Differences between membranoproliferative glomerulonephritis types I and III in clinical presentation, glomerular morphology, and complement perturbation

To interpret and analyze the changing patterns of histology and direct immunofluorescence findings in membranoproliferative glomerulonephritis

Background

Membranoproliferative glomerulonephritis has in the recent past been regrouped into immune complex-mediated (ICM MPGN) disease (driven by the classical complement pathway) and complement-mediated (C3GN) disease (driven by the alternative complement pathway) based on pathogenetic role of alternative complement pathway and immunofluorescence deposits. The proposed regrouping lent therapeutic and prognostic support in managing the disease of MPGN.

Aims and Objectives

The present study is undertaken to study the patterns of MPGN based on histopathological and DIF examination and sub-categorize the cases into mainly complement dominant and immune complex-mediated diseases for better prognostic and therapeutic utility.

Materials and Methods

This is a prospective observational study carried out in a tertiary care center over a period of 2 yrs. The clinically suspected cases of MPGN were subjected to histopathologic and direct immunofluorescence examination (DIF), and the findings were interpreted in light of complement-mediated and immune complex-mediated MPGN.

Results

Out of 620 renal biopsies, diagnosis of MPGN was confirmed both on histopathology and DIF in 36 cases accounting for 5.8% of all biopsies. Based on DIF findings, the various groups comprised 20 cases (55.6%) of immune complex deposits, 11 (30.5%) of C3 dominant picture, and 5 (13.9%) of Nil immune deposits. On analysis of the patterns on DIF, 16 cases (80%) of C3 + Ig group and 6 (54.5%) of C3GN group showed predominantly MPGN pattern. Crescentic glomerulonephritis, global glomerulosclerosis, and interstitial fibrosis were markedly observed in C3GN group.

Conclusion

DIF is of immense prognostic and therapeutic value in managing cases of MPGN.

Use of C4d as a diagnostic tool to classify membranoproliferative glomerulonephritis

BACKGROUND

Membranoproliferative glomerulonephritis (MPGN type I, II and III) was reclassified in 2013 as MPGN and C3 glomerulopathy (C3G) based on the complement system activation mechanism.

OBJECTIVES

To evaluate whether C4d, a component of the classical pathway, could be a diagnostic tool in differentiating between MPGN and C3G.

METHODS

We conducted a retrospective study of 15 MPGN type I, II and III and 13 minimal change disease (MCD) patients diagnosed between 2000 and 2012. C4d staining using the peroxidase method was employed.

RESULTS

Using the 2013 C3G consensus classification, the 15 MPGN types I, II and III biopsies were re-classified as MPGN (8) and C3G (7). Following C4d staining, of the 8 biopsies diagnosed as MPGN, 4 had classical pathway involvement [C1q (+), C3 (+), C4d (+)]; two had lectin pathway involvement [C1q (-), C3 (+), C4d (+)]; and, two were reclassified as C3G because the absence of C4d and C1q suggested the presence of the alternative pathway [C1q (-), C3 (+), C4d (-)]. Three of the seven C3G biopsies presented classical pathway involvement and were reclassified as MPGN. The alternative pathway was present in one of the other 4 biopsies considered to be C3G. Two C3G biopsies involved the lectin pathway and the one case of dense deposit disease had lectin pathway involvement.

CONCLUSIONS

C4d staining may help to differentiate between MPGN and C3G. In addition, the lectin pathway could play a role in the pathogenesis of these glomerulopathies.

Clinico-pathologic spectrum of C3 glomerulopathy-an Indian experience

Background

C3 glomerulopathy (C3GP) is characterized by deposition of complement C3 with absence/traces of immunoglobulins in the glomeruli and categorized into dense deposit disease (DDD), C3 glomerulonephritis (C3GN), complement factor H related protein 5(CFHR5) nephropathy etc. Collaborative efforts of pathologists, complement biologists and nephrologists worldwide are expanding the histomorphological pattern and laboratory findings related to C3GP. Hence, we studied point prevalence and morphological spectrum of C3GP in Indian patients to correlate morphological patterns with standard therapies and outcome of the patients.

Methods

Retrospective analysis of renal biopsies (2007-2012,n-4565), which on immunofluorescence (IF) had C3 dominant deposits with absence or trace amount of immunoglobulin was carried out. Histopathology and electronmicroscopy (EM) were reviewed; cases were re-classified as DDD and C3GN. Histomorphological patterns of both groups were compared and correlated with treatment. Clinical details and follow up of patients were retrieved from the department of nephrology.

Results

There were 31 cases (0.7%) of C3GP sub-classified as DDD (n-13) and C3GN (n-14). It was difficult to sub-classify 4 cases since EM showed overlapping features. C3GN and DDD had distinct clinical characteristics and disease outcome, though pathological features were overlapping. Majority of C3GP patients were males and were in 2^nd to 4^th decade of life. Nephrotic syndrome in DDD and nephritic-nephrotic presentation in C3GN patients was more common.

