Immunity: The human body has the ability to resist almost all types of organisms or toxins that tend to damage tissues and organs. This capacity is caused by immunity. (I) Innate immunity – A portion of the immunity results from general processes rather than from processes directed at specific organisms. This is referred to as innate immunity e.g. phagocytosis of bacteria by leucocytes and cells of the tissue macrophage system, destruction of bacteria by acid secretions of the stomach. (II) Acquired immunity – The human body has also the ability to develop extremely powerful specific immunity against individual invading agents such as lethal bacteria, viruses, toxins, and even foreign tissues from other animals. This is called acquired or adaptive immunity.
Acquired immunity is of two types – (a) Humoral immunity – In this type, the body develops circulating antibodies which are globulin molecules having the ability of attacking and invading the foreign agents. (b) Cellular or lymphocytic immunity – This is achieved through the formation of a large number of highly specialised lymphocytes which are specifically sensitised against the foreign agent. These sensitised lymphocytes have the special ability to attack the foreign agent and to destroy it.
Acquired immunity is of two types – (a) Humoral immunity – In this type, the body develops circulating antibodies which are globulin molecules having the ability of attacking and invading the foreign agents. (b) Cellular or lymphocytic immunity – This is achieved through the formation of a large number of highly specialised lymphocytes which are specifically sensitised against the foreign agent. These sensitised lymphocytes have the special ability to attack the foreign agent and to destroy it.