Membranous glomerulonephritis,antiphospholipid syndrome,and persistent low C3 levels associated with meningococcal disease

A young male patient with a recent history of meningococcemia was referred to our hospital in his recovery period. He had signs suggesting deep venous thrombosis in the legs but no other abnormalities on physical examination at admission. Laboratory results showed proteinuria (3.1 g/day), prolonged activated partial thromboplastin time (56.3 s), low level of C3c (0.19 g/l), high titers of both IgM (27.04 MPLU/ml) and IgG (74.88 GPLU/ml) anticardiolipin antibodies and recanalized thrombotic changes in the deep veins of the lower extremities on venography. Histopathological diagnosis of the kidney disease was membranous glomerulonephritis. He was started on an angiotensin-converting enzyme inhibitor to reduce proteinuria and an oral anticoagulant to prevent thromboembolic events. Since no reduction in proteinuria was observed at the 10th month of therapy, the angiotensin-converting enzyme inhibitor was discontinued. On his last follow-up, approximately 1.5 years after meningococcemia, he had no complaints and no abnormal findings on physical examination. While both IgM and IgG anticardiolipin antibody titers returned to the normal range, he still had persistent proteinuria and hypocomplementemia.     

Validation of a Histologic Scoring Index for C3 Glomerulopathy

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Humanized C3 Mouse: A Novel Accelerated Model of C3 Glomerulopathy

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Eculizumab and recurrent C3 glomerulonephritis

Background

Hyperactivity of the alternative complement pathway is the principle defect in C3 glomerulopathies (C3G). Eculizumab, a monoclonal antibody that binds C5 to prevent formation of the membrane attack complex, has been shown to be beneficial in some patients with this disease.

Methods

In this open-label, proof-of-concept efficacy-and-safety study, a patient with the initial diagnosis of dense deposit disease (DDD) and allograft recurrence of C3 glomerulonephritis (C3GN) was treated with eculizumab every other week for 1 year. The patient had pathological evidence of C3GN and proteinuria >1 g/day at enrollment. He underwent graft biopsy before enrollment and repeat biopsy at 6 and 12 months.

Results

Although no mutations were identified in complement genes, functional studies were positive for C3 nephritic factors and elevated levels of soluble membrane attack complex (sMAC). On therapy, sMAC levels normalized and although proteinuria initially decreased, it increased reaching pre-treatment levels at 12 months. Although serum creatinine remained stable, repeat allograft biopsies showed progression of disease.

Conclusions

Clinical and histopathologic data suggest a partial response to eculizumab in this patient. While eculizumab blocked activation of the terminal complement cascade, persistent dysregulation of the alternative pathway remained, indicating eculizumab alone cannot control disease in this patient. Additional research is required to identify effective anticomplement therapy for this group of C3G patients.     

Efficacy of Targeted Complement Inhibition in Experimental C3 Glomerulopathy

C3 glomerulopathy refers to renal disorders characterized by abnormal accumulation of C3 within the kidney, commonly along the glomerular basement membrane (GBM). C3 glomerulopathy is associated with complement alternative pathway dysregulation, which includes functional defects in complement regulator factor H (FH). There is no effective treatment for C3 glomerulopathy. We investigated the efficacy of a recombinant mouse protein composed of domains from complement receptor 2 (CR2) and FH (CR2-FH) in two models of C3 glomerulopathy with either preexisting or triggered C3 deposition along the GBM. FH-deficient mice spontaneously develop renal pathology associated with abnormal C3 accumulation along the GBM and secondary plasma C3 deficiency. CR2-FH partially restored plasma C3 levels in FH-deficient mice 2 hours after intravenous injection. CR2-FH specifically targeted glomerular C3 deposits, reduced the linear C3 reactivity assessed with anti-C3 and anti-C3b/iC3b/C3c antibodies, and prevented further spontaneous accumulation of C3 fragments along the GBM. Reduction in glomerular C3d and C9/C5b-9 reactivity was observed after daily administration of CR2-FH for 1 week. In a second mouse model with combined deficiency of FH and complement factor I, CR2-FH prevented de novo C3 deposition along the GBM. These data show that CR2-FH protects the GBM from both spontaneous and triggered C3 deposition in vivo and indicate that this approach should be tested in C3 glomerulopathy.     

