IMMUNITY: 

(1) Definition:

(Ability of individual to resist against the micro-organisms is called immunity).

The capacity to recognize the intrusion (disturbance) of any material foreign to the body and to mobilize cells and cell products to help remove the particular sort (particular types) of foreign material with greater speed and effectiveness" is called immunity.

(a) In animals in addition to physical barriers (skin + mucous membranes).

(b) Phagocytes,

(c) There is a third mechanism, to defend their bodies against the foreign invaders; this is the Immune system.

(2) Components of Immune System:

The components of immune system include the:

(i) Lymphocytes (B and T) and the

(ii) Antibodies which are special type of proteins.

These antibodies are immunoglobulins which are synthesized by vertebrates, in response to antigens; and immobilize it, or sets in motion events that ultimately cause its destruction.

(3) Antigen:

Antigen or immunogen is a foreign substance, often a protein which stimulates the formation of antibodies

(4) Antibodies:

Antibodies are specific proteins i.e. cause the destruction of the antigen, which stimulated their production.

Antibodies are Manufactured:

Antibodies are manufactured in B-Lymphocytes, then secreted into the lymph and blood where they circulate freely.

(5) Cell-Mediated Response:

T-cells recognize antigen then combat micro-organisms and/or effect the rejection of foreign tissues (in case of tissue transplant such as kidneys).

This called cell-mediated response.

(6) Humoral Immune Response:

B-cells recognize antigen and form plasma cell clone.

These plasma cells synthesis and liberate antibodies into the blood plasma and tissue fluid.

Here antibodies attach to the surfaces of bacteria and speed up their phagocytosis, or combine with and neutralize toxins produced by micro-organisms, by producing antitoxins.

This is called humoral Immune response.

When we get vaccination, against a specific disease (antigen), we become immune to that infection or disease.

If we get vaccination against, Polio, Smallpox, measles, mumps etc., once in our life time, we are protected or become immune to that infection in our future life.

(7) Types of Immunity:

(i) Active Immunity:

Most of the vaccines consist of a non-virulent, mutant strains of the poliovirus.

The use of vaccines, which stimulate the production of antibodies in the body, and making a person immune against the disease or infection, is called active immunity.

(a) Artificially Induced Active Immunity:

But this active immunity has been achieved by artificially introducing, antigens in the body, so it is called artificially induced active immunity.

(b) Naturally Induced Immunity or Auto Immune Response:

But, when a person is exposed to an infection (antigen)-becomes ill, and in most cases survives then this immunity, developed against that disease is called naturally induced immunity or auto immune response.

Antiserum is a serum containing antibodies.

(ii) Passive Immunity:

In contrast to active immunity, in which case antigens are introduced to stimulate the production of antibodies, by artificial or natural method; antibodies are injected in the form of antisera, to make a person immune against a disease. This is called passive immunity.

Antigen-Antibody Complexes:

In body, antigen-antibody complexes are formed which are taken up by phagocytes and destroyed.

The patient is spared (treat or afford something) the complications (or possibly death) caused by the infection or venom.

Passive immunity response is immediate, but not long lasting.

Because no time is taken for the production of sufficient level of antibodies, (as antibodies are being injected) and after the level of antibodies is reduced or they are used up-No more antibodies production is there.

Combat Active Infections:

 The method of passive immunization is used to combat active infections of:

(i) Tetanus,                    (ii) Infectious hepatitis,                    (iii) Rabies, 

(iv) Snake bite venom etc.

In the case of snake bite venom passive immunity is produced by the antitoxins-so the serum is called anti-venom serum.

AIDS (Acquired Immune Deficiency Syndrome) is a disease caused by a virus.

Affected suffer deficiency in their immune system of the body, and the immune system collapses.

Thus the AIDS victim often succumbs (die) to a bacterial disease or cancer, that under normal circumstances, the immune system can overcome.

There is no known cure of the disease it can be spread by blood transfusions and by close contact with the infected persons.