Immunization is the development of resistance against a pathogen. It is carried out through vaccination. Principle of vaccination. Vaccination introduces a harmless antigen of a pathogen into the body. Our immune system develops some antibodies and memory lymphocytes against the pathogen. When the actual pathogen
happens to enter the body, the immune system recognizes its antigen through memory cells. The memory cells induce large scale synthesis of cytotoxic and antibody producing lymphocytes to eliminate the pathogen.