Immunity: Innate and Adaptive
. Most animals have systems that resist disease. The disease resistance provided by these systems is called immunity. There are two types of immunity: innate and adaptive. Innate, or nonspecific, immunity is the body’s first, generalized line of defense against all invaders. Innate immunity is furnished by barriers such as skin, tears, mucus, and saliva, as well as by the rapid inflammation of tissues that takes place shortly after injury or infection. These innate immune mechanisms hinder the entrance and spread of disease but can rarely prevent disease completely. If an invader gets past this first line of defense, the cells, molecules, and organs of the immune system develop specifically tailored defenses against the invader. The immune system can call upon these defenses whenever this particular invader attacks again in the future. These specifically adapted defenses are known as adaptive, or specific, immunity. Adaptive immunity has four distinguishing properties: First, it respon...