The Immune System is a collection of cells and tissues throughout the body that protect us from everyday threats of infection. The main functional cells of the immune system are specific types of white blood cells, called lymphocytes and macrophages. Lymphocytes are made by your body in the thymus and bone marrow and are stored in parts of your body like the lymph nodes, adenoids, and tissue of the small intestine.
Macrophages are cells that engulf foreign invaders.
They're also produced in bone marrow and travel through the body in the circulatory system. Your first line of defense lies outside of the body. These defenses are called nonspecific defenses because they do not involve antibodies. The skin, mucous membranes, hair follicles, and sweat glands are all protectors. Each of these factors restrict the growth of, and protect the body from, microorganisms.