Immune System
The body's defenses against the microorganisms that cause disease.
The immune system provides the human body with protection from the microorganisms that cause disease. Traditionally scientists viewed the immune system as a defensive network that protected the "self from infectious "non-self invaders. In the mid-1990s, some immunologists modified this view of the immune system, creating a new model of the body's immune system that is able to discriminate between beneficial "non-self invaders (food or helpful bacteria) and threatening invaders. One of the leading scientists investigating the functioning of the immune system in the 1990s was Polly Matzinger of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. Matzinger proposed a model of the immune system that responds to invaders only when cells of the body are injured or damaged.
No matter what model is used, immunologists generally agree that the immune systems consists of three lines of defense. The first line is made up of the physical barriers—the skin and mucous membranes—that prevent microorganisms from entering the body. The next line of defense, the innate or non-specific immunity, features responses
The human body is constantly bombarded with microorganisms, including viruses (such as those that cause colds and influenza), bacteria (such as those that cause pneumonia and food poisoning), parasites, and fungi. The immune system efficiently wages a daily battle to rid the body of harmful organisms. When the immune system is unable to function because of injury or damage, the consequences are severe. For instance, Acquired Immune Deficiency Syndrome (AIDS) is caused by a virus—human immunodeficiency virus (HIV)—that attacks a key immune system cell, the helper T-cell lymphocyte. Without these cells, the immune system cannot fight off the harmful microorganisms. Eventually, the person succumbs to infections that a healthy immune system would effortlessly neutralize.
The organs of the immune system a...
Immune system. (Illustration by H...
T Cells, K Cells and the Biology of the Immune System
