Question

Explain the various types of acquired immunity.

Answer 1

The resistance that an individual acquires during life is known as Acquired immunity or Adaptive or Specific immunity. It involves the formation of antibodies in the body, which neutralize the antigens. Acquired immunity is of two types Active and Passive.

i. Active immunity: It is the resistance developed by individuals as a result of an antigenic stimulus (exposure to antigen). It also known as “Adaptive immunity”. Active immunity may be natural or artificial.

1. Natural Acquired Active immunity: Immunity acquired due to infection is called natural active immunity. It is developed after entry of pathogens in the body. It is long-lasting immunity. e.g. Person who has recovered from attack of measles develops natural acquired active immunity to measles, for the life time.
2. Artificial Acquired Active immunity: It is the resistance induced by vaccines. Vaccine is introduced into the body to stimulate the formation of antibodies by the immune system. e.g. Polio vaccine, BCG vaccine etc. such immunity may be temporary or permanent.

ii. Passive immunity: Passive immunity is acquired when ready-made antibodies are received by the body cells. i.e. Body cells do not take any active part in the production of immunity. Passive immunity can be acquired either naturally or artificially. 

1. Natural Acquired Passive immunity: Before birth maternal antibodies are transferred from mother to foetus through placenta. After birth, antibodies are transferred from mother to infant through colostrum (first milk of mother) and continue throughout the period of breast feeding. The antibodies received by baby from mother remain in the body for a short time. Therefore, natural acquired passive immunity is short lived. 
2. Artificially Acquired Passive immunity: This immunity is developed by injecting previously prepared antibodies using serum from humans or animals. e.g. Antibodies obtained from hyper immunised horses are injected to humans against rabies pathogens. It is short lived.