Immunity is defined as the state of resistance or in susceptibility to disease caused by particular microorganisms or their toxic products.


  • Innate immunity
  • Acquired Immunity

Innate immunity

 Innate immunity is the first line of defense against pathogens and response is more general and non-specific.

 Innate immunity includes the external barriers of our body — the first line of defense against pathogens — such as the skin and mucous membranes of the throat and gut.

 Adaptive (acquired) immunity

Immunity which is developed later in life after microbial infection in host is called as Acquired or developed immunity. For example, If an individual is infected with chicken pox virus, he/she become resistant to same virus in later life.

Components of acquired immunity such as Antibodies and T- cells are specific to particular microorganism. Therefore acquired immunity is also known as Specific immunity.

Types of acquired immunity:

  1. Active immunity
  2. Passive immunity

Active Immunity 

Antibodies that develop in a person's own immune system after the body is exposed to an antigen through a disease It is slow and takes time in the formation of antibodies. This type of immunity lasts for a long time.

  • Natural active immunity:- A person who has recovered from an attack of small pox or measles or mumps develops natural active immunity.
  • Artificial active immunity: - Is the resistance induced by vaccines. Examples of vaccines are as follows: MMR, BCG , TAB.

Passive immunity

This type of immunity is “borrowed” from another source, It is not long lasting. For instance, a baby receives antibodies from the mother through the placenta before birth and in breast milk following birth. This passive immunity protects the baby from some infections during the early years of their life.

  • Natural passive immunity: - Is the resistance passively transferred from the mother to the foetus through placenta. IgG antibodies can cross placental barrier to reach the foetus.
  • Artificial passive immunity is the resistance passively transferred to a recipient by administration of antibodies. This is done by administration of hyper-immune sera of man or animals. Serum  contains antibodies. For eg. ATS,AGS,ADS.

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