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Complement C4a
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D015934 |
[The smaller fragment formed when complement C4 is cleaved by COMPLEMENT C1S. It is an anaphylatoxin that causes symptoms of immediate hypersensitivity (HYPERSENSITIVITY, IMMEDIATE) but its activity is weaker than that of COMPLEMENT C3A or COMPLEMENT C5A.
] |
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Complement C4b
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D015935 |
[The large fragment formed when COMPLEMENT C4 is cleaved by COMPLEMENT C1S. The membrane-bound C4b binds COMPLEMENT C2A, a SERINE PROTEASE, to form C4b2a (CLASSICAL PATHWAY C3 CONVERTASE) and subsequent C4b2a3b (CLASSICAL PATHWAY C5 CONVERTASE).
] |
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Complement C4b-Binding Protein
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D050716 |
[A serum protein that regulates the CLASSICAL COMPLEMENT ACTIVATION PATHWAY. It binds as a cofactor to COMPLEMENT FACTOR I which then hydrolyzes the COMPLEMENT C4B in the CLASSICAL PATHWAY C3 CONVERTASE (C4bC2a).
] |
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Complement C5
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D003182 |
[C5 plays a central role in both the classical and the alternative pathway of COMPLEMENT ACTIVATION. C5 is cleaved by C5 CONVERTASE into COMPLEMENT C5A and COMPLEMENT C5B. The smaller fragment C5a is an ANAPHYLATOXIN and mediator of inflammatory process. The major fragment C5b binds to the membrane initiating the spontaneous assembly of the late complement components, C5-C9, into the MEMBRANE ATTACK COMPLEX.
] |
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Complement C5 Convertase, Alternative Pathway
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D051566 |
[A serine protease that cleaves multiple COMPLEMENT C5 into COMPLEMENT C5A (anaphylatoxin) and COMPLEMENT C5B in the ALTERNATIVE COMPLEMENT ACTIVATION PATHWAY. It is the complex of ALTERNATIVE PATHWAY C3 CONVERTASE (C3bBb) with an additional COMPLEMENT C3B, or C3bBb3b.
] |
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Complement C5 Convertase, Classical Pathway
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D051577 |
[A serine protease that cleaves multiple COMPLEMENT 5 into COMPLEMENT 5A (anaphylatoxin) and COMPLEMENT 5B in the CLASSICAL COMPLEMENT ACTIVATION PATHWAY. It is a complex of CLASSICAL PATHWAY C3 CONVERTASE (C4b2a) with an additional COMPLEMENT C3B, or C4b2a3b.
] |
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Complement C5a
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D015936 |
[The minor fragment formed when C5 convertase cleaves C5 into C5a and COMPLEMENT C5B. C5a is a 74-amino-acid glycopeptide with a carboxy-terminal ARGININE that is crucial for its spasmogenic activity. Of all the complement-derived anaphylatoxins, C5a is the most potent in mediating immediate hypersensitivity (HYPERSENSITIVITY, IMMEDIATE), smooth MUSCLE CONTRACTION; HISTAMINE RELEASE; and migration of LEUKOCYTES to site of INFLAMMATION.
] |
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Complement C5a, des-Arginine
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D015937 |
[A derivative of complement C5a, generated when the carboxy-terminal ARGININE is removed by CARBOXYPEPTIDASE B present in normal human serum. C5a des-Arg shows complete loss of spasmogenic activity though it retains some chemotactic ability (CHEMOATTRACTANTS).
] |
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Complement C5b
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D050776 |
[The larger fragment generated from the cleavage of C5 by C5 CONVERTASE that yields COMPLEMENT C5A and C5b (beta chain + alpha' chain, the residual alpha chain, bound by disulfide bond). C5b remains bound to the membrane and initiates the spontaneous assembly of the late complement components to form C5b-8-poly-C9, the MEMBRANE ATTACK COMPLEX.
] |
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Complement C6
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D003183 |
[A 105-kDa serum glycoprotein with significant homology to the other late complement components, C7-C9. It is a polypeptide chain cross-linked by 32 disulfide bonds. C6 is the next complement component to bind to the membrane-bound COMPLEMENT C5B in the assembly of MEMBRANE ATTACK COMPLEX. It is encoded by gene C6.