C3 nephritic factor and mesangiocapillary glomerulonephritis

The association of a C3 splitting activity, known as C3 nephritic factor (C3NeF), with mesangiocapillary glomerulonephritis (MCGN), especially MCGN type II, has long been known. Several forms of C3NeF are now recognised, the main one being an IgG which acts as an autoantibody binding to factor H, a normally occurring component of the complement system. Complement is in a continuous state of activation with inbuilt checks and controls, and factor H plays a very important part in the controlling mechanisms by preventing the overwhelming activation of complement at the stage of C3 conversion. C3NeF binds to factor H, thus preventing its inhibitory action, and allowing complement activation to proceed with, in vivo, the well-known consequences in MCGN of very low serum levels of C3. The question naturally arose whether C3NeF causes MCGN. Complex relationships between MCGN, C3NeF and partial lipodystrophy, also characterised by C3NeF and hypocomplementaemia, but preceding the development of MCGN, suggest that hypocomplementaemia predisposes to MCGN. Another possibility is that C3NeF acts directly within glomeruli to cause local complement activation and ensuing damage. Neither possibility could be resolved, but some recent observations have restimulated interest in a possible causative role for C3NeF in MCGN. First, factor H deficiency, by mechanisms other than blocking by C3NeF, in animals and man is associated with MCGN. Second, adipocytes, now known themselves to produce complement system proteins, are lysed in vitro by C3NeF, thus suggesting a mechanism for partial lipodystrophy. By analogy, the C3NeF may produce glomerular damage, as glomerular cells produce complement components. Received July 18, 1996; accepted July 24, 1996     

Soluble CR1 Therapy Improves Complement Regulation in C3 Glomerulopathy

Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are widely recognized subtypes of C3 glomerulopathy. These ultra-rare renal diseases are characterized by fluid-phase dysregulation of the alternative complement pathway that leads to deposition of complement proteins in the renal glomerulus. Disease triggers are unknown and because targeted treatments are lacking, progress to end stage renal failure is a common final outcome. We studied soluble CR1, a potent regulator of complement activity, to test whether it restores complement regulation in C3 glomerulopathy. In vitro studies using sera from patients with DDD showed that soluble CR1 prevents dysregulation of the alternative pathway C3 convertase, even in the presence of C3 nephritic factors. In mice deficient in complement factor H and transgenic for human CR1, soluble CR1 therapy stopped alternative pathway activation, resulting in normalization of serum C3 levels and clearance of iC3b from glomerular basement membranes. Short-term use of soluble CR1 in a pediatric patient with end stage renal failure demonstrated its safety and ability to normalize activity of the terminal complement pathway. Overall, these data indicate that soluble CR1 re-establishes regulation of the alternative complement pathway and provide support for a limited trial to evaluate soluble CR1 as a treatment for DDD and C3GN.Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are two widely recognized subtypes of C3 glomerulopathy (C3G).^1,2 These ultra-rare renal diseases are caused by fluid-phase dysregulation of the C3 convertase of the alternative pathway (AP) of complement, with variable concomitant dysregulation of the C5 convertase. Consistent with complement-mediated disease acting through the AP, C3G is strongly positive for C3 and notably negative for Igs by immunofluorescence microscopy.² Electron microscopy distinguishes DDD from C3GN, with the former characterized by pathognomonic electron-dense transformation of the lamina densa of the glomerular basement membrane (GBM).³ In C3GN, the electron microscopy deposits are lighter in color, and are more often mesangial and/or subendothelial, intramembranous, and subepithelial in location.⁴ In both diseases, mass spectroscopy of laser dissected glomeruli is highly enriched for proteins of the AP and terminal complement cascade.^4,5 Although long-term outcome data are not available for C3GN, nearly half of all DDD patients progress to end stage renal failure (ESRF) within 10 years of diagnosis.^6,7 In virtually all cases of DDD, transplantation is associated with histologic recurrence, explaining the 5-year graft failure rate of 50%.^7,8 There are no target-specific treatments for C3G; however, its pathophysiology suggests that therapeutic approaches to restore C3 convertase control, impair C3 convertase activity, or remove C3 breakdown products from the circulation warrant consideration.^1,9Similar to human DDD, the complement factor H (Cfh)–deficient mouse, reclassified recently as a murine model of C3GN, accumulates C3 fragments within glomeruli as the first pathologic abnormality to develop.¹⁰ Systemic administration of either murine or human complement factor H (fH) to the Cfh−/− mouse rapidly reverses both the renal deposition of C3 and its plasma depletion, suggesting that fH replacement therapy may be an effective therapy to restore the underlying protein deficiency and correct the disease process in C3G patients with CFH mutations.^11,12 However, it is unlikely that fH administration would be therapeutically successful in the absence of CFH-inactivating mutations. For example, fH would be ineffective in C3G patients carrying C3 mutations that render C3 convertase fH resistant or in the presence of autoantibodies to C3 convertase that block regulation by fH.^13,14Among the non-fH proteins that regulate C3 convertase is soluble CR1. CR1 is a cell-surface glycoprotein expressed on erythrocytes, monocytes, neutrophils, B cells, some T cells, follicular dendritic cells, and podocytes, and modulates the complement cascade at multiple levels (Supplemental Figures 1 and 2).^15–18 It is composed of 30 short consensus repeats (SCRs) linked to transmembrane and cytosolic domains.¹⁹ On the basis of SCR sequence homology, the 30 extracellular SCRs can be grouped into four long homologous repeats, which are sequentially lettered A through D. These long homologous repeats give CR1 C3 and C5 convertase-controlling activity. CR1 is also the only cofactor of factor I (fI) to promote cleavage of inactive C3b and inactive C4b into their smaller protein fragments, C3dg and C4d.^20–22The soluble form of CR1 (sCR1) is present in the circulation at extremely low concentrations precluding any recognized physiologic significance. However, super-physiologic single-dose treatment with sCR1 has been used in >500 patients (infants and adults) undergoing a variety of cardiac surgeries or after myocardial infarctions to arrest complement activation.^23–26 These studies showed that sCR1 was well tolerated with no adverse events clearly or consistently associated with its use. Importantly, the possible development of anti-sCR1 antibodies was monitored but never observed in >350 patients.^23,26     

