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Once cleaved C3b can either generate C3 or C5 convertases, as mentioned above, or else covalently bind to the microbial surface, tagging the cell for phagocytosis in a process known as opsonization. Additionally, C3b molecules can attach to the Fc regions of antigen-bound antibodies leading to phagocytosis or movement to the liver, where the ...
C4b-binding protein inhibits the haemolytic function of cell-bound C4b. C4b-binding protein and C3b inactivator control the C3 convertase of the classical pathway in a similar way to that described for β1H and C3b inactivator in the alternative pathway. [8] C3b has different binding site for C3bINA, β1H, factor B and properdin.
The C5-convertase of the alternative pathway consists of (C3b) 2 BbP (sometimes referred to as C3b 2 Bb). After the creation of C5 convertase (either as (C3b) 2 BbP or C4b2a3b from the classical pathway), the complement system follows the same path regardless of the means of activation (alternative, classical, or lectin). C5-convertase cleaves ...
The membrane attack complex creates a pore on the target cell's membrane, inducing cell lysis and death. [2] [3] The classical complement pathway can also be activated by apoptotic cells, necrotic cells, and acute phase proteins. [1] [3] [4]
12266 Ensembl ENSG00000125730 ENSMUSG00000024164 UniProt P01024 P01027 RefSeq (mRNA) NM_000064 NM_009778 RefSeq (protein) NP_000055 NP_033908 Location (UCSC) Chr 19: 6.68 – 6.73 Mb Chr 17: 57.51 – 57.54 Mb PubMed search Wikidata View/Edit Human View/Edit Mouse Complement component 3, often simply called C3, is a protein of the immune system that is found primarily in the blood. It plays a ...
Cell-bound C3 and C5 convertase differ in their C3b requirement. C3-convertase (C3bBb) need only one molecule of C3b to form, whereas two or more C3b are required for generation of C5 convertase (C3bBb). It means, when C3b is randomly distributed on the surface of a cell, only C3 convertase activity appears after addition of Factors B and D.
Factor H can bind C3b much more easily in the presence of sialic acid, which is a component of most cells in the human body; conversely, in the absence of sialic acid, factor B can bind C3b more easily. This means that if C3b is bound to a "self" cell, the presence of sialic acid and the binding of factor H will prevent the complement cascade ...
The active subunit Bb is a serine protease that associates with C3b to form the alternative pathway C3 convertase. Bb is involved in the proliferation of preactivated B lymphocytes, while Ba inhibits their proliferation. This gene localizes to the major histocompatibility complex (MHC class III) region on chromosome 6. This cluster includes ...