Hypertension and oliguria were more often observed in C3GN than DDD. Membranoproliferative pattern (MPGN) was commonest pattern in DDD; other patterns seen were mesangial proliferative, mesangial expansive/nodular, exudative and crescentic. C3GN also had all the above patterns, the predominant ones being MPGN and mesangial proliferative. Limited follow-up revealed response to therapy only in C3GN (33%). Progression to ESRD was 33% in DDD and 10% cases in C3GN.

Conclusion

C3GP comprise 0.7% of all renal biopsies. MPGN pattern was the commonest morphological pattern in DDD whereas MPGN and mesangial proliferative pattern were equally dominant patterns in C3GN. EM of 4 cases (13%) showed intermediate features. Evaluation of alternate complement pathway must be done in all cases to identify the point of dysregulated alternate complement pathway and to confirm the diagnosis in ambiguous cases.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1730070964135632

Kidney diseases caused by complement dysregulation: acquired, inherited, and still more to come

Inherited and acquired dysregulation of the complement alternative pathway plays an important role in multiple renal diseases. In recent years, the identification of disease-causing mutations and genetic variants in complement regulatory proteins has contributed significantly to our knowledge of the pathogenesis of complement associated glomerulopathies. In these diseases defective complement control leading to the deposition of activated complement products plays a key role. Consequently, complement-related glomerulopathies characterized by glomerular complement component 3 (C3) deposition in the absence of local immunoglobulin deposits are now collectively described by the term “C3 glomerulopathies.” Therapeutic strategies for reestablishing complement regulation by either complement blockade with the anti-C5 monoclonal antibody eculizumab or plasma substitution have been successful in several cases of C3 glomerulopathies. However, further elucidation of the underlying defects in the alternative complement pathway is awaited to develop pathogenesis-specific therapies.

Positive C1q staining associated with poor renal outcome in membranoproliferative glomerulonephritis

BACKGROUND

Pathogenesis and clinical prognosis of membranoproliferative glomerulonephritis (MPGN) has not yet been established.

METHODS

We conducted a retrospective study of 41 patients with MPGN (type I and III) and examined the renal survival. In addition, factors contributing to survival time were analyzed.

RESULTS

Fourteen patients (34 %) were classified into the renal death group. Patients with nephrotic syndrome and positive C1q staining of glomerular deposits showed a particularly poor prognosis. Significantly higher frequency of nephrotic syndrome and higher urinary protein excretion were observed in the renal death group (p = 0.0002, p = 0.0002) than in the renal survival group. The intensity of C1q staining was positively correlated with the severity of the proteinuria (p = 0.004). Factors that influenced the survival time were positive C1q staining of glomerular deposits (p = 0.003), presence of nephrotic syndrome (p = 0.004), serum albumin (p = 0.02), and proteinuria (p = 0.04).

CONCLUSIONS

C1q staining in glomerular deposits and nephrotic syndrome were important factors influencing the prognosis and outcome in MPGN patients. C1q deposition may play a key role in the pathogenesis of MPGN, as evidenced by numerous observations, such as induction of proteinuria.

Membranoproliferative glomerulonephritis and C3 glomerulopathy: resolving the confusion

Membranoproliferative glomerulonephritis (MPGN) denotes a general pattern of glomerular injury that is easily recognized by light microscopy. With additional studies, MPGN subgrouping is possible. For example, electron microscopy resolves differences in electron-dense deposition that are classically referred to as MPGN type I (MPGN I), MPGN II, and MPGN III, while immunofluorescence typically detects immunoglobulins in MPGN I and MPGN III but not in MPGN II. All three MPGN types stain positive for complement component 3 (C3). Subgrouping has led to unnecessary confusion, primarily because immunoglobulin-negative MPGN I and MPGN III are more common than once recognized. Together with MPGN II, which is now called dense deposit disease, immunoglobulin-negative, C3-positive glomerular diseases fall under the umbrella of C3 glomerulopathies (C3G). The evaluation of immunoglobulin-positive MPGN should focus on identifying the underlying trigger driving the chronic antigenemia or circulating immune complexes in order to begin disease-specific treatment. The evaluation of C3G, in contrast, should focus on the complement cascade, as dysregulation of the alternative pathway and terminal complement cascade underlies pathogenesis. Although there are no disease-specific treatments currently available for C3G, a better understanding of their pathogenesis would set the stage for the possible use of anti-complement drugs.

A hemolytic method for the measurement of nephritic factor

The absence of a simple and widely applicable test for the measurement of NF activity has hampered the accumulation of evidence bearing on its nephritogenicity. The extensive modification of a screening test for this autoantibody, reported here, has increased the range and precision of the test and made it less laborious. C3b deposited on sheep E by the reaction of NF with NHS forms a C5 convertase which, with addition of rat EDTA serum, leads to hemolysis of the cells proportionate under the right conditions to the concentration of NF in the reaction mixture. The calibration line is straight or slightly concave and passes through the origin. The method detects the activity of both the NF of the amplification loop, NFa, found in MPGN type II, and the NF of the terminal pathway, NFt, found in MPGN types I and III. Interday coefficients of variation ranged from 6.6% to 13.5% and intraday from 7.0% to 12.6%. Although serum C3 levels can be markedly depressed when NF levels are high, C3 levels and NF activity generally correlate poorly. The C3 level could be low and NF absent or, occasionally, NF present with the C3 level normal. NF activity was absent from the stored serum of patients with active SLE, AGN or with an IgA nephropathy.

