Immunization against antigen

Question

How organism which had once undergone contact with an antigen can be immunized against the future infections by the same agent?

Answer 1

This mechanism is known as immune memory. Whenever an antigen forms contact for first time with the cells of humoral immune system, B lymphocytes which are producers of the specific immunoglobulins against that antigen multiply and in days synthesize their antibodies. This is termed as primary response. Some of these specific B lymphocytes stay in the circulation for long time, sometimes during the entire life of the individual, and they become memory cells of the immune system. Whenever the body is exposed in future to the same antigen production of the antibodies will be faster and more intense as the immune system is already prepared to react against that antigen. This is known as the secondary response.