What is Pathology - What happens when the complement system is activated?
There are four major biological functions of complement activation:
a)Bacterial Opsonization: This is mostly performed by pieces like C3b. C3 receptors are found on neutrophils and macrophages, allowing them to adhere tightly to opsonized bacteria and phagocytize them.
b) Chemotaxis: Complement fragments like C5a and intermediate complexes like C567 recruit neutrophils to inflammatory sites.
c) Anaphylatoxic action: Complement fragments such as C5a are known as anaphylatoxins because they connect to mast cells and cause them to release histamine, resulting in increased blood vessel permeability. This is most common in anaphylactic shock, although it can also happen in other types of localised inflammatory edoema.
d) Cytolysis: MAC, which is made up of aggregated complement proteins C5 to C9, enters the plasma membrane of target cells and causes them to lyse. Immune hemolytic anaemia is a common cause of this.
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