MPGN II--genetically determined by defective complement regulation?

MPGN II is a rare disease which is characterized by complement containing deposits within the GBM. The disease is characterized by functional impairment of the GBM causing progressive loss of renal function eventually resulting in end stage renal disease. It now becomes evident that in addition to C3NeF, which inhibits the inactivation of the alternative C3 convertase C3bBb, different genetically determined factors are also involved in the pathogenesis of MPGN II. These factors though different from C3NeF also result in defective complement regulation acting either through separate pathways or synergistically with C3NeF. Following the finding of MPGN II in Factor H deficient animals, patients with MPGN II were identified presenting with an activated complement system caused by Factor H deficiency. Factor H gene mutations result in a lack of plasma Factor H or in a functional defect of Factor H protein. Loss of Factor H function can also be caused by inactivating Factor H autoantibodies, C3 mutations preventing interaction between C3 and Factor H, or autoantibodies against C3. Identification of patients with MPGN II caused by defective complement control may allow treatment by replacement of the missing factor via plasma infusion, thus possibly preventing or at least delaying disease progress.

A mechanism for the development of subepithelial deposits in a patient with type III membranoproliferative glomerulonephritis

We report on a patient with membranoproliferative glomerulonephritis (MPGN) type III, whose repeated renal biopsies show evolution from a type I-like pattern to a type III pattern of immune complex formation over a 1-year period. Based on the development of experimental in situ immune complex glomerulonephritis, we discuss possible mechanisms for the formation of subepithelial deposits in type III MPGN with reference to an experimental in situ immune complex model of glomerulonephritis.

Linkage of a gene causing familial membranoproliferative glomerulonephritis type III to chromosome 1

Membranoproliferative glomerulonephritis (MPGN) type III is a chronic progressive renal disease of unknown cause. The diagnosis is based on renal pathologic features (specifically immunofluorescence staining patterns and ultrastructural appearance). Mesangial cell proliferation and subendothelial and subepithelial deposits characterize the renal disease. Although the actual prevalence of this disease is not known, the disease is rare and usually sporadic. The clinical features of MPGN include the nephrotic syndrome and hematuria, with renal dysfunction occurring in approximately 50% of patients. Progression to end-stage renal disease is variable, and some patients exhibit stabilization or even improvement. Here is presented an Irish family in which there are eight affected members in four generations, suggesting autosomal dominant inheritance. This is the only reported family with an inherited form of MPGN type III. To evaluate the disease in this family, a genome-wide scan was performed with a panel of 402 polymorphic microsatellite markers, defining a grid with an average resolution of 10 cM (centimorgans). Significant evidence for linkage was observed on chromosome 1q31-32, with a maximal logarithm of the odds score of 3.86 at theta = 0.00 for microsatellite marker GATA135F02. Recombination events among affected individuals, as detected by haplotype analysis, established a 22-cM minimal candidate region flanked by markers D1S3470 and GATA124F08. The data provide evidence for a gene for familial MPGN on chromosome 1q.

Membranoproliferative glomerulonephritis in association with chronic lymphocytic leukaemia: a report of three cases

AIMS

The reported association of glomerular disease with chronic lymphocytic leukaemia (CLL) is rare despite the relative frequency of this type of leukaemia. Hence, we have examined the renal biopsies in three patients with CLL and glomerulonephritis.

METHODS

Renal biopsies were examined by light microscopy, immunofluorescence microscopy and electron microscopy.

RESULTS

One of two patients with mild impairment of renal function and an active urinary sediment had ultrastructural features of idiopathic type I membranoproliferative glomerulonephritis (MPGN), and the other had features of fibrillary/ immunotactoid glomerulonephritis with deposits of IgG and C3. One patient with nephrotic syndrome had characteristic electron microscopic appearances of type III MPGN. In all three there was an association with monoclonal gammopathy. The parameters of glomerular damage improved in association with response to drug treatment of the CLL.

CONCLUSION

There is a spectrum of types of MPGN seen in patients with CLL and there appears to be an association with the presence of monoclonal gammopathy. This is the first reported case of type III MPGN in CLL.

