The classical and alternative complement pathways.
C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis. Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb complex (C3bBb3b complex).[1]
C3b's ability to perform these important functions derives from its ability to covalently bind to the surface of invading pathogens within an organism's body. The cleavage of C3 leaves C3b with an exposed thioester bond, allowing C3b to effectively coat and tag foreign cells by covalently binding to hydroxyl (-OH) and amine (-NH2) groups on foreign cell surfaces.[2]
This cleavage can occur via three mechanisms (classical pathway, alternative pathway and lectin pathway) that ultimately lead to the formation of a C3 convertase. Formation of a C3 convertase functions as a positive feedback loop, so as more C3b is cleaved, more C3 convertases are formed, further amplifying the signal on the surface of the microbial invader. This amplification of signal serves as a powerful tool for the immune system in effective clearance of the invading pathogen.
^Liszewski, M. Kathryn; Atkinson, John P. (2015-06-10). "Complement regulator CD46: genetic variants and disease associations". Human Genomics. 9 (1): 7. doi:10.1186/s40246-015-0029-z. PMC 4469999. PMID 26054645.
^Merle, Nicolas S.; Noe, Remi; Halbwachs-Mecarelli, Lise; Fremeaux-Bacchi, Veronique; Roumenina, Lubka T. (2015-05-26). "Complement System Part II: Role in Immunity". Frontiers in Immunology. 6: 257. doi:10.3389/fimmu.2015.00257. ISSN 1664-3224. PMC 4443744. PMID 26074922.
C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b...
pathways that opsonize and kill pathogens. The pathway is triggered when the C3b protein directly binds a microbe. It can also be triggered by foreign materials...
(C4b2b, historically referred C4b2a), which cleaves the C3 protein. The C3b component of the cleaved C3 binds to C3 convertase (C4b2b) to generate C5...
the alternative pathway, C3b binds to Factor B. Factor D releases Factor Ba from Factor B bound to C3b. The complex of C3b(2)Bb is a protease which cleaves...
precursor of some cytokines such as ASP, and C3b serves as an opsonizing agent. Factor I can cleave C3b into C3c and C3d, the latter of which plays a...
innate opsonization include C4b, C3b and iC3b. In the alternative pathway of complement activation, circulating C3b is deposited directly onto antigens...
needed] Although there were several versions of the C3, most were either the C3B and the C3R. A few C3s were approved for float operations.: 59, 198–199 ...
C3b and C4b which are important components for the efficient function of the complement system where they can mediate inflammation, such as when C3b binds...
frequently failed to pre-qualify for races during 1989. It was updated to the C3B for the 1990 season, with the Cosworth DFR being replaced by a Subaru 1235...
Complement receptor type 1 (CR1) also known as C3b/C4b receptor or CD35 (cluster of differentiation 35) is a protein that in humans is encoded by the...
factor I cleaves C3b. Complement receptors on white blood cells are able to bind iC3b, so iC3b functions as an opsonin. Unlike intact C3b, iC3b cannot associate...
activity for Factor I–mediated C3b cleavage, and decay accelerating activity against the alternative pathway C3-convertase, C3bBb. Factor H exerts its protective...
is facilitated by C3b opsonization. Iptacopan acts proximally in the alternative pathway of the complement cascade to control both C3b-mediated EVH and...
Complement factor I, also known as C3b/C4b inactivator, is a protein that in humans is encoded by the CFI gene. Complement factor I (factor I) is a protein...
which had been used the previous season, was extensively modified into the "C3B" specification to be suitable for use with the Subaru 1235, and Bertrand...
gene. CR2 is involved in the complement system. It binds to iC3b (inactive derivative of C3b), C3dg, or C3d. B cells express CR2 receptors on their surfaces...
The properdin promotes the association of C3b with Factor B and provides a focal point for the assembly of C3bBb on a surface. It binds to preformed alternative...
They bear membrane receptors for opsonins, such as IgG and the fragment C3b of complement. They express LCAs (leucocyte common antigens) CD45, CD14,...
proteases. Red blood cells carrying CR1-receptors on their surface may bind C3b-coated immune complexes and transport them to phagocytes, mostly in liver...
the original migration into the Americas. Membership in haplogroups Q and C3b implies Indigenous American patrilineal descent. The micro-satellite diversity...
Phagocytic efficacy can be enhanced by opsonization. Plasma derived complement C3b and antibodies that exude into the inflamed tissue during the vascular phase...
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