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This glomerulopathy is also known with the names: mesangiocapillary GN, type I and type III membranoproliferative GN (MPGN), and lobular GN. Another disease that has always been associated with MPGN and that also we will discuss here is the dense deposit disease (DDD), traditionally known as type II MPGN, although this name is not correct since it is physiopathogenically and morphologically a different disease (Walker PD, et al. Dense deposit disease is not a membranoproliferative glomerulonephritis. Mod Pathol. 2007;20(6):605-16 [PubMed link]). Due to the variety of causes that can lead to morphological changes of MPGN, perhaps it would be better to refer to "MPGN" as a pattern of glomerular injury caused by various diseases
MPGN is characterized by thickening of the capillary walls accompanied by cellular, predominantly mesangial, proliferation in all or almost all the glomeruli. The increase in cellularity and mesangial matrix produces accentuation of the lobular aspect of the glomerular tuft (lobular GN). The thickening of the capillary walls is due to subendothelial deposits and mesangial interposition with formation of material similar to the glomerular basement membrane (GBM) in the internal aspect of the wall, or subendothelial space. In some cases the injury is focal and segmental.
MPGN was formerly classified as primary (idiopathic) type I, type II (DDD), or type III, or secondary MPGN. MPGN I, the most common form, is characterized by subendothelial deposits, and MPGN III has both subepithelial and subendothelial deposits. DDD is characterized by dense deposits in the glomerular basement membrane. As it was classified until some years ago, the type I and type III MPGN probably include cases mediated by immune complexes and cases of disease by alterations in the path of the complement. At present, it is preferable to classify them, according to IF, in immune complexes mediated MPGN and C3 glomerulopathy, which includes DDD and C3 glomerulonephritis.
Given recent advances in the understanding of the role of the alternative pathway of complement in MPGN, a practical approach is to view MPGN as immune-complex–mediated or complement-mediated. Thus, immune-complex–mediated MPGN may occur when there are increased levels of circulating immune complexes, and complement-mediated MPGN may occur because of disorders associated with dysregulation of the alternative pathway of complement (Sethi S, Fervenza FC. Membranoproliferative glomerulonephritis--a new look at an old entity. N Engl J Med. 2012;366(12):1119-31. [PubMed link]).
Immune-complex–mediated MPGN results from the deposition of immune complexes in the glomeruli owing to persistent antigenemia, with antigen-antibody immune complexes forming as a result of chronic infections, elevated levels of circulating immune complexes due to autoimmune diseases, or paraproteinemias due to monoclonal gammopathies. The immune complexes trigger the activation of the classical pathway of complement and the deposition of complement factors of the classical pathway and terminal complement pathway in the mesangium and along the capillary walls. In these cases immunofluorescence will show immunoglobulins (mainly IgG) in addition to complement.
Dysregulation of the alternative pathway can occur because of mutations in or autoantibodies to complement-regulating proteins. Mutations in proteins that regulate the assembly and activity of C3 convertase and degradation of C3b, such as factors H, I, and B and factor H–related protein 5, result in dysregulation of the alternative pathway. Similarly, antibodies to the complement-regulating proteins (such as factors H and B) and to C3 convertase itself can result in overactivity of the alternative pathway. Antibodies to C3 convertase (called C3 nephritic factor) stabilize the convertase and prolong its half-life by preventing its inactivation and degradation, thereby activating the alternative pathway. The deposition of these complement products and debris in the mesangium and subendothelial region triggers glomerular inflammation and leads to MPGN. Immunoglobulins are not directly involved; thus, complement-mediated MPGN is typically immunoglobulin-negative but complement-positive on immunofluorescence studies. (Sethi S, Fervenza FC. Membranoproliferative glomerulonephritis--a new look at an old entity. N Engl J Med. 2012;366(12):1119-31. [PubMed link]; Bomback AS, Appel GB. Pathogenesis of the C3 glomerulopathies and reclassification of MPGN. Nat Rev Nephrol. 2012. doi: 10.1038/nrneph.2012.213. [PubMed link])
Immunofluorescence findings are used to distinguish immune-complex–mediated MPGN from complement-mediated MPGN and can often point to a specific cause. For example, MPGN associated with monoclonal gammopathy shows monotypic immunoglobulin with kappa or lambda light-chain restriction. MPGN associated with hepatitis C infection typically shows IgM, IgG, C3, and kappa and lambda light chains. An MPGN pattern in association with autoimmune diseases often includes multiple immunoglobulins and complement proteins — IgG, IgM, IgA, C1q, C3, and kappa and lambda light chains. MPGN associated with alternative-pathway dysfunction is characterized by bright C3 immunostaining in the mesangium and along the capillary walls. The absence of marked immunoglobulin staining on immunofluorescence microscopy distinguishes MPGN due to alternative-pathway dysfunction from immune-complex–mediated MPGN.
