What is factor B in the complement system?
Factor B is a component of the alternative pathway of complement. It contains a serine protease (SP) domain, and when activated it provides the catalytic activity of the alternative pathway C3 and C5 convertases.
What is the function of factors B and D in the complement system?
This gene encodes complement factor B, a component of the alternative pathway of complement activation. Factor B circulates in the blood as a single chain polypeptide. Upon activation of the alternative pathway, it is cleaved by complement factor D yielding the noncatalytic chain Ba and the catalytic subunit Bb.
Is BA serine protease a factor?
Factor B and C2 are serine proteases that carry the catalytic sites of the complement C3 and C5 convertases. Their protease domains are activated by conformational changes that occur during convertase assembly and are deactivated upon convertase dissociation.
How is C5 convertase formed?
The classical pathway C5 convertase is composed of the fragments of complement proteins, C4b, C2a produced by cleavage mediated by C1 complex, and C3b produced by cleavage mediated by the classical pathway C3 convertase (C4bC2a).
Does IgM opsonize?
There are no FcµRs on phagocytes, so IgM cannot opsonize in this manner. However, a single molecule of IgM can activate complement through the classical pathway, leading to the deposition of many C3b molecules that can act as opsonins.
Where is factor D produced?
Factor D, also known as adipsin, is a 24 kDa serine protease comprising 228 amino acids (18). Unlike most proteins of the complement system, which are synthesized by the liver and immune cells (19), factor D is predominantly produced by and secreted into the bloodstream by adipocytes (18, 20).
What is the role of factor D?
Factor D fulfills an essential role in the initiation and propagation of the alternative pathway of complement activation and in the amplification loop of C3 activation. Factor D is a serine protease of about 24 kDa that circulates in the blood as a constitutively active enzyme.
What is factor D in the immune system?
Factor D is the enzyme that activates factor B to form the C3 convertase of the alternative pathway. It is a serine protease of MW 24,000 that circulates in plasma in active form. The concentration of factor D in plasma is the lowest of all the complement proteins (1 µg/ml, Table II).
What is the role of C3a c4a and C5a in the immune response?
Role of anaphylatoxins C3a and C5a. Anaphylatoxins C3a and C5a participate in inflammation by interacting and activating immune cells via C3aR and C5aR, respectively. C3a is implicated in the adaptive immunity by inducing monoclonal response from B cells and up-regulation of pro- inflammatory cytokines.
Is opsonization enhanced by IgM?
The pentameric structure of IgM is necessary to enhance opsonization of Bacteroides thetaiotaomicron and Bacteroides fragilis via the alternative complement pathway. Microb Pathog. 1995 Aug;19(2):117-28.