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 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. Germs like viruses, bacteria, and parasites are like hostile, foreign armies that are not normally found in your body. They try to invade your body to use its resources, and they can hurt you in the process. Your immune system is your body’s defense force. It helps keep invading germs out, or kills them if they do get into your body.
The immune system keeps track of all of the substances normally found in the body. Any new substance in the body that the immune system doesn’t recognize raises an alarm, causing the immune system to attack it. Substances that cause an immune response are called antigens. The immune response can destroy anything containing the antigen, such as germs or cancer cells.
Germs 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 and attacks them.
Cancer cells are also different from normal cells in the body. They sometimes have unusual substances on their outer surfaces that can act as antigens. But germs are very different from normal human cells and are often easily seen as foreign, whereas cancer cells and normal cells have fewer clear differences. Because of this, the immune system doesn’t 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 there are limits on the immune system’s ability to fight cancer on its own, because many people with healthy immune systems still develop cancer. Sometimes the immune system doesn’t see the cancer cells as foreign because the cells are not different enough from normal cells. Sometimes the immune system recognizes the cancer cells, but the response might not be strong enough to destroy the cancer. Cancer cells themselves can also give off substances that keep the immune system in check.
To overcome this, researchers have found ways to help the immune system recognize cancer cells and strengthen its response so that it will destroy them.
Last Medical Review: 03/19/2014
Last Revised: 09/05/2014