Opsonization : Defination, Opsonins and Machanism

Opsonization is a process which enhances the efficiency of phagocytosis by phagocytic cells. This process involves specific antimicrobial proteins which are termed as Opsonins

  These antimicrobial proteins are present in our body fluids.
Phagocytes such as Macrophages and Neutrophils have receptors for these opsonins on their plasma membrane.  

Opsonins have ability to bind the microbial surface. They coat the microbial surface and this coating increases the number and kind of binding sites on the microbial surface.
In Greek, "opson" means to prepare for eating.

Opsonins coat the microbial surface. Phagocytes have specific receptors for these options.
Optionization helping in the phagocytosis process.

Once opsonins coat the microbial surface, this coating makes the recognition and destruction of the invader more efficient.
This is because the number of binding sites and type of binding sites has increased.

Definition of Opsonization

The process of coating pathogens to promote phagocytosis is called optinization. The proteins which perform this function are called Opsonins.

Types of Opsonins

There are two main options in human body which are
  1). Complement C3b 
  2). Antibody 

Compliment C3b as Opsonin

  Complement or Complement system is a set of plasma proteins. They help in elimination of microbes.

• C3b is a complement proteins which has ability to bind microbial surfaces.
• Phagocytes bear C3b receptors.
• Once the C3b protein coat the microbial surface, The C3b receptors find these C3b proteins and triggers phagocytosis of the microbe.

Antibody as opsonin

Antibody is a part of adaptive immune system. 

When adaptive immune system recognizes a pathogen such as a bacteria, antibody specific to bacteria or that pathogen are produced. 

These antibodies bind to the surface of microbes.

Antibody is a y-shaped molecule and two arms of that Y form the antigen binding site (FB) and stalk is known as FC region.
These antibody binds to the microbial surface with their antigen binding arms.

Phagocytes has a receptor for the FC region of the antibody.
• So first the antibody binds to the antigen on the bacterial cell wall via antigen binding site.
• Then FC receptors of the phagocyte bind the FC region of the antibodies which facilitate phagocytosis.

Opsonins function as a bridge between pathogens and the phagocytes. Opsonization is the process which enhances the phagocytic ability of a phagocyte. 

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