Interaction of C3b2–IgG complexes with complement proteins properdin, factor B and factor H: implications for amplification

2000 ◽  
Vol 349 (1) ◽  
pp. 217-223
Author(s):  
Emiliana JELEZAROVA ◽  
Anna VOGT ◽  
Hans U. LUTZ
Keyword(s):  
Present Report ◽  
Alternative Pathway ◽  
Fluid Phase ◽  
Factor H ◽  
Complement Protein ◽  
Factor B ◽  
Physiological Conditions ◽  
Amplification Loop ◽  
Target Molecules ◽  
Properdin Factor B

Nascent C3b can form ester bonds with various target molecules on the cell surface and in the fluid phase. Previously, we showed that C3b2-IgG complexes represent the major covalent product of C3 activation in serum [Lutz, Stammler, Jelezarova, Nater and Späth (1996) Blood 88, 184-193]. In the present report, binding of alternative pathway proteins to purified C3b2-IgG complexes was studied in the fluid phase by using biotinylated IgG for C3b2-IgG generation and avidin-coated plates to capture complexes. Up to seven moles of properdin ‘monomer’ bound per mole of C3b2-IgG at physiological conditions in the absence of any other complement protein. At low properdin/C3b2-IgG ratios bivalent binding was preferred. Neither factor H nor factor B affected properdin binding. On the other hand, properdin strongly stimulated factor B binding. Interactions of all three proteins with C3b2-IgG exhibited pH optima. An ionic strength optimum was most pronounced for properdin, while factor B binding was largely independent of the salt concentration. C3b2-IgG complexes were powerful precursors of the alternative pathway C3 convertase. In the presence of properdin, C3 convertase generated from C3b2-IgG cleaved about sevenfold more C3 than the enzyme generated on C3b. C3b2-IgG complexes could therefore maintain the amplification loop of complement longer than free C3b.

scholarly journals Modulation of complement activation on hemodialysis membranes by immobilized heparin.

1992 ◽  
Vol 2 (8) ◽  
pp. 1328-1337
Author(s):  
A K Cheung ◽  
C J Parker ◽  
J Janatova ◽  
E Brynda
Keyword(s):  
Complement Activation ◽  
Alternative Pathway ◽  
Membrane Surface ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Fluid Phase ◽  
Factor H ◽  
Binding Studies ◽  
Factor B ◽  
Pathway Activity

To determine the effects of surface-associated heparin on the capacity of hemodialysis membranes to activate complement, cellulose acetate (CA) membranes that were untreated and CA membranes that had been coated with heparin (HCA) were incubated with C3-depleted serum repleted with radio-labeled C3. Next, the proteins in the supernatant and those eluted from the membranes were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. C3 activation was quantified by determining the radioactivity of the C3a-containing band in the gel. Total C3a generation (fluid phase C3a plus membrane-associated C3a) was three times greater in the presence of HCA compared with CA. Most (88%) of the C3a generated in the presence of HCA, however, was adsorbed onto the membrane surface. Consequently, there was more C3a in the CA supernatant than in the HCA supernatant. To determine the mechanism by which heparin enhanced alternative pathway activity, binding studies with radiolabeled factor B and factor H were performed. HCA bound 3.4 times more factor B and 20 times more factor H than did CA. The binding of these proteins, however, was not dependent on complement activation. Studies designed to test the functional activity of isolated factor H and factor B that had been adsorbed to the membrane showed that factor H was active on both CA and HCA, whereas factor B was active only on HCA. These data demonstrate that heparin immobilized onto CA hemodialysis membrane enhances C3 activation but produces low levels of C3a in the fluid phase because of high surface adsorption of the anaphylatoxin. Heparin appears to augment alternative pathway activity by favoring the interactions of factor B with other constituents of the amplification C3 convertase of the alternative pathway of complement.

scholarly journals The alternative complement pathway is activated in protoporphyria patients during sun exposure

