How can an organism immunized against future infections

Question

How can an organism which once underwent contact with an antigen be immunized against the future infections by similar agent?

Answer 1

This phenomenon is termed as immune memory. Whenever an antigen makes contact for the initial time with cells of humoral immune system, B lymphocytes which are producers of particular immunoglobulins against that antigen multiply and in days manufacture their antibodies. This is termed as primary response. Some of such specific B lymphocytes remain in the circulation for a big time, sometimes throughout the whole life of the individual, and they become the memory cells of immune system. Whenever the body is exposed in the future to similar antigen the production of antibodies will be quicker and more intense as the immune system is already made to react against that antigen. This is termed as the secondary response.