What is the role of complement in the immune response?
Complement is a cascade of proteins that generates immune signals as well as come together to form a membrane attack complex (MAC). Complement proteins C5b with C6-9 create the MAC, which forms a pore in its target, resulting in lysis. Split products generated during this cascade function in several ways:
• C3b and C4b act as opsonins to target phagocytosis of bacterial particles by neutrophils and macrophages. C3b also binds receptors CR1 and CR2 to activate B-cell responses.
• C3a and C5a behave as chemoattractants that recruit neutrophils as well as anaphylatoxins that simulate mast cell and basophil degranulation of histamine, resulting in increased vascular permeability and augmentation of inflammation.