2020 ◽  
Author(s):  
Francesca Granata ◽  
Lorena Duca ◽  
Valentina Brancaleoni ◽  
Silvia Fustinoni ◽  
Giacomo De Luca ◽  
...  
Keyword(s):  
Light Exposure ◽  
Alternative Pathway ◽  
Global Radiation ◽  
Protoporphyrin Ix ◽  
Sun Exposure ◽  
Factor H ◽  
Factor B ◽  
Alternative Complement ◽  
Differential Involvement ◽  
The Complement System

ABSTRACTThe homeostasis of tissues in chronic disease is an important function of the alternative pathway (AP) of the complement system (CS). However, if not controlled, it may also be detrimental to healthy cells.Protoporphyria (PP) is a rare disease that causes photosensitivity at the visible light due to the accumulation of Protoporphyrin-IX in the dermis. The aim of this study was to deep the knowledge about the involvement of AP in PP photoreaction.Global radiation and UV data were provided from regional agency of environmental protection (ARPA). Properdin, Factor H (FH) and C5 levels were assessed in the serum collected during winter and summer from 19 PP patients and 13 controls..Properdin in winter and summer reflected a positive increase compared to controls. The values in summer were higher than winter. The C5 results were altered only in summer. The outcome was reversed for FH: in the winter, it was higher compared to the summer. A positive correlation was reported between properdin and C3 in summer; a negative tendency between Factor B (FB) and FH was detected.This study substantiated the differential involvement of AP depending on the increase in light exposure during the season, which was demonstrated with ARPA data. The enhanced systemic response could justify the malaise sensation of patients after long light exposure and can be exploited to elucidate the new therapeutic approach.

scholarly journals Complement Activation via Alternative Pathway Is Critical in the Development of Laser-Induced Choroidal Neovascularization: Role of Factor B and Factor H

2006 ◽  
Vol 177 (3) ◽  
pp. 1872-1878 ◽  
Author(s):  
Nalini S. Bora ◽  
Sankaranarayanan Kaliappan ◽  
Purushottam Jha ◽  
Qin Xu ◽  
Jeong-Hyeon Sohn ◽  
...  
Keyword(s):  
Choroidal Neovascularization ◽  
Complement Activation ◽  
Alternative Pathway ◽  
Factor H ◽  
Factor B

scholarly journals The Human Complement Regulator Factor H Binds Pneumococcal Surface Protein PspC via Short Consensus Repeats 13 to 15

2002 ◽  
Vol 70 (10) ◽  
pp. 5604-5611 ◽  
Author(s):  
Thomas G. Duthy ◽  
Rebecca J. Ormsby ◽  
Eleni Giannakis ◽  
A. David Ogunniyi ◽  
Uwe H. Stroeher ◽  
...  
Keyword(s):  
Alternative Pathway ◽  
Regulatory System ◽  
Surface Protein ◽  
Fluid Phase ◽  
Direct Consequence ◽  
Factor H ◽  
Negative Regulator ◽  
Short Consensus Repeats ◽  
High Concentrations ◽  
Complement Regulator

ABSTRACT The innate ability of Streptococcus pneumoniae to resist complement activation and complement-mediated phagocytosis may be a direct consequence of the ability of the bacteria to bind components of the complement regulatory system. One such component, factor H (fH), is a crucial fluid-phase negative regulator of the alternative pathway of complement and is utilized by a number of pathogenic organisms to resist complement attack. The pneumococcal surface protein C (PspC [also known as CbpA] and SpsA) has been shown to bind fH, although the exact binding site within one or more of the 20 short consensus repeats (SCRs) of the molecule is not known. The purpose of the current study was to map specific SCRs on fH responsible for this binding. Initial experiments utilizing type 2 pneumococcal strain D39 and its isogenic PspC-negative derivative (D39/pspC mutant) showed that fH binding was PspC dependent. A purified recombinant protein derivative of PspC that lacked the proline-rich region (PspCΔPro) had a reduced binding efficiency for fH, thereby directly showing the importance of this region for the fH interaction. We have specifically shown by inhibition experiments that SCRs responsible for heparin and C3b binding of fH are not involved in binding PspC and the interaction between fH and PspC is largely hydrophobic, since no inhibition was observed in the presence of high concentrations of NaCl. Construction of SCR proteins encompassing the whole fH molecule showed that SCRs 8 to 15 (SCR 8-15) mediated binding to PspC. Further localization experiments revealed that SCR 13 and SCR 15 were required for full binding, although partial binding was retained when either SCR was removed.

