11.58: Autoimmune Disease

Does pollen make you sneeze?

If so, you are not alone. It is one of the most common allergies. The runny nose and sneezing associated with allergies results from the immune system working improperly.

Diseases of the Immune System

The immune system usually protects you from pathogens and other causes of disease. When the immune system is working properly, it keeps you from getting sick. But the immune system is like any other system of the body. It can break down or develop diseases.

AIDS is an infectious disease of the immune system caused by a virus. Some diseases of the immune system are noninfectious. They include autoimmune diseases and allergies.

Autoimmune Diseases

Does it make sense for an immune system to attack the cells it is meant to protect? No, but an immune system that does not function properly will attack its own cells. An autoimmune disease is a disease in which the immune system attacks the body’s own cells.

One example is type 1 diabetes. In this disease, the immune system attacks cells of the pancreas. Other examples are multiple sclerosis and rheumatoid arthritis. In multiple sclerosis, the immune system attacks nerve cells. This causes weakness and pain. In rheumatoid arthritis, the immune system attacks the cells of joints. This causes joint damage and pain.

Autoimmune diseases cannot be cured. But they can be helped with medicines that weaken the immune system’s attack on normal cells. Other autoimmune diseases include celiac disease (damages to the small intestine), inflammatory bowel disease (damage to the digestive tract), psoriasis (damage to the skin), and lupus (damage to the joints, skin, kidneys, heart, and lungs).

Allergies

An allergy occurs when the immune system attacks a harmless substance that enters the body from the outside. A substance that causes an allergy is called an allergen. It is the immune system, not the allergen, that causes the symptoms of an allergy.

Did you ever hear of hay fever? It’s not really a fever at all. It’s an allergy to plant pollens. People with this type of allergy have symptoms such as watery eyes, sneezing, and a runny nose. A common cause of hay fever is the pollen of ragweed. Many people are also allergic to poison ivy (Figure below). Skin contact with poison ivy leads to an itchy rash in people who are allergic to the plant.

Figure \(\PageIndex{1}\): Ragweed is a common roadside weed found throughout the United States. Many people are allergic to its pollen.

Figure \(\PageIndex{2}\): Poison ivy plants are wild vines with leaves in groups of three. They grow in wooded areas in most of the United States. Contact with poison ivy may cause a rash in a person allergic to the plant.

Some people are allergic to certain foods. Nuts and shellfish are common causes of food allergies. Other common causes of allergies include:

• Drugs, such as penicillin.
• Mold.
• Dust.
• The dead skin cells of dogs and cats, called dander.
• Stings of wasps and bees.

Most allergies can be treated with medicines. Medicines used to treat allergies include antihistamines and corticosteroids. These medicines help control the immune system when it attacks an allergen. Sometimes, allergies cause severe symptoms, a condition known as anaphylaxis‎. For example, they may cause the throat to swell so it is hard to breathe. Severe allergies may be life threatening. They require emergency medical care.

Summary

• Autoimmune diseases occur when the immune system attacks normal body cells.
• Allergies occur when the immune system attacks harmless substances that enter the body from the outside.

Explore More

Use the resources below to answer the questions that follow.

Explore More I

• Malfunction of the Immune System at http://www.youtube.com/watch?v=YO_ph9wvFkI (2:06)

1. How does your immune system respond when you have allergies?
2. What happens when a person has Rheumatoid Arthritis? What sort of disease is this?

Explore More II

• Problems of the Immune System at http://kidshealth.org/parent/general/body_basics/immune.html

1. List the four categories of immune system disorders.
2. What is an immunodeficiency?
3. Describe SCID.
4. What type of immune disorder is lupus?
5. What are two cancers of the immune system?

Review

1. What is an autoimmune disease?
2. What causes rheumatoid arthritis?
3. What causes an allergy?