MPGN without Immune Complexes or Complement: A pattern of injury consistent with MPGN is also noted in thrombotic microangiopathies resulting from injury to the endothelial cells. In the acute phase, mesangiolysis, endothelial swelling, and fibrin thrombi are present in the glomerular capillaries. As the process evolves into a reparative and chronic phase, mesangial expansion and remodeling of the glomerular capillary walls, including double-contour formation, take place. Thus, the healing phase of thrombotic thrombocytopenic purpura or hemolytic–uremic syndrome, atypical hemolytic–uremic syndrome associated with complement abnormalities, the antiphospholipid antibody syndrome, drug-induced thrombotic microangiopathies, nephropathy associated with bone marrow transplantation, radiation nephritis, malignant hypertension, and connective-tissue disorders can all present with an MPGN pattern of injury on biopsy. In thrombotic microangiopathies, immunoglobulin and complement are typically absent on immunofluorescence, and electron-dense deposits are not present in the mesangium or along the capillary walls on electron microscopy (Sethi S, Fervenza FC. Membranoproliferative glomerulonephritis--a new look at an old entity. N Engl J Med. 2012;366(12):1119-31. [PubMed link])
MPGN can be idiopathic or can be secondary to systemic diseases or infections: hepatitis C, hepatitis B, subacute bacterial endocarditis, syphilis, cryoglobulinemia, and others. The morphologic aspect does not allow an approach to the etiology in these cases, except if there are characteristic features of cryoglobulinemia. In lupus nephritis can also be found MPGN pattern, but usually it has a more irregular affectation of the glomeruli.
DDD etiology is not known and neither the composition of the dense material. Nevertheless, some works suggest that these deposits are constituted by biochemically modified GBM glycoproteins. Although the pathogenesis of DDD is not known, it is known that the “nephritic factor” (C3NeF) plays an important role in the disease. C3NeF is an IgG auto-antibody directed against C3 convertase (C3bBb) that blinds and stabilizes it, this allow activation of the alternative pathway of the complement by stabilization of C3 convertasa. C3NeF prolongs the half-life of C3 convertase by binding to either C3bBb or IgG-C3b-C3bBb of the assembled convertase. C3NeF slows down dissociation of factor Bb from the C3 convertase precursor, and as a result, this neoenzyme can interact with its substrates for a longer period of time. The exact mechanism by which this stabilization occurs is unknown and may vary among patients, consistent with suspected differences in C3NeF itself (Appel GB, et al. Membranoproliferative glomerulonephritis type II (dense deposit disease): an update. J Am Soc Nephrol. 2005;16:1392-403. [PubMed link]). See the paragraph above about dysregulation of the alternative pathway.
C3NeF is found in >80% of patients with DDD and 20-50% of patients with type I MPGN, although with lower levels in this last disease. Some patients with DDD present also acquired partial lipodystrophy and similar deposits to those glomerular in the ocular Bruch’s membrane beneath the retinal pigment epithelium and in basement membrane of the spleen sinusoids. The deposition of activated components of complement in adipose tissue results in the destruction of adipocytes in areas high in factor D (fD; adipsin) content causing lipodystrophy.
