• All around us is teeming with disease-causing micro-organisms.

  • Survival depends on the defense mechanisms that establish a state of immunity against infection.

  • These defense mechanisms against disease may be either



innate immunity or

adaptive immunity


Innate immunity


  • provides first line of defense (usually clear infections without need for adaptive immunity).

  • present in an individual from birth, i.e., does not require prior contact with an infectious agent in order to become active.

  • has both nonspecific and specific components.