This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Opsonic index is the ratio of ? 
Select and explain. 
A. C3b opsonin to antibody opsinin, B. Phagocytic activity of patient to phagocytic activity of normal individual, C. Serum concentration of opsonin in patient to serum concentration in normal individual, D. Complement activity in patient to complement activity in normal individual
B: Phagocytic activity of patient to phagocytic activity of normal individual
Answer: B: Phagocytic activity of patient to phagocytic activity of normal individual 
Explanation: Ans. is 'b' i.e.,Phagocytic activity of patient to phagocytic activity of normal individual The coating of an antigen or paicle (eg - infectious agent) by substances, such as antibodies, complement components and fibronectin facilitate phagocytosis. This is called opsonization.The substance which enhances phagocytosis (causing opsonization) is called opsonin. Two most impoant opsonins are antibodies (IgM, IgG) and complement (C3b).1gM is more effective than IgG in causing opsonization. Other opsonins are serum proteins like fibrinogen, mannose binding lectin and C-reactive proteins.The term 'Opsonic index' is defined as the ratio of of the phagocytic activity of patient's blood for a paicular bacterium to the phagocytic activity of blood of normal individual.It is used to study the progress of resistance during the course of the disease.