Some genetic alterations have been implicated in DDD: CFH (the gene encoding complement factor H), CFHR5 (the gene encoding factor H-related 5), and possibly other C3 related mutations (Martínez-Barricarte R, et al. Human C3 mutation reveals a mechanism of dense deposit disease pathogenesis and provides insights into complement activation and regulation. J Clin Invest. 2010;120:3702-12. [PubMed link]; Corchado JC, Smith RJ. Dense Deposit Disease/Membranoproliferative Glomerulonephritis Type II. In : GeneReviews, May 19, 2011.. www.ncbi.nlm.nih.gov/books/NBK1425/)
Clinical features: The clinical characteristics of MPGN and EDD are similar, cannot be distinguished based on clinical presentation. Both diseases predominantly affect children and young adults, although they can appear to any age. A common clinical manifestation is nephrotic syndrome (NS). Proteinuria is almost universally present. Sometimes is manifested as nephritic syndrome, with hematuria, edema, hypertension and proteinuria. Hematuria is very frequent and can be macrocospic and recurrent. In many cases there is elevation of the BUN and creatinine, which can, or no, return to normal values.
MPGN occasionally is asymptomatic and is detected in screening tests.
In both, MPGN and DDD, the disease is progressive, with a variable course and very few cases of complete remission. The time of evolution until terminal renal disease is very variable. It seems to have a worse prognosis for patients with NS. Some authors have found that persistent hypertension, serum creatinine increase at diagnosis, and macroscopic hematuria episodes are also related to worse prognosis.
There is no an effective treatment; there are schemes with immunosuppressors, nevertheless, the results are not consistent.
MPGN can recur after renal transplant. The percentage of recurrence is variable according to different authors, but it seems to be between 20% and 30%. DDD is the more post-transplant recurrent glomerular disease, practically in the 100% of cases; nevertheless the recurrence can be only as a morphologic finding, without producing damage of the graft (Appel GB, et al. J Am Soc Nephrol. 2005;16:1392-403. [PubMed link]; Braun MC, et al. J Am Soc Nephrol. 2005 ; 16:2225-33. [PubMed link] [Free full text]).
Laboratory findings: There are persistent low levels of C3 in MPGN and DDD, being more persistent in this last one. Low levels of C4 can be also demonstrated in MPGN, but C4 is usually normal in DDD. C3FeN is detected in most cases of DDD and in 25-50% of MPGN cases. Proteinuria, hematuria and alteration in the renal function tests are found as was expressed previously (see clinical features).
MPGN: There is a diffuse increase of tuft cellularity; the increase in cellularity is predominantly in the mesangial region, sometimes associated to abundant monocytes and neutrophils. “Lobulation” of the tuft can be prominent and capillary walls are thickened with decrease in capillary lumens.
Figure 1. Glomerulus increased of size, with mesangial hypercellularity and lobulated aspect; this appearance is very characteristic of membranoproliferative GN. The hypercellularity degree is variable among cases. See, in addition, a small epithelial crescent. This case corresponds to a 27-year-old woman with microscopic hematuria, proteinuria in nephrotic range, and BUN and serum creatinine increase; there was, in addition, moderate chronic tubule-interstitial changes (H&E, X400).
Figure 2. Just as in the Figure 1 there are tuft lobulation and mesangial hypercellularity, more accentuated in some areas (arrows). There is capillary lumen diminution (PAS, X400).
In capillaries, the walls are irregular and there is formation of double contours, the external portion of which is formed by the original GBM and the internal one by a new GBM-like material. Between both contours can be demonstrated some fuchsinophilic deposits (with trichrome stain) or interposed mesangial cells. Double contour can be circumferential or partial. In addition to mesangial cells, also can be “interposed” mononuclear inflammatory cells or endothelial cells.
Figure 3. The lobulations of the tuft are better seen with silver stains. With this stain the hypercellularity can not be well appreciated (Methenamine-silver, X300).
Figure 4. See the irregularities of the capillary walls with methenamine-silver stain. In some capillaries the lumen becomes imperceptible and in others they demonstrate clearly the double contours (arrows). Between the GBM and the “new GBM-like” there are immune deposits or “interposed” mesangial cells (Methenamine-silver, X400).