scholarly journals Hijacking Factor H for Complement Immune Evasion

2021 ◽  
Vol 12 ◽  
Author(s):  
Sara R. Moore ◽  
Smrithi S. Menon ◽  
Claudio Cortes ◽  
Viviana P. Ferreira
Keyword(s):  
Host Cell ◽  
Complement System ◽  
Alternative Pathway ◽  
Expression Patterns ◽  
Fluid Phase ◽  
Factor H ◽  
Host Cells ◽  
Complement C3 ◽  
Complement Regulators ◽  
The Complement System

The complement system is an essential player in innate and adaptive immunity. It consists of three pathways (alternative, classical, and lectin) that initiate either spontaneously (alternative) or in response to danger (all pathways). Complement leads to numerous outcomes detrimental to invaders, including direct killing by formation of the pore-forming membrane attack complex, recruitment of immune cells to sites of invasion, facilitation of phagocytosis, and enhancement of cellular immune responses. Pathogens must overcome the complement system to survive in the host. A common strategy used by pathogens to evade complement is hijacking host complement regulators. Complement regulators prevent attack of host cells and include a collection of membrane-bound and fluid phase proteins. Factor H (FH), a fluid phase complement regulatory protein, controls the alternative pathway (AP) both in the fluid phase of the human body and on cell surfaces. In order to prevent complement activation and amplification on host cells and tissues, FH recognizes host cell-specific polyanionic markers in combination with complement C3 fragments. FH suppresses AP complement-mediated attack by accelerating decay of convertases and by helping to inactivate C3 fragments on host cells. Pathogens, most of which do not have polyanionic markers, are not recognized by FH. Numerous pathogens, including certain bacteria, viruses, protozoa, helminths, and fungi, can recruit FH to protect themselves against host-mediated complement attack, using either specific receptors and/or molecular mimicry to appear more like a host cell. This review will explore pathogen complement evasion mechanisms involving FH recruitment with an emphasis on: (a) characterizing the structural properties and expression patterns of pathogen FH binding proteins, as well as other strategies used by pathogens to capture FH; (b) classifying domains of FH important in pathogen interaction; and (c) discussing existing and potential treatment strategies that target FH interactions with pathogens. Overall, many pathogens use FH to avoid complement attack and appreciating the commonalities across these diverse microorganisms deepens the understanding of complement in microbiology.

scholarly journals Limited tryptic cleavage of complement factor H abrogates recognition of sialic acid-containing surfaces by the alternative pathway of complement

1992 ◽  
Vol 283 (2) ◽  
pp. 317-319 ◽  
Author(s):  
V Koistinen
Keyword(s):  
Sialic Acid ◽  
Cleavage Site ◽  
Alternative Pathway ◽  
Factor H ◽  
Complement Factor H ◽  
Complement Factor ◽  
Complement Protein ◽  
Sheep Erythrocytes ◽  
Tryptic Cleavage ◽  
N Terminus

The potency of complement factor H (H) in accelerating the decay of the alternative pathway C3 convertase, C3b,Bb (decay-accelerating activity), was used as a measure of the affinity of native versus trypsin-treated H for the complement protein C3b bound to surfaces. When about 99% of H was cleaved at the primary tryptic cleavage site 34 kDa from the N-terminus, its decay-accelerating activity on C3b,Bb on sheep erythrocytes fell about 60-fold, whereas the trypsin-treated H was only 3-4 times less potent than native H in dissociating C3b,Bb on Sepharose 4B. The residual decay-accelerating activity, remaining after the primary cleavage, was not affected by secondary cleavage at a site 120 kDa from the N-terminus, as shown with H preparations cleaved to different degrees. Because cell surface sialic acid is known to be responsible for the high affinity of H for C3b bound on sheep erythrocytes, the results strongly suggest that the integrity of the primary tryptic cleavage site of H is essential for the recognition of sialic acid-containing surfaces by the C3b-H complex.