Complement analysis in children with idiopathic membranoproliferative glomerulonephritis: a long-term follow-up

Fifty children with idiopathic membranoproliferative glomerulonephritis (MPGN), aged 2-14 years at apparent onset, were monitored for the presence of C3 nephritic factor (C3 NeF) and signs of complement activation in serum. In addition, C3 allotyping was performed in 32 patients. Observation time ranged from 2 to 20 (median 11) years. C3 NeF activity was detected at least once in 60% of the patients (in 11 of 26 with type I, in 15 of 17 with type II, and in four of seven with type III). C3 NeF-positive patients had significantly reduced levels of CH50 and C3 and elevated levels of C3dg/C3d. During follow-up, C3 levels were persistently normal in 62% of the patients with MPGN type I and in 43% with type III but in only 18% with type II. C3 allotype frequencies differed from those found in healthy controls with a significant shift to the C3F/C3FS variants in C3 NeF-positive patients. C3b(Bb)P as a marker for alternative pathway activation was not increased in C3 NeF-positive patients. Despite the presence of C3 NeF activity, C3 levels remained normal in six patients throughout the observation period. C3 NeF became undetectable in six patients, whereas seven developed C3 NeF activity during follow-up. There was no significant difference in renal survival probability in patients with or without C3 NeF activity. Neither C3 variants nor continuous low C3 or low CH50 levels had any prognostic value for the clinical outcome. No factor H deficiency was detected.

Differences between membranoproliferative glomerulonephritis types I and III in long-term response to an alternate-day prednisone regimen

Membranoproliferative glomerulonephritis (MPGN) is classified as type I, II, or III based on ultrastructural alterations in the glomerular basement membrane. Whereas type II has long been recognized as clinically and pathologically unique, types I and III are often difficult to distinguish and have not been separated in most clinical studies. We compared the course and long-term outcome of patients with types I and III MPGN followed up at this institution since 1960. During this period, 21 patients with type I and 25 patients with type III were followed up for a minimum of 5 years. Patients with types I and III MPGN did not differ in age at apparent onset, age at diagnosis, or interval from apparent onset of symptoms to diagnosis (biopsy). They had similar initial serum C3 and serum albumin levels. Patients with type I had a significantly lower initial mean estimated glomerular filtration rate (GFR(est)) compared with those with type III (99.1 +/- 35.9 versus 131.6 +/- 36. 1 mL/min/1.73 m(2); P < 0.01). Type and duration of therapy, length of follow-up, and frequency of complications of therapy did not differ between groups. There was, however, a significant difference in duration of hypocomplementemia. After 1 year of an alternate-day prednisone regimen, 90% of the type I patients normalized their serum C3 levels compared with less than 50% of type III patients (P < 0.01). After 3 years of therapy, only 5% of type I patients were hypocomplementemic compared with 33% of type III patients (P < 0.02). In addition, disease relapse occurred in six type III patients (24%) compared with no type I patients. At last follow-up, type I patients had a slight improvement in mean GFR(est) (+6.3 +/- 48.4 mL/min/1.73 m(2)), whereas type III patients had a 25% decrease in mean GFR(est) (-34.8 +/- 47.6 mL/min/1.73 m(2); P < 0.01). Residual urinary abnormalities were significantly more frequent in patients with type III than type I MPGN. Hematuria persisted in 72% versus 38% (P < 0.05) and proteinuria in 28% versus 0% (P < 0.01) of those with types III and I, respectively. These results give clear evidence of significant differences in the clinical progression of the two types and their response to the alternate-day prednisone regimen. Whereas the outcome of patients with type I MPGN treated with alternate-day prednisone was generally good, similarly treated patients with type III experienced significant reductions in renal function, slower improvement in serum C3 levels, more persistent urinary abnormalities, and more frequent relapses.

Partial lipodystrophy, mesangiocapillary glomerulonephritis, and complement dysregulation. An autoimmune phenomenon

Partial lypodistrophy (PLD) is a rare disease in which, there is loss of fat usually from the upper part of the body. The disease is frequently associated with mesangiocapillary (membranoproliferative) glomerulonephritis Type II (MCGN II). In the early 1970s, it was noticed that MCGN II and/or PLD was sometimes associated with dysfunction of the complement system as reported in several case descriptions and studies. Subsequently, an IgG autoantibody was detected-C3 nephritic factor (C3NeF). The target of this autoantibody is the alternative pathway C3 convertase-C3bBb. There are sporadic case reports that linked PLD, MCGNII, and C3NeF with autoimmune diseases. This association may be more than a coincidence. The complement deficiency may lead to perturbation of the immune system, which may trigger some of the autoimmune diseases. This article will be focused on the association among PLD, MCGN II and C3NeF.

In situ complement activation in porcine membranoproliferative glomerulonephritis type II

Pigs genetically deficient in complement factor H all develop lethal membranoproliferative glomerulonephritis (MPGN) type II characterized by massive glomerular deposits of complement, intramembranous dense deposits, and mesangial hypercellularity. To elucidate the chronological relationship between these glomerular changes, and to precisely determine the localization of glomerular complement deposits, we studied kidney specimens from factor H-deficient piglets at different ages from fetal life until terminal kidney failure had developed. Deposits of C3 and the terminal complement complex localized within the glomerular basement membrane (GBM) were present already in factor H-deficient fetuses, without concurrent intramembranous dense deposits or mesangial hypercellularity. Incipient subendothelial dense deposits containing complement appeared no earlier than four days after birth, and intramembranous dense deposits in older piglets with established MPGN type II also contained large amounts of complement as detected by immune electron microscopy. Onset of kidney failure coincided with pronounced mesangial hypercellularity and expansion, compromising glomerular capillary patency. Formation of glomerular capillary wall double contours coincided with electron microscopic evidence of laminar disintegration of intramembranous dense deposits. Complement was also deposited in the mesangial matrix, but not on glomerular cells. We conclude that all components of the alternative and terminal pathways of complement have access into the GBM and the mesangial matrix. In the absence of factor H, complement is spontaneously activated and deposited in situ in these locations resulting in dense deposit formation. It is proposed that factor H dysfunction may play an essential role even in human MPGN type II.

