The immune system is a system of biological structures and
processes within an
organism that protects against
disease. To function properly, an immune system must detect a wide variety of agents, from
viruses to
parasitic worms, and distinguish them from the organism's own healthy
tissue.
Without it, we would all be forced to live in sterile environments, never touching each other, never feeling a spring breeze, never tasting rain. The immune system is that complex operation within our bodies that keeps us healthy and disease-free.
Few systems in nature are as complicated as the human immune system. It exists apart from, and works in concert with, every other system in the body. When it works, people stay healthy. When it malfunctions, terrible things happen.
The main component of the immune system is the lymphatic system. Small organs called
lymph nodes help carry lymph fluid throughout the body. These nodes are located most prominently in the throat, armpit and
groin. Lymph fluid contains lymphocytes and other white blood cells and circulates throughout the body.
The white blood cells are the main fighting soldiers in the body's immune system. They destroy foreign or diseased cells in an effort to clear them from the body. This is why a raised white blood cell count is often an indication of infection. The worse the infection, the more white blood cells the body sends out to fight it.
B cells and T cells are the main kinds of lymphocytes that attack foreign cells. B cells produce antibodies tailored to different cells at the command of the T cells, the regulators of the body's immune response. T cells also destroy diseased cells.
Many diseases that plague mankind are a result of insufficient immunity or inappropriate immune response. A cold, for instance, is caused by a virus. The body doesn't recognize some viruses as being harmful, so the
T cell response is, "Pass, friend," and the sneezing begins.
Allergies are examples of inappropriate immune response. The body is hyper-vigilant, seeing that evil
pollen as a dangerous invader instead of a harmless yellow powder. Other diseases, such as diabetes and AIDS, suppress the immune system, reducing the body's ability to fight infection.