What do rheumatoid arthritis (RA), type 1 diabetes, Graves' disease, and multiple sclerosis have in common? One affects joints, another blood sugar. One puts the thyroid into “overdrive.” And the last condition affects the brain and spinal cord. Although the diseases seem pretty different, there is one common denominator. They are all believed to be autoimmune diseases.
RA is one of about 80 different types of autoimmune diseases. After cancer and heart disease, autoimmune diseases are the most common type of disease in the U.S., affecting 50 million Americans. Women make up nearly eight out of every 10 people with an autoimmune disease.
In every issue of WebMD the Magazine, we ask our experts to answer readers' questions about a wide range of topics. In our May 2011 issue, a reader with rheumatoid arthritis asked WebMD's rheumatology expert, Scott Zashin, MD, why her husband doesn't help her more.
What is the common link between autoimmune diseases? And how does autoimmunity lead to rheumatoid arthritis? Here’s what you need to know.
What Is the Immune System?
To understand autoimmune diseases such as RA, it helps to know how the immune system normally works. Its most important job is protecting your body against foreign “invaders,” such as bacteria and viruses. White blood cells are the agents of the immune system. The immune system works in two main ways. It either directly attacks foreign invaders or it produces proteins called antibodies that attack the intruders.
“Normally, the choreography of this interaction between the white blood cells works very well,” says John A. Peyman, PhD, program officer in the clinical immunology branch of the National Institute of Allergy and Infectious Diseases (NIAID).
He tells WebMD that the body can tell what is a threat and what isn’t. When you have a cut on your finger, for example, you may end up with a small infection caused by germs that enter the wound. This prompts a type of immune response known as inflammation -- often marked by redness, swelling, heat, and pain. Then the immune system’s white blood cells heal the wound and remove the infection.
What Are Autoimmune Diseases?
With an autoimmune disease like RA, however, something goes awry. The white blood cells overreact to stimuli inside the body. Instead of protecting the body from infection or disease as it normally does, the immune system attacks and destroys the body’s healthy tissue. It does this by producing antibodies against the body’s tissue. This is called autoimmunity.
When the disease affects many organs, as in lupus, it’s called a systemic autoimmune disease. If it affects a single organ or type of tissue, such as in type 1 diabetes, it’s known as a localized autoimmune disease. Different autoimmune diseases often cluster in families and may affect almost any organ in the body. When they do, they may cause abnormal growth or changes in function.
There are some similarities to allergies in the way the body reacts negatively with an autoimmune disease. The difference is that with allergies, the body’s overreaction and response is to external factors such as dust or dander. With an autoimmune disease, the body is responding to itself.