] |
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Complement C7
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D003184 |
[A 93-kDa serum glycoprotein encoded by C7 gene. It is a polypeptide chain with 28 disulfide bridges. In the formation of MEMBRANE ATTACK COMPLEX; C7 is the next component to bind the C5b-6 complex forming a trimolecular complex C5b-7 which is lipophilic, resembles an integral membrane protein, and serves as an anchor for the late complement components, C8 and C9.
] |
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Complement C8
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D003185 |
[A 150-kDa serum glycoprotein composed of three subunits with each encoded by a different gene (C8A; C8B; and C8G). This heterotrimer contains a disulfide-linked C8alpha-C8gamma heterodimer and a noncovalently associated C8beta chain. C8 is the next component to bind the C5-7 complex forming C5b-8 that binds COMPLEMENT C9 and acts as a catalyst in the polymerization of C9.
] |
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Complement C9
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D003186 |
[A 63-kDa serum glycoprotein encoded by gene C9. Monomeric C9 (mC9) binds the C5b-8 complex to form C5b-9 which catalyzes the polymerization of C9 forming C5b-p9 (MEMBRANE ATTACK COMPLEX) and transmembrane channels leading to lysis of the target cell. Patients with C9 deficiency suffer from recurrent bacterial infections.
] |
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Complement Factor B
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D011415 |
[A glycine-rich, heat-labile serum glycoprotein that contains a component of the C3 CONVERTASE ALTERNATE PATHWAY (C3bBb). Bb, a serine protease, is generated when factor B is cleaved by COMPLEMENT FACTOR D into Ba and Bb.
] |
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Complement Factor D
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D011416 |
[A serum protein which is important in the ALTERNATIVE COMPLEMENT ACTIVATION PATHWAY. This enzyme cleaves the COMPLEMENT C3B-bound COMPLEMENT FACTOR B to form C3bBb which is ALTERNATIVE PATHWAY C3 CONVERTASE.
] |
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Complement Factor H
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D017242 |
[An important soluble regulator of the alternative pathway of complement activation (COMPLEMENT ACTIVATION PATHWAY, ALTERNATIVE). It is a 139-kDa glycoprotein expressed by the liver and secreted into the blood. It binds to COMPLEMENT C3B and makes iC3b (inactivated complement 3b) susceptible to cleavage by COMPLEMENT FACTOR I. Complement factor H also inhibits the association of C3b with COMPLEMENT FACTOR B to form the C3bB proenzyme, and promotes the dissociation of Bb from the C3bBb complex (COMPLEMENT C3 CONVERTASE, ALTERNATIVE PATHWAY).
] |
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Complement Factor I
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D017244 |
[A plasma serine proteinase that cleaves the alpha-chains of C3b and C4b in the presence of the cofactors COMPLEMENT FACTOR H and C4-binding protein, respectively. It is a 66-kDa glycoprotein that converts C3b to inactivated C3b (iC3b) followed by the release of two fragments, C3c (150-kDa) and C3dg (41-kDa). It was formerly called KAF, C3bINF, or enzyme 3b inactivator.
] |
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Complement Fixation Tests
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D003168 |
[Serologic tests based on inactivation of complement by the antigen-antibody complex (stage 1). Binding of free complement can be visualized by addition of a second antigen-antibody system such as red cells and appropriate red cell antibody (hemolysin) requiring complement for its completion (stage 2). Failure of the red cells to lyse indicates that a specific antigen-antibody reaction has taken place in stage 1. If red cells lyse, free complement is present indicating no antigen-antibody reaction occurred in stage 1.
] |
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Complement Hemolytic Activity Assay
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D015941 |
[A screening assay for circulating COMPLEMENT PROTEINS. Diluted SERUM samples are added to antibody-coated ERYTHROCYTES and the percentage of cell lysis is measured. The values are expressed by the so called CH50, in HEMOLYTIC COMPLEMENT units per milliliter, which is the dilution of serum required to lyse 50 percent of the erythrocytes in the assay.
] |
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Complement Inactivating Agents
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D051056 |
[Compounds that negatively regulate the cascade process of COMPLEMENT ACTIVATION. Uncontrolled complement activation and resulting cell lysis is potentially dangerous for the host.
] |