scholarly journals Factor H Autoantibodies and Complement-Mediated Diseases

2020 ◽  
Vol 11 ◽  
Author(s):  
Yuzhou Zhang ◽  
Nicolo Ghiringhelli Borsa ◽  
Dingwu Shao ◽  
Arthur Dopler ◽  
Michael B. Jones ◽  
...  
Keyword(s):  
Tissue Injury ◽  
Alternative Pathway ◽  
Phenotypic Variability ◽  
Atypical Hemolytic Uremic Syndrome ◽  
Fluid Phase ◽  
Factor H ◽  
Regulatory Function ◽  
Regulators Of Complement Activation ◽  
Uremic Syndrome ◽  
Genetic Deletion

Factor H (FH), a member of the regulators-of-complement-activation (RCA) family of proteins, circulates in human plasma at concentrations of 180–420 mg/L where it controls the alternative pathway (AP) of complement in the fluid phase and on cell surfaces. When the regulatory function of FH is impaired, complement-mediated tissue injury and inflammation occur, leading to diseases such as atypical hemolytic uremic syndrome (a thrombotic microangiopathy or TMA), C3 glomerulopathy (C3G) and monoclonal gammopathy of renal significance (MGRS). A pathophysiological cause of compromised FH function is the development of autoantibodies to various domains of the FH protein. FH autoantibodies (FHAAs) are identified in 10.9% of patients with aHUS, 3.2% of patients with C3G, and rarely in patients with MGRS. The phenotypic variability of FHAA-mediated disease reflects both the complexity of FH and the epitope specificity of FHAA for select regions of the native protein. In this paper, we have characterized FHAA epitopes in a large cohort of patients diagnosed with TMA, C3G or MGRS. We explore the epitopes recognized by FHAAs in these diseases and the association of FHAAs with the genetic deletion of both copies of the CFHR1 gene to show how these disease phenotypes are associated with this diverse spectrum of autoantibodies.

scholarly journals Borrelia burgdorferi Binding of Host Complement Regulator Factor H Is Not Required for Efficient Mammalian Infection

2007 ◽  
Vol 75 (6) ◽  
pp. 3131-3139 ◽  
Author(s):  
Michael E. Woodman ◽  
Anne E. Cooley ◽  
Jennifer C. Miller ◽  
John J. Lazarus ◽  
Kathryn Tucker ◽  
...  
Keyword(s):  
Lyme Disease ◽  
Borrelia Burgdorferi ◽  
Alternative Pathway ◽  
Host Factor ◽  
Factor H ◽  
Surface Proteins ◽  
Wild Type ◽  
Factor B ◽  
Mammalian Infection ◽  
Deficient Mice

ABSTRACT The causative agent of Lyme disease, Borrelia burgdorferi, is naturally resistant to its host's alternative pathway of complement-mediated killing. Several different borrelial outer surface proteins have been identified as being able to bind host factor H, a regulator of the alternative pathway, leading to a hypothesis that such binding is important for borrelial resistance to complement. To test this hypothesis, the development of B. burgdorferi infection was compared between factor H-deficient and wild-type mice. Factor B- and C3-deficient mice were also studied to determine the relative roles of the alternative and classical/lectin pathways in B. burgdorferi survival during mammalian infection. While it was predicted that B. burgdorferi should be impaired in its ability to infect factor H-deficient animals, quantitative analyses of bacterial loads indicated that those mice were infected at levels similar to those of wild-type and factor B- and C3-deficient mice. Ticks fed on infected factor H-deficient or wild-type mice all acquired similar numbers of bacteria. Indirect immunofluorescence analysis of B. burgdorferi acquired by feeding ticks from the blood of infected mice indicated that none of the bacteria had detectable levels of factor H on their outer surfaces, even though such bacteria express high levels of surface proteins capable of binding factor H. These findings demonstrate that the acquisition of host factor H is not essential for mammalian infection by B. burgdorferi and indicate that additional mechanisms are employed by the Lyme disease spirochete to evade complement-mediated killing.

