternative complement pathway activity in type II MPGN.
- Type III MPGN: It is thought to be result due to a slow-acting nephritic factor that stabilizes a properdin dependent C5-convertase, (Cb3)2BbP, activating the terminal pathway of the complement. This nephritic factor has not been reported in healthy subjects, unlike C3NeF. In addition, the deposits observed in renal biopsies of patients with type III MPGN are closely associated with the circulating nephritic factor-stabilized convertase and with hypocomplementemia, suggesting that NeFt is fundamental to the pathogenesis of type III MPGN.
- Cryoglobulinemic MPGN : The mechanism of renal injury in HCV-associated cryoglobulinemia remains elusive. A large percentage of patients with chronic HCV infection develop type II cryoglobulins. However, only a minority of such patients with detectible cryoglobulinemia have clinical manifestations of cryoglobulinemic MPGN. It is unclear why some cryoglobulins are more pathogenic than others, or why cryoglobulins deposit in the kidneys. Recognition of the components of cryoprecipitates, which contain HCV core protein, by circulating leukocytes and intrinsic glomerular cells leads to the production of inflammatory mediators that characterize the glomerular injury of cryoglobulinemic MPGN.
Histologic Findings
Light microscopy
Glomeruli generally are enlarged and hypercellular, with an increase in mesangial cellularity and matrix. Mesangial increase, when generalized throughout the glomeruli, causes an exaggeration of their lobular form, giving rise to the alternative name of lobular nephritis. Infiltrating neutrophils and monocytes contribute to glomerular hypercellularity.
The capillary basement membranes are thickened by interposition of mesangial cells and matrix into the capillary wall. This gives rise to the tram-track or double-contoured appearance of the capillary wall, best appreciated with the methenamine silver stain or the periodic acid-Schiff reagent.
Crescents may be visible in 10% of patient biopsy specimens. Interstitial changes, including inflammation, interstitial fibrosis, and tubular atrophy, are observed in patients with progressive decline in GFR.
https://commons.wikimedia.org/wiki/File:Membranoproliferative_glomerulonephritis_-_very_high_mag.jpg
Membranoproliferative glomerulonephritis type I
The most common type of MPGN is type1. It is described as Immune complex mediated MPGN, with circulating immune complexes present in approximately 33% of patients with MPGN type I. In all patients with type I, immune complexes are found in the mesangium and subendothelial spaces. The most common causes of immune complex MPGN include chronic infections, autoimmune diseases, and monoclonal gammopathies. Monoclonal gammopathies have been recently recognized as an important cause of MPGN, especially in older adults, with or without cryoglobulins [1]. About 41% of patients without chronic infections or autoimmune diseases had serum and/or urine electrophoresis studies positive for a monoclonal gammopathy [1]. Most of them had a monoclonal gammopathy of undetermined significance
On electron microscopy, electron dense deposits in subendothelial sites are characteristic of this disease. Mesangial and occasional subepithelial deposits also may be present. Irregular new basement membrane material is formed around the subendothelial deposits and mesangial projections, producing the tram-track appearance on light microscopy.
By immunofluorescence, prominent C3 deposition in a granular pattern is noted in the capillary walls, with variable mesangial C3 deposits. Early components of complement, immunoglobulin G (IgG), and, less commonly, immunoglobulin M (IgM) may be found in a distribution similar to C3.
Membranoproliferative glomerulonephritis type II or dense deposit disease
The basement membranes of the glomerulus, Bowman capsule, tubules, and peritubular capillaries are thickened. The basement membrane appears irregular and ribbonlike on special stains (eg, periodic acid-Schiff, thioflavine-T, toluidine blue).
On electron microscopy, the basement membrane is thickened by discontinuous, amorphous electron dense deposits that reside in the lamina densa layer, hence the alternative name of dense deposit disease. Mesangial and subepithelial dense deposits may be noted.
Immunofluorescence reveals complement component C3 deposited in an irregular granular pattern in the basement membranes on either side but not within the dense deposits or in nodular ring forms in the mesangium. Little or no deposition of immunoglobulins occurs in the glomeruli.
Membranoproliferative glomerulonephritis type III
This variant of MPGN, also called the Burkholder variant, displays combined features of MPGN type I and membranous nephropathy.
Subepithelial, subendothelial, and mesangial deposits are present on electron microscopy. Successive generations of subendothelial and subepithelial deposits disrupt the basement membrane, and concurrent formation of new lamina densa material is present, giving the basement membrane a complex laminated appearance.
Immunohistology shows granular deposition of C3, C5, properdin, IgG, and IgM, predominantly in the capillary walls.
References
- ↑ 1.0 1.1 Sethi S, Zand L, Leung N, Smith RJ, Jevremonic D, Herrmann SS; et al. (2010). "Membranoproliferative glomerulonephritis secondary to monoclonal gammopathy". Clin J Am Soc Nephrol. 5 (5): 770–82. doi:10.2215/CJN.06760909. PMC 2863981. PMID 20185597.