What is a Complement System?
Complement system consists of series of proteins which
complement or augment the function of the antibodies and augment the
inflammatory reactions.
Where the Complementary proteins are produced?
Complement proteins are produced by the liver or the
hepatocytes, some of the complement proteins are produced in GI mucosa. There
are more 20 proteins among the complement proteins. They can be defined as
inactive proteins or inactive enzymes, which are activated only during inflammatory
reaction and immune mediated reactions.
How Complement System is activated?
As soon as antibody (specially IGG and IGM)) bind with
antigen it undergoes transformational changes and exposes a special domain
which binds and activate the complement system.
Early stage of Complement System
Class of antibody (IGG or IGM ) binds with the antigen which
activate complement protein number 1, once it is activated it hydraulically breaks
down the complement number 2 and 4. Complement number 4 is break down into ‘A’
and ‘B’ and similar break down happens to the complement number 2, ‘A’ and ‘B’ remain
with the bold chain and complements move away. These similar sequences happen to
the complement number C3 and make C5 converters, which has power to break down
C5 and convert into active form.
Late events in Complement System
C5b complex with C5, C6, C7, C8 and C9 make a pentameric pore.
This pore acts as a membrane attacking pore and destroy the physical integrity
of bacterial lipid membrane. This membrane attacking complex is formed as a
result of late events occurred in terminal pathway in complement system. The
whole pathway, activation of the complement system is called classical pathway.
The Role C3b in Complement System
C3b facilitates the phagocytosi of bacteria. Any molecule which facilitate the phagocytosis is called opsonin. The two know opsonin molecules are C3b and IGG