A novel inhibitor of the alternative complement pathway prevents antiphospholipid antibody-induced pregnancy loss in mice

Thurman, Joshua M.; Kraus, Damian; Girardi, Guillermina; Hourcade, Dennis E.; Kang, Hee Jung; Royer, P; Mitchell, Lynne M.; Giclas, Patricia C.; Salmon, Jane E.; Gilkeson, Gary S.; Holers, V. Michael

doi:10.1016/j.molimm.2004.07.043

Cited by 154 publications

(140 citation statements)

References 26 publications

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“…To do this we tested the ability of purified microparticles to restore alternative pathway activity to factor D depleted serum. Zymosan particles activate the alternative pathway when incubated with serum 42. As expected, no alternative pathway activity was seen when factor D–depleted serum was used in this assay (Figure 5A).…”

Section: Resultssupporting

confidence: 69%

“…To measure alternative pathway activity, zymosan A particles (Sigma‐Aldrich, St. Louis, MO) were incubated with human serum, and C3 deposition on the particles was measured as previously described 42. Briefly, 10 μL of serum was incubated with 10 9 zymosan particles at 37°C for 30 minutes in a master mix containing 5 mmol/L MgCl 2 and 10 mmol/L EGTA.…”

Section: Methodsmentioning

confidence: 99%

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Endothelial Microparticles and Systemic Complement Activation in Patients With Chronic Kidney Disease

Jalal

Renner

Laskowski

et al. 2018

JAHA

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BackgroundEndothelial microparticles are associated with chronic kidney disease (CKD) and complement activation. We hypothesized that the complement pathway is activated in patients with CKD via endothelial microparticles and that complement activation correlates with endothelial dysfunction in CKD.Methods and ResultsWe analyzed complement data of 30 healthy subjects, 30 patients with stage III/IV CKD, and 30 renal transplant recipients with stage III/IV CKD, evaluating the potential correlation of complement fragments with brachial artery flow–mediated dilation, Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate, and urinary albumin/creatinine ratio. Endothelial microparticles were characterized via proteomic analysis and compared between study groups. Complement fragment Ba was significantly increased in CKD and post–kidney transplant CKD. Plasma Ba levels correlated significantly with lower brachial artery flow–mediated dilation, lower Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate, and higher urinary albumin/creatinine ratio. Factor D levels were significantly higher in the plasma microparticles of patients with CKD versus healthy controls. Plasma microparticles isolated from patients with CKD and containing factor D activated the alternative pathway in vitro.ConclusionThe alternative complement pathway is activated in CKD and correlates with endothelial dysfunction and markers of CKD. Future studies are needed to evaluate whether endothelial microparticles with increased factor D play a pathologic role in CKD‐associated vascular disease.Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT02230202.

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Section: Resultssupporting

confidence: 69%

Section: Methodsmentioning

confidence: 99%

Endothelial Microparticles and Systemic Complement Activation in Patients With Chronic Kidney Disease

Jalal

Renner

Laskowski

et al. 2018

JAHA

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“…3b). Changes in the CCP2-CCP3 interface reduce C3b binding and hemolytic activity 22,23 , and antibodies directed against CCP1 and CCP3 block hemolytic activity 22,24 ( Supplementary Fig. 4 online), indicating that the triad of CCP domains provides an important binding site for C3b.…”

Section: Triad Of Ccp Domainsmentioning

confidence: 99%

Factor B structure provides insights into activation of the central protease of the complement system