Recurrent type III membranoproliferative glomerulonephritis after kidney transplantation

The first well-documented case of recurrent type III membranoproliferative glomerulonephritis after kidney transplantation is reported in this article. A 48-year-old man was admitted to the hospital because of nephrotic syndrome and moderate renal failure. The renal biopsy showed double-contour images at light microscopy. Electron microscopy revealed electron-dense deposits in the mesangium and in both the subepithelial and subendothelial sides of the basement membrane. Subepithelial deposits were sometimes hump-like and produced an irregular disruption of the lamina densa. A diagnosis of type III membranoproliferative glomerulonephritis was suggested. The patient had a rapid decrease in renal function and received dialysis in 3 months. Three years later, he received a cadaveric kidney transplant, and subsequently recovered normal renal function. Proteinuria appeared after 13 months, and a biopsy of the graft demonstrated recurrence of the original disease. Seven years after transplantation, he returned to hemodialysis.

Discordant renal histopathologic findings and complement profiles in membranoproliferative glomerulonephritis type III

Patients with membranoproliferative glomerulonephritis (MPGN) type III and a low serum C3 concentration tend to have evidence for a nephritic factor of the terminal complement pathway (Nft). Complement profiles were studied in three patients with MPGN type III and low serum C3 concentrations. Serum C3 concentrations were 52, 21, and 14 mg/dL (normal range, 83 to 177 mg/dL). Serum Clq, C2, C4, properdin, and C5 concentrations were normal in all patients, whereas two had a slight decrease of C7 or C8. This pattern of complement activation resembles that seen with MPGN type II in which a nephritic factor activates the amplification loop (NFa). We conclude that in patients with MPGN type III the previously reported profile/presence of Nft is not always found, at least in the chronic stage of the disease, despite a low C3 value.

Chronic glomerulonephritis in childhood. Membranoproliferative glomerulonephritis, Henoch-Schönlein purpura nephritis, and IgA nephropathy

The chronic glomerulonephritides that lead to permanent loss of renal function may present with an acute nephritic syndrome, nephrotic syndrome, or asymptomatic hematuria and proteinuria. Membranoproliferative glomerulonephritis, Henoch-Schönlein purpura nephritis, and IgA nephropathy are common childhood glomerulonephritides that may lead to chronic renal failure. Their clinical manifestations, natural history, and long-term prognosis are distinct. This article reviews various presentations of these common childhood glomerulonephritides and an approach to management and potential therapy.

Participation of CR1 (CD35), CR3 (CD11b/CD18) and CR4 (CD11c/CD18) in membranoproliferative glomerulonephritis type I

Intraglomerular expression of complement receptors (CR) was investigated chronologically in 22 repeatedly biopsied patients with membranoproliferative glomerulonephritis (MPGN) type I by indirect immunoperoxidase staining using MoAbs. Patients were divided into two groups based on whether intraglomerular C3c deposition was decreased at the second biopsy (2nd Bx) (group A, n = 12), or not (group B, n = 10). At the first biopsy (1st Bx), the severity of glomerular injury and the degree of glomerular C3c deposition were compatible between the two groups. Four patterns of CR1 (CD35) expression on podocytes were recognized: normal; generally decreased; focally/segmentally lost; and completely lost. The numbers of CR3 (CD11b/CD18)- and CR4 (CD11c/CD18)-positive cells per glomerular cross-section were counted. At the 1st Bx, no significant difference was found in the number of CR3+ or CR4+ cells between the two groups. At the 2nd Bx, the numbers of both the CR3+ and CR4+ cells were significantly decreased only in group A (P < 0.01). The numbers of CR3+ and CR4+ cells were significantly higher in cases with moderate or marked C3c deposits than in those with no or mild C3c deposits. The intensity of CR1 expression in group B was less than that in group A at both the 1st and 2nd Bx (1st, P < 0.05; 2nd, P < 0.01), and chronological improvement of CR1 expression was observed only in group A. The severity of glomerular injury was increased only in group B (P < 0.01), and was associated with persistent massive proteinuria and hypocomplementaemia. Our results suggest that, in cases with an adverse outcome, a more severe defect of CR1 initially exists and the expression of CR1 is not recoverable chronologically. This irreversible decrease or loss of CR1 may partly contribute to the continuous C3c deposition and intraglomerular infiltration of CR3+ and CR4+ cells.