Crescentic and necrotizing glomerulonephritis with C3 deposition

Case 1: A 38-year-old female with a history of tonsillitis and sinusitis was admitted to our hospital because of lung edema. On admission, her serum creatinine increased to 5.57 mg/dL. Hypocomplementemia was not found. ASO and MPO-ANCA were 24 U/mL and 12 EU, respectively. She underwent emergency hemodialysis. Renal biopsy showed global sclerosis and fibrocellular crescentic formation, and marked angionecrosis was noted by light microscopy. Granular deposition of C3, IgG and IgM was seen along the capillary walls on immunofluorescence study. Glomerular intramembranous deposits were scattered on electron microscopy. She was treated with intravenous methylprednisolone pulse therapy, and following oral prednisolone administration was decreased gradually. No therapeutic effects were observed, and intermittent hemodialysis was continued and became maintenance hemodialysis therapy. Case 2: A 28-year-old female suffering from both pharyngitis and acute renal failure with systemic edema was admitted to our hospital. On admission, her serum creatinine and ASO were 4.31 mg/dL and 239 U/mL, respectively. MPO-ANCA was negative and CH50 was normal. Hemodialysis was initiated on the 6th hospital day. In renal biopsy, most glomeruli showed cellular crescentic formation, and marked angionecrosis was noted by light microscopy. Global sclerosis was not found in this case. Granular deposition of C3 resembling a starry sky pattern was seen along the capillary walls on immunofluorescence study. Electron microscopy revealed scattered glomerular subepithelial deposits. She was treated with intravenous methylprednisolone pulse therapy and then oral prednisolone administration. Because of the gradual improvement in renal function, hemodialysis was terminated after 53 sessions, however, the patient's chronic renal failure has persisted to date. In these two cases, the pathological findings supported the diagnosis of severe acute post-infectious glomerulonephritis with the characteristic crescentic and necrotizing glomerulonephritis with C3 deposition.     

