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Immune System: Introduction

Every day, your body is exposed to thousands of potential disease-causing organisms, or pathogens. These pathogens are everywhere, on your hands, in the air, even on your pillow! Thinking about how many pathogens are out there, it’s amazing that we don’t get sick more often. How does your body work to stay healthy with everyday exposure to these potential pathogens?

Your immune system! When your body fights a cold or an infection, it is your immune system at work. All animals, from fruit flies to humans, have some type of immune system to keep them healthy.

How does it work?
The immune system works by identifying foreign invaders in the body- this is called recognizing “self from non-self”. Special immune cells in the body are able to react to foreign invaders that don’t belong in the body to get rid of them or to neutralize them. They patrol the body constantly in their search for organisms that may cause disease. They have the ability to communicate through chemical signals and by cell–to-cell contact.

Helper T cell makes contact with an antigen presenting cell.  The T cell then releases chemical signals.
Immune cells communicate with each other through cell-to-cell contact. Cells touch using surface receptors-this can cause a cell to carry out a function like seeking out invading bacteria. Another way cells communicate is by using chemicals (like hormones and cytokines) that are produced by different types of cells. Chemicals travel throughout the body via blood and tissues. They bind to surface receptors on certain cells to deliver a signal.

This ability for recognition is important because you don’t want these immune cells to attack your own body. When the immune system is not working the way it should and cannot identify (or “see”) the difference between self and what is non-self, disease results- this is called “auto immunity”. Auto immunity causes damage to the body’s organs and tissues.

Antibodies released by a plasma cell attacking  tissue cells.
When the immune system is not working the way it should, it attacks its own body cell and tissues instead of foreign invaders like bacteria and viruses. Auto immunity causes damage to the body’s organs and tissues. This cartoon shows an immune cell making antibodies that will result in damage to the tissue cells.

Foreign “invaders” are usually bacteria, fungi, or viruses that may cause disease or infection. These microorganisms are all around us as a normal part of our environment, and only cause problems in certain situations, for example if your immune system is not working normally (immune suppression), if the microorganisms are too great in number, or if they are especially pathogenic (disease-causing).

Your skin provides an effective barrier against infection until it gets injured. If you get a cut, however, bacteria can enter your body. Your immune system reacts very quickly-- you can tell by the redness and swelling. That’s why it’s important to wash cuts and scrapes with water and soap; you want to wash away the pathogens before they enter the body.

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 FirstGov  NASA
Editor: Carol Elland
NASA Official: B J Navarro
Last Updated: September 2006
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