Immune System: Types of Immunity with functions and Disease | Biology

“The capacity to recognize the foreign material to the body and mobilize cells and cell products to remove this foreign material with greater speed and effectiveness is called Immunity.” Basically, the immune system is the body’s defense against different infectious organisms and other invaders.Immune-system-(immunity)

There are three mechanisms in animals to define the body against foreign invaders. These are:

  • Physical barriers: like skin and mucous members
  • Phagocytes
  • Immune system

Immune system

The immune system is composed of lymphocytes and antibodies.


There are two types of lymphocytes.

·         T lymphocytes:

They recognize the antigen and combat with them. The antigen may be any foreign object like microorganisms, foreign tissue in case of tissue transplant. So T lymphocytes shows cell mediated response.

·          B lymphocytes

They recognize the antigen and form plasma cell cone. These plasma cell cones synthesize liberate antibodies in to the blood plasma and tissue fluid. These antibodies attract the surface of the bacteria and speed up the phagocytosis. Sometimes, the microorganisms produces toxin. The antibodies produced antitoxin and neutralize these toxins. This is called humoral immunity response.

The people are vaccinated against the antigen of the specific diseases like polio, Smallpox, Measles and Mumps. So the persons produced the antibodies against the antigen and become immune to the infection of this specific disease in the future.


The antibodies are the special type of protein called immunoglobulin. The vertebrates produce the antibodies in response to the antigens. The antigen or immunogen is a foreign substance (often protein) which stimulates the synthesis of antibody formation.

The antibodies immobilize the antigen. It ultimate causes the destruction of antigen. The antibodies are specific. These destroy the only antigen which simulates the formation of that antigen. Antibodies are synthesized in B- lymphocytes. Then these are secreted into the lymph and blood. These circulate freely in the lymph and blood.

Structure of antibody:

An antibody molecule consists of four polypeptide chains: two identical light chains and two identical heavy chains. These chains are linked by disulfide (S-S). Each chain of the antibody has two parts.

  • Variable amino acid sequences (V): These sequences determine which antigen will bind with the particular anti body.
  • Constant amino acid sequences (C): These chains are same in all the antibodies in one class.

Some time they are multiple copies of the antigenic molecule on the foreign cell, surface. So large antigen-antibody complexes are formed.

Types of Immunity in Immune system:

Following are two types of Immunity:

Active Immunity:

“The use of vaccines or antigens, which simulates the production of antibodies in the body and makes the person immune against the disease or infection, is called active immunity.” Most of the vaccines consist of the non-virulent, mutant strains of virus. There are two types of active immunity:

  • Artificially induced active immunity: The active immunity is achieved by artificially introducing antigens in the body. So it is called artificially active immunity.
  • Naturally induced active immunity or auto immune response: Sometimes the person is inflected by antigen and he becomes ill. In most cases he survives and developed immunity against that diseases. It is called natural induced immunity or auto immune response.

Passive Immunity:

“The injection of antibody in the form of antisera for making a person immune against a diseased is called passive immunity.” Antigen antibodies complex are formed within the body. This complex is destroyed by the phagocytes. So the patient is saved from complications and sometime from the death.

During the infection the cell not given time for the production of sufficient level of antibodies and antibodies injected artificially. Passive immunity response is immediate. It is not long lasting. After sometimes, the antibodies are used in the level of antibodies is decreased. The antibodies are not left in the body.

The methods of passive immunization is used to combat active infections like tetanus, infections hepatitis, rabies, snake bite venom etc. antitoxin produced the passive immunity in the snack bite venom. So the antitoxin serum is called antivenom serum.

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