This Month's HIV/AIDS Facts

These facts contain commonly accepted public health information about the prevention and transmission of HIV and AIDS. If this is not the information that you are seeking, please use the Back button on your browser to visit another section of our site. Thank you.

Question: What is the immune system? Why is the immune system important? What are antibodies?

Basic Answer: The immune system is a collection of cells and substances, including white blood cells, T cells and antibodies, that act as the body’s defense against germs and other things that make people sick. Antibodies are substances that form in the blood when germs enter the body. Antibodies usually defend against illnesses and infections, although HIV antibodies do not always protect against HIV infection.

Detailed Answer: The immune system is a collection of cells and substances, including white blood cells, T cells and antibodies, that act as the body’s defense against germs and bacteria. When the system works as it should, white blood cells circulate in the body and attack any organisms that should not be there. Some of these blood cells attack germs directly, by engulfing them; other cells make antibodies in response to invading germs. Antibodies usually defend against illnesses and infections, although this is not usually the case with HIV antibodies. Because HIV can easily change parts of its genetic make-up as it replicates, it can escape attack by the body’s defenses. When the immune system is damaged, it is less effective at protecting the body against illnesses and infections.

Scientists are studying how the immune systems of some people with HIV can continue to mount an effective defense against the virus for many years. Individuals in this category have been called “long-term nonprogressors.” They have healthy immune systems, show no signs of AIDS-related symptoms and their T cell count remains stable over a period of many years even without any treatment.

SOURCES:

• National Institutes of Health. The Immune System--How It Works. NIH Publication 92-3229. January 1999.
• DeVita, V., Jr., et al., eds. AIDS: Etiology, Diagnosis, Treatment and Prevention, 4th ed. 1997.

For current statistics, contact the CDC National AIDS Hotline (800/342-AIDS), Spanish (800/344-7432), TTY/TDD (800/243-7889); the CDC Voice and Fax Information System (888/232-3228); the CDC National Prevention Information Network (800/458-5231) or its Web site at www.cdcnpin.org; or the CDC HIV/AIDS Web site at www.cdc.gov/hiv/dhap.htm.