Milder

Gomes

Schouten

et al. 2007

Nat Struct Mol Biol

105

141

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Factor B is the central protease of the complement system of immune defense. Here, we present the crystal structure of human factor B at 2.3-Å resolution, which reveals how the five-domain proenzyme is kept securely inactive. The canonical activation helix of the Von Willebrand factor A (VWA) domain is displaced by a helix from the preceding domain linker. The two helices conformationally link the scissile-activation peptide and the metal ion-dependent adhesion site required for binding of the ligand C3b. The data suggest that C3b binding displaces the three N-terminal control domains and reshuffles the two central helices.Reshuffling of the helices releases the scissile bond for final proteolytic activation and generates a new interface between the VWA domain and the serine protease domain. This allosteric mechanism is crucial for tight regulation of the complementamplification step in the immune response.Factor B is a tightly regulated, highly specific serine protease. In its activated form, it catalyzes the central amplification step of complement activation to initiate inflammatory responses, cell lysis, phagocytosis and B-cell stimulation 1,2 . Factor B is activated through an assembly process: it binds surface-bound C3b, or its fluid-phase counterpart C3(H 2 O), after which it is cleaved by factor D into fragments Ba (residues 1-234) and Bb (residues 235-739) 3,4 . Fragment Ba dissociates from the complex, leaving behind the alternative pathway C3 convertase complex C3b-Bb, which cleaves C3 into C3a and C3b (see Fig. 1a). This protease complex is intrinsically instable. Once dissociated from the complex, Bb cannot reassociate with C3b 5 . A similar C3 convertase complex is formed upon activation of the classical (antibody-mediated) and lectin-binding pathways, comprised of C4 and C2, which are homologous to C3 and factor B, respectively. The proenzyme factor B consists of three N-terminal complement control protein (CCP) domains, connected by a 45-residue linker to a VWA domain and a C-terminal serine protease (SP) domain, which carries the catalytic center (Fig. 1a). The VWA and SP domains form fragment Bb, and CCP1 through CCP3 and the linker form fragment Ba. Binding of factor B to C3b depends on elements in fragment Ba 6 and the Mg 2+ -dependent metal ion-dependent adhesion site (MIDAS) motif in the VWA domain of fragment Bb 7 . The VWA domain is structurally homologous to inserted (I) domains in integrins. In I domains, ligand binding to the MIDAS is coupled to a B10-Å shift of the a7 activation helix, with concomitant domain rearrangements that activate the integrins 8,9 . Structures of a truncated Bb fragment 10 and its full-length homolog C2a 11 show variable positions of the a7 activation helix affecting the orientation of the VWA and SP domains, which indicates that a related mechanism may occur in convertase formation and dissociation. These structures, however, do not reveal the regulation of the proteolytic activity of factor B. In particular, it is unclear how factor B is maintained in its in...

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“…Alternative pathway integrity was measured using a modification of the zymosan assay (Thurman et al 2005;Foley et al 1993). Activated zymosan particles (CompTech, Tyler, TX, 1×10 6 per reaction) were added to 100 µl veronal buffered saline containing either 2 mM MgCl 2 plus 10 mM EGTA (experimental sample), or 10 mM EDTA (negative control).…”

Section: Alternative Pathway Zymosan Assaymentioning

confidence: 99%

“…However, these analyses do not distinguish between the possibilities that any of these traditional upstream pathways may be sufficient to activate C3 and promote normal liver regeneration or, alternatively, that non-traditional mechanisms activate complement signaling during liver regeneration. To investigate these considerations, the hepatic regenerative response was evaluated in C4-null mice treated with a well characterized anti-factor B neutralizing monoclonal antibody (mAb 1379, (Leinhase et al 2007; Taube et al 2006;Thurman et al 2005). In these animals, the classical and lectin-dependent pathways are blocked by genetic disruption of C4 expression (Figure 1) while the alternative pathway is entirely suppressed by the neutralizing antibody ( Figure 4B).…”

Section: Liver Regeneration and C3 Activation Occur Normally In C4-numentioning

confidence: 99%

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration

Clark

Weymann

Hartman

et al. 2008

Molecular Immunology

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Complement signaling has been implicated as important for normal hepatic regeneration. However, the specific mechanism by which complement is activated during liver regeneration remains undefined. To address this question, we investigated the hepatic regenerative response to partial hepatectomy in wildtype mice, C3-, C4-, and factor B-null mice, and C4-null mice treated with a factor B neutralizing antibody (mAb 1379). The results showed that following partial hepatectomy, C3-null mice exhibit reduced hepatic regeneration compared to wildtype mice as assessed by quantification of hepatic cyclin D1 expression and hepatocellular DNA synthesis and mitosis. In contrast, C4-null mice and factor B-null mice demonstrated normal liver regeneration. Moreover, animals in which all of the traditional upstream C3 activation pathways were disrupted, i.e. C4-null mice treated with mAb 1379, exhibited normal C3 activation and hepatocellular proliferation following partial hepatectomy. In order to define candidate non-traditional mechanisms of C3 activation during liver regeneration, plasmin and thrombin were investigated for their abilities to activate C3 in mouse plasma in vitro. The results showed that both proteases are capable of initiating C3 activation, and that plasmin can do so independent of the classical and alternative pathways.Conclusions-These results show that C3 is required for a normal hepatic regenerative response, but that disruption of the classical-or lectin-dependent pathways (C4-dependent), the alternative pathway (factor B-dependent), or all of these pathways does not impair the hepatic regenerative response, and indicate that non-traditional mechanisms by which C3 is activated during hepatic regeneration must exist. In vitro analysis raises the possibility that plasmin may contribute to nontraditional complement activation during liver regeneration in vivo.

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A novel inhibitor of the alternative complement pathway prevents antiphospholipid antibody-induced pregnancy loss in mice

Cited by 154 publications

References 26 publications

Endothelial Microparticles and Systemic Complement Activation in Patients With Chronic Kidney Disease

Endothelial Microparticles and Systemic Complement Activation in Patients With Chronic Kidney Disease

Factor B structure provides insights into activation of the central protease of the complement system

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration

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