What Are Immune System Disorders?

Immune system disorders cause abnormally low activity or overactivity of the immune system. In cases of immune system overactivity, the body attacks and damages its own tissues (autoimmune diseases). Immune deficiency diseases decrease the body's ability to fight invaders, causing vulnerability to infections.

Allergies and Asthma

Allergies result from the immune system's overreaction to a non-threatening foreign substance. Foods and inhaled particles like pollen and pet dander are the most common allergens (substances causing allergic reactions). When the immune system senses an allergen, it stimulates the release of chemicals such as histamine.

Symptoms of the resulting allergic reaction can include breathing problems, eye irritation, rash, nasal congestion, or nausea and vomiting. Antihistamine medications can reduce symptoms, but avoiding allergen exposure is the best preventive treatment for allergies.

Asthma is a condition in which the immune system becomes overactive in the airways (bronchi) in the lungs. People with asthma suffer periodic episodes of constriction of their airways (bronchospasm), making it harder to breathe. Most people with asthma also have ongoing inflammation in their airways. Asthma treatment sometimes includes a daily inhaled corticosteroid, which reduces immune system overactivity and inflammation.

Autoimmune Diseases

In response to an unknown trigger, the immune system may begin producing antibodies that instead of fighting infections, attack the body's own tissues. Treatment for autoimmune diseases generally focuses on reducing immune system activity. Examples of autoimmune diseases include:

Rheumatoid arthritis. The immune system produces antibodies that attach to the linings of joints. Immune system cells then attack the joints, causing inflammation, swelling, and pain. If untreated, rheumatoid arthritis causes gradually causes permanent joint damage. Treatments for rheumatoid arthritis can include various oral or injectable medications that reduce immune system overactivity.

Systemic lupus erythematosus (lupus). People with lupus develop autoimmune antibodies that can attach to tissues throughout the body. The joints, lungs, blood cells, nerves, and kidneys are commonly affected in lupus. Treatment often requires daily oral prednisone, a steroid that reduces immune system function.

Inflammatory bowel disease (IBD). The immune system attacks the lining of the intestines, causing episodes of diarrhea, rectal bleeding, urgent bowel movements, abdominal pain, fever, and weight loss. Ulcerative colitis and Crohn's disease are the two major forms of IBD. Oral and injected immune-suppressing medicines can treat IBD.

Multiple sclerosis (MS). The immune system attacks nerve cells, causing symptoms that can include pain, blindness, weakness, poor coordination, and muscle spasms. Various medicines that suppress the immune system can be used to treat multiple sclerosis.

Type 1 diabetes mellitus. Immune system antibodies attack and destroy insulin-producing cells in the pancreas. By young adulthood, people with type 1 diabetes require insulin injections to survive.

Guillain-Barre syndrome.  The immune system attacks the nerves controlling muscles in the legs and sometimes the arms and upper body. Weakness results, which can sometimes be severe. Filtering the blood with a procedure called plasmapheresis is the main treatment for Guillain-Barre syndrome.