The immune response is how the body defends itself from identified harmful and foreign substances such as bacteria and viruses.
This is divided into two major divisions: the innate immune response pertains to the nonspecific biological reactions which are already present at birth such as cough reflex, trapping of small particles by the mucus, and the protective function of the skin; and acquired immune response develops when the memory of the immune response cells become more sensitized towards an antigen; this may then be manifested as an allergic reaction. Acquired immune response is the basic priniciple behind immunization. This works by introducing a small amount of the disease bacteria into the body to create an immune response which allows a person to resist the those antigens when exposed. This is the method that has almost eradicated diseases like smallpox and polio which have histories of epidemics with a high mortality rate.