Aging changes in immunity

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Immune system structures

BACKGROUND

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.

EFFECT OF CHANGES

The immune system loses it's ability to fight off infections as you grow older. This increases your risk for getting 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.

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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.