Loss of Properdin Exacerbates C3 Glomerulopathy Resulting from Factor H Deficiency

Complement factor H (CFH) is a negative regulator of the alternative pathway of complement, and properdin is the sole positive regulator. CFH-deficient mice (CFH^−/−) develop uncontrolled C3 activation and spontaneous renal disease characterized by accumulation of C3 along the glomerular basement membrane, but the role of properdin in the pathophysiology is unknown. Here, we studied mice deficient in both CFH and properdin (CFH^−/−.P^−/−). Although CFH^−/− mice had plasma depleted of both C3 and C5, CFH^−/−.P^−/− animals exhibited depletion of C3 predominantly, recapitulating the plasma complement profile observed in humans with properdin-independent C3 nephritic factors. Glomerular inflammation, thickening of the capillary wall, and glomerular C3 staining were significantly increased in CFH^−/−.P^−/− compared with CFH^−/− mice. We previously reported that exogenous CFH ameliorates C3 staining of the glomerular basement membrane and triggers the appearance of mesangial C3 deposits in CFH^−/− mice; here, we show that these effects require properdin. In summary, during uncontrolled activation of C3 driven by complete CFH deficiency, properdin influences the intraglomerular localization of C3, suggesting that therapeutic inhibition of properdin would be detrimental in this setting.The complement system is an integral component of the host response to pathogens. Regulation of complement is achieved by a group of proteins located in plasma and on cell membranes that act collectively to prevent inappropriate complement activation on host tissues. Abnormalities in complement regulation are associated with renal disease.^1,2 Specifically, there is a strong association between abnormal regulation of the complement alternative pathway (AP) and C3 glomerulopathy. C3 glomerulopathy refers to glomerular pathologies characterized by isolated glomerular accumulation of complement C3.¹ Examples include dense deposit disease (DDD), C3 GN, and CFHR5 nephropathy. In these conditions, genetic and acquired factors that result in uncontrolled AP regulation may be seen.^1,2 These factors include loss of function mutations in the AP regulatory protein complement factor H (CFH) and gain of function mutations in the AP activation protein, C3. Acquired factors include autoantibodies that stabilize the AP C3 convertase.The mechanism through which uncontrolled C3 activation results in accumulation of C3 within the glomerulus has been partially elucidated through the study of murine models of AP dysregulation.³ Gene-targeted CFH-deficient mice (CFH^−/−) develop uncontrolled AP activation, which results in secondary depletion of plasma C3.⁴ These animals develop marked accumulation of C3 along the glomerular basement membrane (GBM) and subsequently both morphologic changes to the GBM (subendothelial electron-dense C3-containing deposits) and glomerular inflammation (typically membranoproliferative GN [MPGN]). Similar pathology has also been described in a breed of pigs with spontaneous CFH deficiency.⁵ Importantly, renal C3 accumulation in the murine model was absolutely dependent on the ability to activate the AP: mice with deficiency of both CFH and the AP activation protein, factor B, did not develop renal injury or plasma C3 depletion. C3 accumulation along the GBM in the setting of CFH deficiency is also dependent on complement factor I (CFI). CFI is an enzyme that cleaves activated C3 (termed C3b) to iC3b. Experiments in mice with combined deficiency of CFH and CFI suggested that it is iC3b that targets the GBM during uncontrolled AP activation due to CFH deficiency.⁶Properdin is the only positive regulator of complement activation.⁷ It stabilizes the AP C3 convertase, which in its absence rapidly and spontaneously decays. Properdin deficiency in humans is associated with increased susceptibility to Neisserial infections.^8–10 Based on our current understanding of the pathogenesis of C3 glomerulopathy,^1,2 enhancing properdin activity (e.g., through gain of function mutations) would, through increased AP activation, be predicted to exacerbate C3 glomerulopathy. Conversely, reducing properdin activity (e.g., through genetic or therapeutic manipulation) would, through reduced AP activation, be predicted to ameliorate C3 glomerulopathy. To date these scenarios have not been described in human pathology. Here, through the study of gene-targeted properdin-deficient mice, we investigate the contribution of properdin to both spontaneous and experimentally triggered renal disease in CFH^−/− mice. Unexpectedly, our data demonstrated that coexisting properdin deficiency did not confer a beneficial effect on renal disease in CFH^−/− animals. In fact, glomerular inflammation and accumulation of glomerular C3 were enhanced in mice with combined deficiency of CFH and properdin (CFH^−/−.P^−/−).