Opsonic index is related to -

Ans. is 'a' i.e., Phagocytosis * The coating of an antigen or particle (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 important opsonins are antibodies (IgM, IgG) and complement (C3b). IgM 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 particular 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.