Opsonin isC3b Answer: B. C3b

Opsonin is
a) C3a
b) C3b
c) C5a
d) C6
Correct Answer - B
Answer: B. C3b
The process of coating a foreign particle targeting & preparing it for
phagocytosis process is “Opsonization”. Substances involved are
Main opsonins from complement system is C3
Examples of opsonins include:
IgG and IgA
Components of the complement system:
C3b, C4b, and iC3b
Mannose Binding Lectin (MBL):
Initiates the formation of C3b
Membrane Attack Complex (MAC)
Includes C5b, C6, C7, C8 & polymeric C9
Opsonization & complement proteins:
Mainly C3b, iC3b & C4b
Most abundant protein of all complementary proteins,
Cleaves into C3a and C3b
C3a -
Binds and activates mast cells & basophils, release histamine.
C3b -
Most critical component in both classical & alternative pathway
C3b attaches to bacterial surfaces for opsonization by phagocytes