Figure 5. In this image we can see very well the irregular aspect of the capillary wall: the original GBM (green arrows), the neosynthesized GBM-like material in the internal aspect (blue arrows) and an interposed nucleus of mesangial cell (red arrow). The cytoplasm of the mesangial cell is located between both contours in a variable extension (Methenamine-silver, X1000).
Figure 6. In some cases it is possible to identify subendothelial deposits. In this case, with the trichrome stain, we can see those (fuchsinophilic: red) in the internal aspect of the capillary wall, demonstrating that they are subendothelial (arrows). These deposits can also be identified, in some cases, with methenamine-silver stain. Similar deposits, in the same location, can also be seen in other glomerular diseases due to immunocomplexes, more frequently lupus nephritis (Masson’s trichrome, X1000).
With disease progression the cellularity gradually diminishes and the acellular matrix increases, the tuft appear “solidified” and nodules with acellular center can be seen.
There are crescents in approximately 10% of patients and the percentage of glomeruli involved is variable among cases (Figure 1). This finding has been associated with a worse prognosis. In cryoglobulinemia is possible to find hyaline globules in capillary lumens.
Figure 7. The nodularity becomes very prominent in some cases. Notice the mesangial hypercellularity in the center of the nodules. This case corresponds to a case of cryoglobulinemia (see also Figure 8). (Masson’s trichrome, X400).
Figure 8. Same case of the previous microphotography. See the hypercellularity and diminution of capillary lumens, one of them completely occluded by a “hyaline thrombus” (arrow). Hyaline thrombi can be seen green, bluish or reddish depending on the technique used for the trichrome stain and, probably, on its composition (Masson’s trichrome, X1000).
The interstitium, tubules and vessels show unspecific changes that correlate with the severity of the chronic damage. Interstitial fibrosis and tubular atrophy are good indicators of the chronic renal damage and have good correlation with the prognosis, thus it is recommendable to carry out a semiquantitative or quantitative graduation of them.
DDD: The glomerular appearance is very variable, in some cases there are hypercellularity and lobulation, very similar to those of the MPGN, in other cases there are few glomerular changes, sometimes there is only mesangial hypercellularity, in other cases aspect of membranous GN (without “spikes”), and in others there is predominantly extracapillary proliferation. Necrotizing segments, segmental sclerosis, and polymorphous in the tuft can be also seen. The characteristic feature is the thickening of the GBM, with a rigid and eosinophilic aspect with the H&E staining. This thickening is due to heavy, PAS positive deposits, bluish or fuchsinophilic with trichrome staining, heavy blue with toluidine blue, they show a weak staining with silver stain. The deposits can be continuous or ribbon-like or periodically interrupted; the latter appearance has been likened to a “string of sausages”. The deposits are found in the GBM center and can appear surrounded by darker lines with the silver staining, forming double contours.
Similar deposits can be seen in the Bowman’s capsule and the basement membrane of the tubules, but they are more focal.
See case 65 of our case series: Dense deposit disease
See Case 158: Another DDD case.
Figure 9. In dense deposit disease the capillary walls appear rigid, thickened, and with a more intensely PAS stained center, also observed with trichrome (sometimes fuchsinophilic) (arrows). In some cases there is slight cellularity increase and in others it can be mesangial (as in this case) (Masson’s trichrome, X400).
Figure 10. Microphotography of a DDD case. See the notorious PAS-positive capillary walls thickening (arrows). (PAS stain, X400).
In MPGN there are C3, IgG and IgM deposits, being those of C3 more frequent and constant. These deposits are granular in the capillary walls. Often they are elongated and smooth in their external edge because they are subendothelial and they are molded to the GBM (Figure 11). IgA deposits are less frequent. In many cases there are also C4 and C1q deposition. Occasionally C3 deposits are predominantly mesangial.
Figure 11. Direct immunofluorescence for IgG in a case of type I MPGN. Ribbon-like subendothelial deposits with negativity in the mesangium, giving the appearance of lobes (X400).