Hereditary porcine membranoproliferative glomerulonephritis type II is caused by factor H deficiency

We have recently described hereditary membranoproliferative glomerulonephritis type II in the pig. All affected animals had excessive complement activation, revealed as low plasma C3, elevated plasma terminal complement complex, and massive deposits of complement in the renal glomeruli, and eventually died of renal failure within 11 wk of birth. The aim of the present study was to investigate the cause of complement activation in this disease. Transfusion of normal porcine plasma to affected piglets inhibited complement activation and increased survival. Plasma was successively fractionated and the complement inhibitory effect of each fraction tested in vivo. A single chain 150-kD protein which showed the same complement inhibitory effect as whole plasma was finally isolated. Immunologic cross-reactivity, functional properties, and NH2-terminal sequence identified the protein as factor H. By Western blotting and enzyme immunoassay, membranoproliferative glomerulonephritis-affected piglets were demonstrated to be subtotally deficient in factor H. At 1 wk of age, median (range) factor H concentration was 1.6 mg/liter (1.1-2.3) in deficient animals (n = 13) and 51 mg/liter (26-98) in healthy littermates (n = 52). Our data show that hereditary porcine membrano-proliferative glomerulonephritis type II is caused by factor H deficiency.

Nephritic factors predispose to chronic glomerulonephritis

Chronic glomerulonephritis has been reported in three rare conditions in which factor H of the complement system does not function normally. Factor H is essential for the inactivation of the C3b-dependent convertase, C3b,Bb, which is constantly being formed in vivo. With factor H dysfunction, this convertase accumulates and produces hypocomplementemia. Twenty-two individuals have been reported with the three forms of H dysfunction, and 12 have displayed evidence of chronic glomerulonephritis. In addition, matings of certain Yorkshire pigs result in offspring that are homozygous deficient in factor H and have a high incidence of a severe hypocomplementemic glomerulonephritis closely resembling membranoproliferative glomerulonephritis type II. The hypothesis proposed is that the nephritis that develops with these forms of H dysfunction is in some way the result of circulating convertase. The corollary is that nephritic factors, also producing H dysfunction and higher than normal circulating levels of the C3b-dependent convertase, are responsible for the glomerulonephritides with which they are associated, mainly membranoproliferative glomerulonephritis types II and III. Nephritic factors are autoantibodies that bind to the C3b-dependent convertase and render it resistant to dissociation by factor H. Although nephritic factors are currently considered epiphenomena, their role in the pathogenesis of membranoproliferative glomerulonephritis should be reconsidered based on the evidence that circulating convertase is nephritogenic.

Activated C3 (C3b) in the nephritic glomerulus

An autoradiographic technique was developed to assess in the nephritic glomerulus the relative amount of C3 which is in the activated form, C3b, compared with the inactivated form, iC3b. Frozen renal biopsy sections from children and young adults with glomerulonephritis were assessed for the C3b fraction of total C3, using a radiolabeled monoclonal anti-C3c. Grain counts with this antibody, before and after reacting the section with 0.0002% trypsin, gave the relative amounts of total C3 and C3b, respectively. C3b was found in all diseases studied. To explain its presence, glomerular C3b acceptors which would restrict C3b inactivation were sought by immunofluorescence studies. C3b acceptor candidates were: IgG in aggregated form, IgA as found in the IgA nephropathies and the C3/C5 convertase, C4b,2a,3b. In acute post-streptococcal glomerulonephritis and membranoproliferative glomerulonephritis type III, diseases in which these acceptors were lacking, it is postulated that the nephritis strain-associated protein and absence of membrane cofactor protein, respectively, may be responsible for C3b deposition. The phlogistic effect of C3b is mediated largely by one of its products, C5b-9. However, the C3b: total C3 ratio failed to correlate with indices of glomerular inflammation, probably in part because the ratio is not a measure of total glomerular C3b.

Long-term follow-up of non-systemic lupus erythematosus glomerulonephritis in patients with hereditary angioedema: report of four cases

Hereditary angioedema (HAE) is characterized by a deficiency in C1 inhibitor protein (C1 INH) and by clinical symptoms of episodic swelling of subcutaneous or mucosal tissue. It has rarely been reported in association with non-systemic lupus erythematosus (SLE) glomerulonephritis (GN). A recent report of two cases indicates the prognosis to be poor, with both patients progressing to chronic renal failure 8 and 20 years after diagnosis. This report describes the 5-year follow-up of a previously unreported case of an 8-year-old boy with HAE and non-SLE membranoproliferative glomerulonephritis (MPGN). The patient developed macroscopic hematuria, azotemia, and a vasculitic rash. Treatment included prednisone and cyclophosphamide, resulting in clinical improvement. The present report also summarizes the long-term follow-up of three previously reported cases of HAE and non-SLE GN, 25, 16, and 10 years after their initial presentation. Patients monitored for 25 and 16 years had MPGN and normal renal function and received no therapy. The third patient, monitored for 10 years, had segmental MPGN. This patient presented with urinary abnormalities and, after treatment with prednisone, had improvement in her hematuria. None of these four patients developed chronic renal failure. These observations indicate a variable outcome in patients with HAE and non-SLE GN.