scholarly journals Hyperfunctional C3 convertase leads to complement deposition on endothelial cells and contributes to atypical hemolytic uremic syndrome

Blood ◽  
2009 ◽  
Vol 114 (13) ◽  
pp. 2837-2845 ◽  
Author(s):  
Lubka T. Roumenina ◽  
Mathieu Jablonski ◽  
Christophe Hue ◽  
Jacques Blouin ◽  
Jordan D. Dimitrov ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Hemolytic Uremic Syndrome ◽  
Umbilical Vein ◽  
Alternative Pathway ◽  
Atypical Hemolytic Uremic Syndrome ◽  
Factor H ◽  
Immune Defense ◽  
Factor B ◽  
Uremic Syndrome ◽  
Complement Deposition

Abstract Complement is a major innate immune defense against pathogens, tightly regulated to prevent host tissue damage. Atypical hemolytic uremic syndrome (aHUS) is characterized by endothelial damage leading to renal failure and is highly associated with abnormal alternative pathway regulation. We characterized the functional consequences of 2 aHUS-associated mutations (D254G and K325N) in factor B, a key participant in the alternative C3 convertase. Mutant proteins formed high-affinity C3-binding site, leading to a hyperfunctional C3 convertase, resistant to decay by factor H. This led to enhanced complement deposition on the surface of alternative pathway activator cells. In contrast to native factor B, the 2 mutants bound to inactivated C3 and induced formation of functional C3-convertase on iC3b-coated surface. We demonstrated for the first time that factor B mutations lead to enhanced C3-fragment deposition on quiescent and adherent human glomerular cells (GEnCs) and human umbilical vein endothelial cells (HUVECs), together with the formation of sC5b-9 complexes. These results could explain the occurrence of the disease, since excessive complement deposition on endothelial cells is a central event in the pathogenesis of aHUS. Therefore, risk factors for aHUS are not only mutations leading to loss of regulation, but also mutations, resulting in hyperactive C3 convertase.

scholarly journals Changes in complement alternative pathway components, factor B and factor H during dengue virus infection in the AG129 mouse

2021 ◽  
Author(s):  
Sheila Cabezas-Falcon ◽  
Aidan J. Norbury ◽  
Jarrod Hulme-Jones ◽  
Sonja Klebe ◽  
Penelope Adamson ◽  
...  
Keyword(s):  
Dengue Virus ◽  
Alternative Pathway ◽  
Severe Disease ◽  
Denv Infection ◽  
Factor H ◽  
Severe Dengue ◽  
Complement Alternative Pathway ◽  
Factor B ◽  
Dengue Disease

The complement alternative pathway (AP) is tightly regulated and changes in two important AP components, factor B (FB) and factor H (FH) are linked to severe dengue in humans. Here, a mouse model of dengue was investigated to define the changes in FB and FH and assess the utility of this model to study the role of the AP in severe dengue. Throughout the period of viremia in the AG129 IFN signalling-deficient mouse, an increase in FB and a decrease in FH was observed following dengue virus (DENV) infection, with the former only seen in a model of more severe disease associated with antibody-dependent enhancement (ADE). Terminal disease was associated with a decrease in FB and FH, with greater changes during ADE, and accompanied by increased C3 degradation consistent with complement activation. In silico analysis of NFκΒ, signal transducer and activator of transcription (STAT) and IFN-driven FB and FH promoter elements to reflect the likely impact of the lack of IFN-responses in AG129 mice, demonstrated that these elements differed markedly between human and mouse, notably with mouse FH lacking NFκΒ and key IFN-stimulated response elements (ISRE), and FB with many more NFκΒ and STAT-responsive elements than human FB. Thus, the AG129 mouse offers utility in demonstrating changes in FB and FH that, similar to humans, are associated with severe disease, but lack predicted important human-specific and IFN-dependent responses of FB and FH to DENV-infection that are likely to regulate the subtleties of the overall AP response during dengue disease in humans.

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