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Autoimmune Diseases

Describes diseases in which the immune system attacks the body’s own cells.

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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. These diseases cannot be cured. But they can be helped with medicines that weaken the immune system’s attack on normal cells.


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 (Figure below).

Ragweed is a common roadside weed found throughout the United States. Many people are allergic to its pollen.

Many people are allergic to poison ivy (Figure below). Skin contact with poison ivy leads to an itchy rash in people who are allergic to the plant.

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.

As you have read, 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. 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.


  • allergy: Over-sensitivity of the immune system when it attacks a harmless substance.
  • autoimmune disease: Disease in which the immune system attacks the body’s own cells.
  • multiple sclerosis: Disease in which the immune system attacks nerve cells, resulting in weakness and pain.
  • rheumatoid arthritis: Disease in which the immune system attacks the cells of joints, causing joint damage and pain.
  • type 1 diabetes: Disease in which the immune system attacks normal cells of the pancreas, preventing the production of insulin.


  • 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.


Use the resources below to answer the questions that follow.

  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?
  1. How does your immune system typically work?
  2. What role does inflammation play in the immune system. Is inflammation a good thing? Why or why not?
  3. What are the three types of immune system disorders? How do these types differ?
  4. What is hypersensitivity? What is type 1 hypersensitivity more commonly know as?
  5. How do the different types of hypersensitivity differ from each other?


  1. What causes rheumatoid arthritis?
  2. What causes an allergy?

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