IgG subclass restriction of autoantibody to solid-phase C1q in membranoproliferative and lupus glomerulonephritis

The IgG subclass distribution for autoantibodies to solid-phase C1q (anti-spC1q) in sera from 14 patients with membranoproliferative glomerulonephritis (MPGN) and 10 patients with systemic lupus erythematosus (SLE) nephritis was determined by an enzyme-linked immunosorbant assay employing C1q as the immunosorbant in the presence of 2 M NaCl to prevent Fc binding and monoclonal anti-human IgG subclass reagents. The autoantibody to spC1q in MPGN, especially in types I (7 patients) and II (3 patients), was almost entirely restricted to IgG3. In contrast, in SLE anti-spC1q was completely restricted to IgG2 in 3 patients while predominantly IgG2 in the other 7 patients. The different subclass restriction of anti-spC1q in these two disorders suggests that antibody formation is either in response to different epitopes on the collagen-like region of C1q or that patients with SLE and MPGN mount different immunologic responses to the same antigenic stimulus.

Treatment of mesangiocapillary glomerulonephritis with alternate-day prednisone--a report of the International Study of Kidney Disease in Children

It has been claimed that long-term prednisone treatment ameliorates the course of children with mesangiocapillary glomerulonephritis (MCGN). The International Study of Kidney Disease in Children conducted a randomized, double-blinded, placebo-controlled clinical trial in 80 children with idiopathic MCGN, including 42 patients with type I disease, 14 with type II disease, 17 with type III disease, and 7 with nontypable disease. Criteria for admission included heavy proteinuria and a glomerular filtration rate of greater than or equal to 70 ml/min per 1.73 m2. Prednisone or lactose, 40 mg/m2, was given every other day as a single morning dose. The mean duration of treatment was 41 months, renal failure being the most common reason for termination of therapy. Treatment failure was defined as an increase from baseline of 30% or more in serum creatinine, or more than 35 mumol/l. Overall, treatment failure occurred in 55% of patients treated with lactose, compared with 40% in the prednisone group. Life-table analysis showed a renal survival rate (i.e., stable renal function) at 130 months of 61% among patients receiving prednisone and 12% among patients receiving lactose (P = 0.07). Of patients with type I or III MCGN, 33% treated with prednisone were treatment failures, compared with 58% in the lactose group. Long-term treatment with prednisone appears to improve the outcome of children with MCGN.

Idiopathic membranoproliferative glomerulonephritis in childhood

Membranoproliferative glomerulonephritis (MPGN), recognized since 1965, is now known to have three forms, designated types I, II, and III. The types are similar in the frequency of hypocomplementemia and clinical course but are dissimilar in glomerular ultrastructure, pathogenesis, mechanisms of complement activation, predisposition to recur in the renal transplant, and, to some extent, in clinical presentation. Although glomerular proliferation is usually diffuse, it may be focal and segmental particularly in mild cases of MPGN I. Hypocomplementemia, present in about 80% of patients, is the result of hypercatabolism of C3 by three mechanisms as well as of diminished C3 synthesis. The hypocomplementemia is unrelated to clinical course or prognosis. Although MPGN I and III both have a high frequency of an extended haplotype on chromosome 6, which has known associations with autoimmune phenomena, and both have a high frequency of inherited complement defects, they are nevertheless dissimilar in glomerular ultrastructure, complement profile, and immunohistology in ways which suggest a wide difference in pathogenesis. Abnormalities in humoral immunity appear not to be involved in MPGN III. Treatment with anticoagulant, antiplatelet and cytotoxic drugs have, in controlled trials, been either ineffective or marginally effective. Long-term use of alternate-day prednisone in high dosage appears to be the most efficacious regimen in both controlled and uncontrolled studies.

Patterns of complement activation in idiopathic membranoproliferative glomerulonephritis, types I, II, and III

Complement profiles on 22 hypocomplementemic patients with membranoproliferative glomerulonephritis (MPGN) type I, on 11 with MPGN II, and on 16 with MPGN III, gave evidence that the nephritic factor of the amplification loop (NFa) is responsible for the hypocomplementemia in MPGN II and the nephritic factor of the terminal pathway (NFt) for the hypocomplementemia in MPGN III. In contrast, in MPGN I, there was evidence for three complement-activating modalities, NFa, NFt, and immune complexes. As a result, four different patterns of complement activation were seen. NFa, found in MPGN II, produces a complement profile characterized mainly by C3 depression. In addition, four of seven (57%) severely hypocomplementemic MPGN II patients (C3 less than 30 mg/dL) had slightly depressed levels of factor B, and one of seven (14%) of properdin, but in all the C5 concentration was normal. In contrast, all eight severely hypocomplementemic patients with MPGN II had depressed C5 and properdin levels, and six of eight (75%) depressed levels of C6, C7, and/or C9. Of eight MPGN III patients with moderate hypocomplementemia, 50% had depressed C5 and properdin levels and the remainder, depressed C3 only. This spectrum of profiles is most likely produced by varying concentrations of NFt. In MPGN I, nine of 23 (39%) had a profile indicating only classical pathway activation; seven of 23 (39%), a pattern compatible with NFt alone; four of 23 (9%), evidence for both classical pathway activation and NFt; and three of 23 (13%), a pattern compatible with NFa. The unique multifactorial origin of the hypocomplementemia in MPGN I, often giving evidence of classical pathway activation, together with previously reported differences in glomerular morphology and clinical features at onset, makes it distinct from MPGN III. Depressed C8 levels were found to some extent in all hypocomplementemic states. The levels were uncommonly depressed in patients with NFa, most markedly depressed with NFt, and moderately reduced with classical pathway activation. The cause is not known. Diagnostically, profiles showing classical pathway activation and low levels of C6, C7, and/or C9 are specific for MPGN I. Those showing only classical activation are likewise diagnostic of MPGN I if systemic lupus erythematosus (SLE) and chronic bacteremia are ruled out.

