What the immune system does
Your immune system is a collection of organs, special cells, and substances that help protect you from infections and some other diseases. Immune system cells and the substances they make travel through your body to protect it from germs that cause infections. They also help protect you from cancer in some ways.
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 found 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 system basically works by keeping track of all of the substances normally found in the body. Any new substance in the body that the immune system does not recognize raises an alarm, causing the immune system to attack it. Substances that cause an immune system response are called antigens. The immune response can lead to destruction of anything containing the antigen, 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 unusual substances on their outer surfaces that can act as antigens.
But the immune system is much better at recognizing and attacking germs than cancer cells. Germs are very different from normal human cells and are often easily seen as foreign, but cancer cells and normal cells have fewer clear differences. 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.
Clearly the immune system’s normal ability to fight cancer is limited, because many people with healthy immune systems still develop cancer. The immune system may not see the cancer cells as foreign because the cancer cells (and their antigens) are not different enough from those of normal cells. Sometimes the immune system recognizes the cancer cells, but the response may not be strong enough to destroy the cancer. Cancer cells themselves may also give off substances that keep the immune system in check.
To overcome this, researchers have designed ways to help the immune system recognize cancer cells and strengthen its response so that it will destroy them.
Last Medical Review: 05/09/2012
Last Revised: 02/22/2013