What is immunity? Write a note on the various types of immunity.

Immunity is defined as the ability to resist microorganisms by the production of antibodies by the host or the introduction of antibodies produced externally.

There are two main types of immunity

1. Innate immunity - This is an inborn defense mechanism that the body develops to fight against microorganisms. Example: Skin acts as a barrier and prevents the direct entry of bacteria, viruses, etc.
   
2. Adaptive immunity - Adaptive immunity could be active and passive
   

• Active natural immunity - This is the defense initiated by the human body to fight against infections. Example: The ability of humans to fight off infections by developing antibodies.
  
• Active artificial immunity - This type of immunity is achieved when antigens are introduced to induce the immune system to develop their own antibodies and it takes time. Example: Vaccines are an example of this type of immunity.
  
• Passive natural immunity - This type of immunity is acquired when the antibodies are passed from one person to another by natural means. Example: Antibodies are passed from the mother to the baby through breast milk.
• Passive artificial immunity - This type of immunity is achieved when the antibodies specific to the infection are developed in other organisms and introduced into the infected patient. Example: monoclonal antibodies.