The plasma glycoprotein factor I (C3b/C4b inactivator) is a serine protease that acts as a regulator of the complement C3 cascade. (hindawi.com)
Properdin2
Properdin (Factor P) is the only known positive regulator of complement activation that stabilizes the alternative C3 convertase (C3bBb). (wikipedia.org)
Properdin deficient individuals are sensitive to pyogenic infections. (wikipedia.org)
Opsonin3
The smaller fragment called C3a serves to increase vascular permeability and promote extravasation of phagocytes, while the larger C3b fragment can be used as an opsonin or bind to either type of C3 convertase to form the trimolecular C5 convertase to activate C5 for the membrane attack complex. (wikipedia.org)
Complement factor I is a serine protease present in human plasma that is involved in the degradation of complement protein C3b, which is a major opsonin of the complement system. (hindawi.com)
Complement C3b is the major opsonin of the complement system which facilitates the phagocytosis process by coating antigens (each of the phagocytes expresses a complement receptor such as CR1, CR3, or CR4 that binds C3b, C4b, or C3bi) [ 28 , 29 ]. (hindawi.com)
Fragments2
Cleavage of complement C3 by a free floating convertase, thrombin, plasmin or even a bacterial enzyme leads to formation of C3a and C3b fragments. (wikipedia.org)
Factor I-mediated cleavage of the α chain of C3b liberates 3 fragments with molecular weights of 68 kDa, 43 kDa, and 2 kDa. (hindawi.com)
Pathways1
Activation of the complement system in response to an infection or foreign antigen is achieved via three complement pathways, the classical pathway, which is activated by antigen-antibody complexes, the lectin pathway, which is activated by the interaction of microbial carbohydrates with mannose-binding proteins in the plasma and tissue fluids, and the alternative complement pathway, which is activated by C3b binding to microbial surfaces and to antibody molecules. (hindawi.com)
Microbial1
C3b, the larger fragment, becomes covalently attached to the microbial surface or to the antibody molecules through the thioester domain at the site of complement activation. (wikipedia.org)
Cleavage1
After cleavage and binding to cell surface, the C3b fragment is ready to bind a plasma protein called Factor B. The Factor B (a zymogen) is cleaved by a plasma serine protease Factor D releasing a small fragment called Ba and generating a larger fragment called Bb that remains attached to C3b. (wikipedia.org)
Molecules1
Since C3 convertases cleave C3 to produce C3b which can then form an additional C3 convertase through the alternative pathway, this is a potential mechanism of signal amplification in the complement cascade resulting in the deposition of large numbers of C3b molecules on the surface of activating particles, enabling opsonisation and acute local inflammation. (wikipedia.org)
Classical pathway2
In the classical pathway, this is by sequential proteolytic activation of proteins within the C1 complex (C1q, C1r, C1s) in response to binding to CRP or immunoglobulin, and in the lectin pathway it is driven by mannose binding lectin and its associated serine proteases (MASPs, particularly MASP2 but also MASP1). (wikipedia.org)
C4 binding protein (C4BP) interferes with the assembly of the membrane-bound C3 convertase of the classical pathway. (wikipedia.org)
Membrane protein1
It is a membrane protein and regulates also C5 convertase of the classical and alternative pathway. (wikipedia.org)
System4
C3 convertase (C4bC2b, formerly C4b2a) belongs to family of serine proteases and is necessary in innate immunity as a part of the complement system which eventuate in opsonisation of particles, release of inflammatory peptides, C5 convertase formation and cell lysis. (wikipedia.org)
Immune system abnormalities may be caused partly by complement system factor I deficiency. (hindawi.com)
The complement system comprises a group of proteins which, when activated, provide one of the first lines of defence by promoting lysis and the removal of invading microbes. (hindawi.com)
It has been shown by comparison with healthy control children that several differentially expressed proteins are related to the complement system in children with ASD [ 22 ]. (hindawi.com)
Acts1
DAF acts on C2b and Bb and dissociates them rapidly from C4b and C3b - thereby preventing the assembly of the C3 convertase. (wikipedia.org)
Factor4
Deficiency in factor I activity is associated with an increased incidence of infections in humans. (hindawi.com)
In this paper, we show that the mean level of factor I activity in the ASD group is significantly higher than in the control group of typically developed and healthy children, suggesting that high activity of complement factor I might have an impact on the development of ASD. (hindawi.com)
Factor I cleaves C3b and C4b in a reaction, where fI is dependent on various cofactors, such as factor H, C4b-binding protein CR1 and membrane cofactor protein (MCP) [ 26 ]. (hindawi.com)
Factor I deficiency can be conferred by a C3 deficiency, since this also increases susceptibility to pyogenic infections by Neisseria meningitides, Haemophilus influenza, and Streptococcus pneumonia and increases the incidence of immune complex diseases due to impaired complement-mediated function [ 30 ]. (hindawi.com)
Cleave2
Since C3 convertases cleave C3 to produce C3b which can then form an additional C3 convertase through the alternative pathway, this is a potential mechanism of signal amplification in the complement cascade resulting in the deposition of large numbers of C3b molecules on the surface of activating particles, enabling opsonisation and acute local inflammation. (wikipedia.org)
This heterodimer can cleave and inactivate the complement components C4b and C3b, and it prevents the assembly of the C3 and C5 convertase enzymes. (nih.gov)
Alternative pathways1
C3 is the most important central molecule in the complement system because both the classic and alternative pathways activate it, and its activation products mediate opsonization and anaphylactic activity and activate the terminal pathway. (medscape.com)
Deficiency3
Defects in this gene cause complement factor I deficiency, an autosomal recessive disease associated with a susceptibility to pyogenic infections. (nih.gov)
Complete C4 deficiency also may manifest with infection or may not be associated with any symptoms. (medscape.com)
This is the most common inherited complement deficiency. (medscape.com)
Convertase7
C3 convertase (C4bC2b, formerly C4b2a) belongs to family of serine proteases and is necessary in innate immunity as a part of the complement system which eventuate in opsonisation of particles, release of inflammatory peptides, C5 convertase formation and cell lysis. (wikipedia.org)
The smaller fragment called C3a serves to increase vascular permeability and promote extravasation of phagocytes, while the larger C3b fragment can be used as an opsonin or bind to either type of C3 convertase to form the trimolecular C5 convertase to activate C5 for the membrane attack complex. (wikipedia.org)
Cleavage of complement C3 by a free floating convertase, thrombin, plasmin or even a bacterial enzyme leads to formation of C3a and C3b fragments. (wikipedia.org)
Properdin (Factor P) is the only known positive regulator of complement activation that stabilizes the alternative C3 convertase (C3bBb). (wikipedia.org)
It is a membrane protein and regulates also C5 convertase of the classical and alternative pathway. (wikipedia.org)
DAF acts on C2b and Bb and dissociates them rapidly from C4b and C3b - thereby preventing the assembly of the C3 convertase. (wikipedia.org)
C4 binding protein (C4BP) interferes with the assembly of the membrane-bound C3 convertase of the classical pathway. (wikipedia.org)
Cascade1
From NCBI Gene: This gene encodes a serine proteinase that is essential for regulating the complement cascade. (nih.gov)
Components1
Congenital complement deficiencies involve all of the complement components and most of the regulatory components. (medscape.com)