![]() ![]() C5a diffuses away but C5b is stabilized by binding C6. C3b binds to the microbial surface or to the convertase itself.Ĭ3b when binds to C3 convertase forms C4bC2aC3b ( C5 convertase) which activates C5.Ĭ5 convertase cleaves C5 into C5a and C5b. One molecule of C4b2a can cleave a large number of C3 molecules. The C4b2a complex is also known as C3 convertase as this converts C3 into an active form by separating C3a and C3b. C2a binds C4b forming the C4b2a complex whereas C2b goes away. Now, C4b attracts C2 which is also cleaved into C2a and C2b. ![]() C4a goes away whereas activated C4b attaches to the target surface near C1q. The immune complex bound to C1 calls another protein C4 which is cleaved into C4a and C4b. C1r and C1s are proteases that help to cleave C4 and C2. C1q binds to the antigen-bound antibody (Fc portion). Hence, the antibody activates the complement system only when bound to an antigen.Ĭ1 is a large, multimeric, protein complex composed of one molecule of C1q and two molecules each of C1r and C1s subunits. This induces conformational changes in the Fc portion of the antibody which exposes a binding site for C1 protein. When an antigen enters the body, the antibody (IgM/IgG) binds to it. The classical pathway begins with the formation of the antigen-antibody complex (immune complex). ![]() This occurs through three pathways the classical pathway, activated by antigen-antibody reaction, the alternative pathway, activated on microbial cell surfaces, and the mannose-binding lectin pathway, activated by a plasma lectin that binds to mannose residues on microbes. However, all the pathways form enzyme complexes C3 convertase, which cleaves C3 into C3a and C3b and the C5 convertase, which cleaves C5 into C5a and C5b.C3b, thus formed, binds C3 convertase to form C5 convertase.Ĭ5 convertase, generated by the alternative, classical, or lectin pathway, initiates the activation of late components of the complement system to form a membrane attack complex (MAC) and ultimately kills the pathogen. The early step of complement system varies in different pathways.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |