Immunology includes all physical, chemical and biological reactions of the organism against the foreign substances. Immune system is divided into two types: innate immunity and adaptive immunity. Adaptive immunity further divided into two types that is humoral and cell mediated immunity. Immunology is the study of the organs, cells, and chemical components of the immune system. The immune system creates both innate and adaptive immune responses.
The innate response exists in many lower species, all the way up the evolutionary ladder to humans, and it acts through relatively crude means against large classes of pathogens. The adaptive response is unique to vertebrates, reacting to foreign invaders with specificity and selectivity. The immune system must maintain a delicate balance, with potent defensive responses capable of destroying large numbers of foreign cells and viruses while refraining from undue destruction of the host & body. When the immune system cannot mount a sufficient defense of the host, there is an immune deficiency; this is seen in HIV infection and Severe Combined Immunodeficiency. If, on the other hand, the immune system acts too vigorously and begins to attack the host, we have autoimmunity.
