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Immune system structures
Immune system structures




The thymus, one of the organs of the immune system, is the site where certain immune cells called T lymphocytes (T cells) mature. The thymus begins to shrink (atrophy) after adolescence. By middle age it is only about 15% of its maximum size.

Some of the T cells directly kill foreign particles. Others help coordinate other parts of the immune system, which are specialized to attack different types of infections.

Although the number of T cells does not decrease with aging, T-cell function decreases. This causes parts of the immune system to weaken.


The immune system loses it's ability to fight off infections as you grow older. This increases your risk for geting sick, and may make immunizations less effective. Flu shots or other immunizations may not work as well, and protection may not last as long as expected. The immune system's ability to detect and correct cell defects also declines, which results in an increase in cancers associated with aging.

Later in life, the immune system also seems to become less tolerant of the body's own cells. Sometimes an autoimmune disorder develops -- normal tissue is mistaken for non-self tissue, and immune cells attack certain organs or tissues.

Other things also increase the risk of infections. Sensation changes, gait changes , changes in the skin structure, and other "normal aging changes" increase the risk of injury in which bacteria can enter broken skin. Illness or surgery can further weaken the immune system, making the body more susceptible to subsequent infections. Diabetes, which is also more common with increasing age, can also lead to decreased immunity.

Aging also affects inflammation and wound healing. Inflammation is an immune response -- when the immune system thinks there is trouble, it sends more cells to the site of the problem. This causes swelling, pain, redness, warmth, and irritation. Inflammation is often a sign of infection, but it may also occur as part of an autoimmune attack.

Many older people heal more slowly. This may be directly related to changes in the immune system, or it may be a result of other problems such as diabetes or arteriosclerosis, which leads to decreased blood flow to some parts of the body such as the lower legs.

Also, many older people take anti-inflammatory medications (to control conditions such as arthritis ), which are known to slow wound healing.


  • Increased infection risk
  • Decreased ability to fight diseases
  • Slowed wound healing
  • Autoimmune disorders
  • Cancer


Just as routine immunizations are important to prevent illness in children, a few routine immunizations are important as we get older. Adult tetanus (Td) immunizations should be given every 10 years (a booster may be given sooner if there is a dirty wound).

Your health care provider may recommend other immunizations, including Pneumovax (to prevent pneumonia or its complications), flu vaccine , hepatitis immunization, or others. These optional immunizations are not necessary for ALL older people, but are appropriate for some.

Keeping generally healthy also helps. Maintaining good health involves:

  • Exercise
  • A well-balanced diet
  • No smoking
  • Limited alcohol use -- moderate drinking seems to have some health benefits, but excessive drinking can cause serious damage
  • Safety measures to avoid falls and other injuries


Review Date: 10/27/2008
Reviewed By: Michael Langan, M.D. Department of Geriatrics, Massachusetts General Hospital, Boston, MA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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789 Central Avenue, Dover, NH 03820
Phone: (603) 742-5252
Toll free: 1 (877) 201-7100