12th Class Biology Microbes in Human Welfare Immunity

Definition : The resistance of the body to occurrence of any disease is known as immunity. Study of the ability of an organism to resist a disease is called immunology.

Development of Immunity : A person may develop immunity in three ways.

(1) Vaccination : It is a technique to develop immunity without infection. Weakened or dead pathogens (attenuated) or parts of pathogens are injected into a person who is required to be made immune. The pathogens given in a vaccine are unable to cause the disease but are sufficient to stimulate the formation of antibodies by the host’s immune system. Often 2 or 3 additional doses are needed to generate adequate immunity. These doses are called booster doses.

(2) Antitoxins : Antibodies that neutralize toxins produced in the body or introduced from outside are, called antitoxins. Bacterial toxins are produced in the body, however antitoxins produced from outside are prepared from snake venom and is used as a remedy for snake bits.

(3) Immunity through Diseases : Some diseases such as mumps, measles, small pox produce a life long immunity. Hence these diseases do not appear again.

Types of Immunity : There are two main types of immunity : Inborn or innate and acquired or adaptive.

(1) Inborn or Innate Immunity : This type of immunity is inherited by the organisms from their parents and protects it from birth throughout life. Examples : Human beings have inborn immunity against distemper (a fatal disease of dogs).

(2) Acquired or Adaptive Immunity : This immunity is acquired in life time. The acquired immunity is of two types : Active or natural and passive or artificial.

(i) Active Immunity : When an organism’s own cells produce antibodies it is called active immunity. It develops when a person suffers from a disease or gets vaccination for a disease.

(ii) Passive Immunity : In passive immunity, the antibodies are produced in some other organisms (e.g. vertebrates) in response to the given antigen. These antibodies are then injected into the human body at the time of need. This is known as inoculation. For example persons infected by rabies, tetanus, Salmonella (causes food poisoning) and snake venom are given the sufficient amount of antibodies so that they can survive.

Passive immunity provides immediate relief, however, active immunity requires some time for the formation of antibodies. There is another form of passive immunity. Nursing mothers transfer antibodies prepared in their body to the infants in their milk. Bottle-fed infants do not get this benefit. After a few weeks, infant’s own immunity system starts working.

Difference between Active Immunity and Passive Immunity