T he immune system is what protects us from different types of disease. When an invading bacteria, virus, or other antigen enters the human body, a network of cells move in to attack and destroy the invading substance. This may happen without any side effects to the infected person, or the person may develop side effects from the battle between the immune system and the invader.

Blood cells known as macrophages roam through the body looking for foreign elements. When they find one, they digest it and produce something called peptides. These peptides serve as a marker that identifies the invading substance.

White blood cells (lymphocytes) then bind to the marker to “learn” the shape. The white blood cells seek out more of the substance to destroy it, while sending out a signal to the immune system to build up more forces. A result of this buildup is an increased white blood cell count, which is why doctors test blood to see if any infection is present. If you have an elevated white blood cell count, your immune system has detected an invading infection.

One type of white blood cell, the b-lymphocyte, secretes antibody proteins. The proteins work to destroy the invading antigen. Another type, T-lymphocytes, are white blood cells that “read” the markers and alert the immune system to the presence of an infection. T cells can also destroy invading bodies. There are two types of t cells: the helper T and the killer T.

Antibodies are just what the word sounds like, they are cells designed against a foreign body: anti-body. After a specific antibody is built up in the blood, some cells always remain to identify the invader more rapidly the next time the infection strikes. With viral infections, once the body knows the shape, it will eliminate the virus before it can make the person sick. Measles and mumps are illnesses that you can only get once because the body learns to attack those cells after the first exposure. Colds, flus, and other common illnesses occur over and over because there are so many strains of them. You do not have the same type of cold virus twice. One single white cell can produce 10 million antibodies every hour. At that speed, a recognized virus doesn't have a chance to survive in your system and make you sick.

This system of defense from infections, viruses, toxins, and other contaminants is extremely important to human survival. Without an immune system, you would not survive for very long. Babies born without functioning immune systems have to be kept in sterile rooms to protect them. The simplest infection can spread and kill a person if there is no counterattack from within the body.

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