• 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.