In DDD the characteristic immunostaining is C3 irregularly distributed deposits throughout the capillary walls, with a smooth, granular or discontinuous pattern (Figure 12). It is accompanied by variable mesangial deposits. In some cases there are also mesangial deposits that look like large, coarse grains, sometimes with a central space: "mesangial rings" (Figure 13). There may also be C3 staining in the basal of some tubules and/or Bowman's capsule. In some cases C3 deposits are seen like two lines, surrounding a negative central zone (the dense deposit). It is not usual found deposits of other immunoglobulins, especially IgM.
Figure 12. Direct immunofluorescence for C3 in a case of dense deposits disease. Observe strong staining, like "ribbons", on capillary walls. This immunostaining is only for C3 (X400).
Figure 13. Direct immunofluorescence for C3 in a case of dense deposits disease. In addition to staining in glomerular capillary walls, there are coarse mesangial deposits: "mesangial rings", very characteristic of the disease, but not very usual, and deposits in basal membrane of some tubules (X400).
In MPGN electron-dense deposits between endothelial cells and GBM are demonstrated (Figure 14); in addition, there are mesangial deposits. “Interposition” refers to location of cytoplasmic processes of mesangial cells (or monocytes) between endothelium and GBM. The formation of “new basement membrane” is demonstrated under the endothelial cell (Figure 15). There is effacement of foot processes (podocytes) and occasional subepithelial small electron-dense deposits.
Figure 14. Subendothelial electron-dense deposits. In this case they proved to be positive for IgG and C3 (by immunofluorescence). ME X6,000. (Image courtesy of Dr. Carlos Jiménez).
Figure 15. Double contours in a case of type I MPGN. The blue arrows signal the original MBG, the red ones the neoformed, between both there are electron-dense deposits (immune complexes by IF). ME, X6,000. (Image courtesy of Dr. Carlos Jiménez).
In DDD the characteristic features is a layer of highly electron-dense material within the lamina densa of the GBM (Figure 16). These deposits can be linear and extensive or to be interrupted and irregular, with strands of normal-appearing GBM. Sometimes this material may be limited to paramesangial segments to the capillary loops. Some deposits of similar aspect are also observed in the mesangium. Deposits with the same ultrastructural features are observed in some tubular basement membranes and Bowman’s capsule.
Figure 16. Dense deposits occupying the MBG (blue arrows). The red asterisks indicate Bowman's space. ME, X8,000. (Image courtesy of Dr. Carlos Jiménez).
MPGN type III
This term has been used to designate two variants of type I: 1.) Burkholder’s type III variant: Membranoproliferative and membranous mixed GN, with all the features of type I and diffuse and global subepithelial deposits, with “spikes” that indicate a morphologic component of membranous GN (Burkholder PM, et al. Lab Invest 1970;23:459-479 [PubMed link]). The clinical characteristics and the course of these patients do not differ from those with MPGN type I, and the importance of making the distinction between this variant and type I MPGN is unclear.
2.) Strife’s type III variant (also called MPGN type III-Strife): MPGN similar to type I, with large subendothelial and subepithelial deposits that are connected to each other, extending through the GBM, with disruption of the lamina densa. There is also formation of “spikes” (Strife CF, et al. Clin Nephrol 1977;7:65-72 [PubMed link]). This variant is the one more widely accepted like MPGN type III. The presentation and clinical course usually do not differ to that of MPGN type I.
In MPGN type III-Strife C3NeF is usually no
detected, although complement activation seems also to be through the alternative
pathway, without activation of the classic pathway. This difference with type
I is that have allow to some authors to propose that it is a different disease.
Finally, images in “double contour”, that do not mean MPGN, can be demonstrated in some diseases nonassociated to immune complexes, like thrombotic microangiopathy and transplant glomerulopathy. In these cases a widening of the space between the GBM and the endothelium is demonstrated, with edema of the lamina rara interna and formation of new subendothelial GBM-like. There is no prominent hypercellularity.
A good revision of the theme in eMedicine:
P. Glomerulonephritis, Membranoproliferative.
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