Immune System
Immune System, group of cells, molecules, and organs that act together to defend the body against foreign invaders that may cause disease, such as bacteria , viruses , and fungi . The health of the body is dependent on the immune system’s ability to recognize and then repel or destroy these invaders. IMMUNITY 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. COMPONENTS OF THE IMMUNE SYSTEM The ability of the immune system to mount a response to disease is dependent on m