NEET PG Medical – 2018 – Question – 36
Opsonin is
a) C3a
b) C3b
c) C5a
d) C6
Show Answer
Correct Answer – B
Answer: B. C3b
The process of coating a foreign particle targeting & preparing it for phagocytosis process is “Opsonization”. Substances involved are opsonins.
Main opsonins from complement system is C3
Examples of opsonins include:
Antibodies:
- 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
C3: - 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
