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Scheme of the complement system. The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. [1]
Both enzymes, C4b2b3b and C3bBbC3b, are unstable and undergo decay dissociation with a half-life at 37 °C of approximately 1.5 - 3 min. [1] The properdin stabilizes the alternative pathway C5 convertase of which half-life is at 37 °C 10 - 34 min. [2] [3] In contrast, the fluid phase C5 convertase CVFBb is stable (half-life at 37 °C = 7 h). [10]
The classical complement pathway is one of three pathways which activate the complement system, which is part of the immune system. The classical complement pathway is initiated by antigen-antibody complexes with the antibody isotypes IgG and IgM. [1] [2]
Structure of mannose in its α-D mannopyranose form. Mannan is a polymer of mannose.. The lectin pathway or MBL pathway is a type of cascade reaction in the complement system, similar in structure to the classical complement pathway, [1] in that, after activation, it proceeds through the action of C4 and C2 to produce activated complement proteins further down the cascade.
Complement component 5 is a protein that in humans is encoded by the C5 gene. [5] Complement component 5 is involved in the complement system. It is cleaved into C5a and C5b: C5a plays an important role in chemotaxis. [6] C5b forms the first part of the complement membrane attack complex. Deficiency is thought to cause Leiner's disease.
The C1q domain is a conserved protein domain. C1q is a subunit of the C1 enzyme complex that activates the serum complement system.C1q comprises 6 A, 6 B and 6 C chains.These share the same topology, each possessing a small, globular N-terminal domain, a collagen-like Gly/Pro-rich central region, and a conserved C-terminal region, the C1q domain. [2]
C5a is a protein fragment released from cleavage of complement component C5 by protease C5-convertase into C5a and C5b fragments. C5b is important in late events of the complement cascade, an orderly series of reactions which coordinates several basic defense mechanisms, including formation of the membrane attack complex (MAC), one of the most basic weapons of the innate immune system, formed ...
The alternative pathway is a type of cascade reaction of the complement system and is a component of the innate immune system, a natural defense against infections. The alternative pathway is one of three complement pathways that opsonize and kill pathogens. The pathway is triggered when the C3b protein directly binds a microbe. It can also be ...