In some individuals, the immune system can become a problem, either by not working adequately or working too aggressively. Conditions of this nature are called either immune-mediated (the immune system allows damage to take place without intervening) or autoimmune (the immune system mistakenly attacks the body's own tissues). Some conditions that result from the immune system behaving incorrectly include:

• Allergies. Reaction caused when the immune system “mistakes” a non–threatening substance as dangerous. The body reacts to remove the threat, causing symptoms such as sneezing, runny nose, coughing, itching, nausea, diarrhea or shortness of breath.
  
  
• Allergic asthma. Condition where allergens (e.g., pollen, dander, mold) trigger an asthma attack. When inhaled, the allergens cause the airway passages in the lungs to become inflamed, resulting in symptoms such as coughing, wheezing and shortness of breath.
  
  
• Type 1 diabetes. Condition where insulin–producing cells in the pancreas are mistaken as dangerous by the immune system, making it difficult for the body to convert food into energy.
  
  
• Rheumatoid arthritis. Condition in which the immune system incorrectly causes an inflammation of the membrane lining the joints of the hands and feet, causing pain and stiffness in the joints.
  
  
• Multiple sclerosis. Condition in which the immune system damages the nerve tissues in the central nervous system.
  
  
• Inflammatory bowel diseases. Condition in which the immune system attacks the intestines. This includes Crohn’s disease and ulcerative colitis.
  
  
• Lupus erythematosus. Condition in which the immune system may attack and damage the kidney, brain or lungs.
  
  
• Psoriasis. Condition in which the immune system sends signals that cause skin growth to speed up, resulting in the itchy, flaky buildup of skin.
  
  
• Scleroderma. Condition in which the immune system causes the skin and blood vessels to thicken, resulting in a loss of movement and shortness of breath.
  
  
• Autoimmune thyroid diseases. Conditions in which the immune system damages or stimulates the tissues of the thyroid. Conditions of this type include Hashimoto’s thyroiditis and Grave’s disease.
  
  
• Sjogren’s syndrome. Condition in which immune system reacts against some of the bodies own tissues, damaging the glands that produce tears and saliva.
  
  
• HIV (human immunodeficiency virus). Condition whereby the immune system becomes depressed and is unable to fight infections.

Even a properly functioning immune system may present problems for some people – such as those undergoing organ or tissue transplants. Trying to protect the body, the immune system attacks transplanted organs or body tissue as foreign invaders. This can have serious consequences for the donor recipient.  For this reason, transplant patients are required to take medications (immunosuppressants) to hold back the immune system from attacking.