Opsonization is a process which enhance the efficiency of the phagocytic cells and trigger the process of phagocytosis. This process involves specific antimicrobial agents (mainly some proteins like antibodies etc) which are termed as opsonin. Opsonization is one of the vital part of immunology.
Opsonin: The biomolecules that binds to the surface of the pathogen and increases their susceptibility to phagocytosis, are known as opsonin. They help to make the pathogen easily recognizable to the phagocytic cell. Through this place a vital role in our immune system. Opsonin are antimicrobial protein which are present mainly in the body fluid. There are two main opsonin which play the main role in opsonization process. These are: Complement protein C3b and antibody.
- Complement C3b protein as Opsonin: Complements are a set of plasma protein, which are a vital part of our immune system and plays very important role in destroying pathogen or pathogen infected cells by forming membrane attack complex (MAC). C3b is also a complement protein, which have the ability to bind to microbial surfaces. Phagocytes like macrophages, NK cells bear C3b receptors. C3b bind to the microbial surface and form a complex and then this is recognized by the phagocytic cells and C3b receptor of the phagocytic cell bind with this C3b protein. These whole process triggers the phagocytosis of the microbes and through this C3b protein act as opsonin and facilitate opsonization.
- Antibody as Opsonin: When adaptive immune system recognises a pathogen such as bacteria, then the antibodies which are specific to the pathogen are produced. This antibody binds to the surface of the microbes. Antibody is a Y shaped molecule which have two antigen binding sites and a stalk, which is known as Fc-region. This antibody binds to the microbial surfaces with the antigen binding sites. And phagocytes (macrophages and other phagocytic cells) have receptors for the Fc region of the antibody, called Fc receptor. So, the binding of the Fc receptors with the Fc region of antibody, bound with the antigen facilitate phagocytosis. Though this process of opsonization the antibody acts as opsonin and trigger the process of phagocytosis by helping the phagocytic cells to recognize the specific antigen.