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E-book Understanding the Immune System : How it Works
The immune system is a network of cells, tissues*, and organs that work together to defend the body against attacks by “foreign” invaders. These are primarily microbes (germs)—tiny, infection-causing
organisms such as bacteria, viruses, parasites, and fungi. Because the human body provides an ideal environment for many microbes, they try to break in. It is the immune system’s job to keep them out
or, failing that, to seek out and destroy them. When the immune system hits the wrong target or is crippled, however, it can unleash a torrent of diseases, including allergy, arthritis, or AIDS. The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can produce secretions and cells to match up with and wipe out each one of them.
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