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Your immune system is a collection of organs, special cells,
and substances that help protect you from some infections and diseases.
Immune system cells and the substances they make circulate through your
body to protect it from germs that cause infections. They also help
protect you in some ways from cancer.
It may help to think of your body as a castle. Think of
viruses, bacteria, and parasites as hostile, foreign armies that are
not normally found in your body. They try to invade your body to use
its resources to serve their own purposes, and they can hurt you in the
process. In fact, doctors often use the word foreign to describe
invading germs or other substances not normally present in the body.
The immune system is your body's defense force. It helps keep
invading germs out, or helps kill them if they do get into your body.
The immune response
Any substance that raises an alarm in the body, causing the
immune system to react to and attack it is called an antigen. This
immune response can lead to destruction of both the antigens and
anything they are attached to, such as germs or cancer cells.
Germs such as viruses, bacteria, and parasites have substances
on their outer surfaces, such as certain proteins, that are not
normally found in the human body. The immune system sees these foreign
substances as antigens. Cancer cells are also different from normal
cells in the body. They often have some unusual substances on their
outer surfaces that can act as antigens.
But the immune system is much better at recognizing and
attacking germs than it is cancer cells. Germs are very different from
normal human cells and are seen as truly foreign. But cancer cells and
normal cells can be very much alike, and any differences are less clear
cut. Because of this the immune system may not always recognize cancer
cells as foreign. Cancer cells are less like soldiers of an invading
army and more like traitors within the ranks of the human cell
population. This may be why cancers are often able to grow despite the
presence of a healthy, working immune system.
Go back
to Immunotherapy.
Last Medical Review: 08/25/2009
Last Revised: 08/25/2009
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