Autoantibody to complement neoantigens in membranoproliferative glomerulonephritis

With the exception of C3 nephritic factor, autoantibody formation has not been commonly associated with membranoproliferative nephritis (MPGN). We measured autoantibodies (nephritic factors) to the C3 convertases C3bBb (NFa) and C3bBbP (NFt), which result in fast and slow C3 activation, respectively, and to a neoantigen on C1q fixed to a solid phase (spC1q) in sera from 29 patients with MPGN type I, 26 with type II, and 28 with type III. Autoantibody formation was common in all MPGN types. An autoantibody to a C3 convertase neoantigen was identified in more than 75% of the hypocomplementemic MPGN sera tested. Anti-C3bBb (NFa) was present in 81% of patients with MPGN type II but was rarely found in either type I or type III. Anti-C3bBbP (NFt) was common in both MPGN I and III. Anti-spC1q was present in 74% of patients with type I and in 38% and 48% of types II and III MPGN, respectively. Patients with MPGN types I, II, and III had one and two serum autoantibodies detected significantly more frequently than did a group of healthy subjects. The presence of any one autoantibody was not specifically associated with the presence of any other autoantibody. The results indicate that multiple autoantibody formation is common in all MPGN types. MPGN II, and possibly MPGN I, tend to form more specific autoantibodies.

A properdin dependent nephritic factor slowly activating C3, C5, and C9 in membranoproliferative glomerulonephritis, types I and III

The IgG fraction of serum from patients with membranoproliferative glomerulonephritis (MPGN) types I and III was found to contain a nephritic factor (NFI/III) which differed from that usually present in MPGN type II and partial lipodystrophy (NFII) in that it converts C5 and C9 as well as C3, is dependent on properdin for its activity, and requires an incubation period of several hours rather than 30 min for its demonstration. C3 conversion occurred in the absence of an intact classical pathway. This nephritic factor was found in patients with reduced serum levels of terminal components and its activity, like that of the nephritic factor in MPGN type II, correlated with the serum C3 level indicating that these nephritic factors play a large role in producing hypocomplementemia. Although potentially nephritogenic because of its ability to activate the terminal pathway, the presence of this nephritic factor did not clearly correlate with clinical course.

Serum terminal complement component levels in hypocomplementemic glomerulonephritides

Measurements of serum C3 through C9 are reported for patients with acute poststreptococcal glomerulonephritis (AGN), membranoproliferative glomerulonephritis type I (MPGN I), MPGN II, and MPGN III. Except in MPGN II, depressed C5 levels correlated with depressed C3 levels. In MPGN II, levels of C5 and of other terminal components were normal. In MPGN III, markedly depressed levels of C7 through C9 correlated strongly with depressed levels of C3 and C5. C6 was less severely depressed. In MPGN I, terminal component levels were less often depressed than in MPGN III and in AGN, depression of terminal components was seen only when levels of C3 and C5 were extremely low. The data indicate that late terminal components are activated in MPGN III to a greater extent than in the other nephritides despite C5 activation approximately equal in extent to that in AGN and MPGN I.

Antibody to a cryptic, solid phase C1Q antigen in membranoproliferative nephritis

IgG containing material detected in membranoproliferative nephritis (MPGN) serum with a solid phase (sp) Clq ELISA has been presumed to be immune complexes. However, in serum from 13 MPGN patients containing large amounts of spClq-binding material, sucrose density ultracentrifugation and sieve chromatography showed spClq-binding protein to sediment at 7S or cofractionate with IgG. One serum (stored for 12 years) contained, in addition, spClq-binding material sedimenting at more than 19S. Isolated MPGN IgG was shown to bind to spClq. SpClq-binding material could be totally removed from MPGN serum by absorption with BSA-anti-BSA immune precipitates, and by acid elution of the precipitates IgG binding to spClq could be recovered. F(ab')2, isolated from pepsin digested MPGN IgG, continued to bind spClq. Binding of MPGN IgG or F(ab')2 to spClq was not inhibited by 2 M NaCl. Incubation of MPGN serum with 125I Clq followed by sucrose density ultracentrifugation resulted in a peak of radioactivity at 11S, the sedimentation rate of Clq, giving evidence that material binding fluid phase Clq is not present. SpClq-binding IgG was detected in 54% of 68 MPGN patients. These results indicate that the 7S spClq-binding IgG represents antibody to a cryptic antigen revealed only when Clq fixes to a solid surface.