The immune system is a group of cells, molecules, and tissues that help defend the body against diseases and other harmful invaders. The immune system provides protection against a variety of potentially damaging substances that can invade the body. These substances include disease-causing organisms, such as bacteria, fungi, parasites, and viruses.
The first line of defense against foreign invaders is innate immunity. Innate immunity encompasses skin, and the respiratory system, which also contains mucus that traps and destroys invaders. …
