This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Opsonization takes place through: 
Select and explain. 
A. C3a, B. C3b, C. C5a, D. C5b
B: C3b
Answer: B: C3b 
Explanation: Ans. is 'b' i.e., C3b(Ref: Jawetz, 23rd/e, p. 121 - 123)* C3b and C4b are the major opsonins that coat the immune complexes and particulate Ags. Phagocytic cells have receptors for C3b, C4b and are able to bind to complement (C3b, C4b) coated Ags followed by phagocytosis.