Aging and the Immune System

As the human body enters its senior years, its ability to fight off infection and other health problems diminishes significantly. The immune system, which is responsible for fighting infection, simply does not function as efficiently in older adults as in younger people.

The body's innate response to infection -- mounting a fever to kill cells causing illness, for example -- is not always automatic in elderly people. In fact, more than 20% of adults over age 65 who have serious bacterial infections do not have fevers. The body at this age probably still has the ability to generate fevers and other immunity weapons, but the central nervous system is simply less sensitive to immune signals and doesn't react as quickly or efficiently to infection.

Lymphocytes, which are cells produced in the lymph glands, are essential to the body's production of antibodies used to fight infection. The overall number of lymphocytes does not change greatly in old age, but the configuration of lymphocytes and their reaction to infection does.

Elderly adults are less capable of producing lymphocytes to combat challenges to the immune system. The infection-fighting cells that are produced are less vigorous and less effective than those found in younger adults. When antibodies are produced, the duration of their response is shorter in older adults and fewer cells are produced than in younger adults. The immune system of younger adults -- including lymphocytes and other types of cells -- typically reacts more strongly and more rapidly to infection than does an older adult's.

In addition, elderly adults, particularly after age 70, are more likely to produce autoantibodies, which attack parts of the body itself instead of infections. Autoantibodies are factors in causing rheumatoid arthritis and atherosclerosis (hardening of the arteries).

Improving the Immune System Response

As the human body grows old, so does its organs. The organs are less efficient than when the body is younger. The thymus, for example, secretes important hormones, particularly during puberty. In elderly people, however, it is largely dormant. But when lymphocytes of older adults are exposed to thymic hormones, the immune system is enhanced at least temporarily. The secretion of hormones, including growth hormone and melatonin, decline in old age and may be related to a compromised immune system.

Certain prostaglandins, hormone-like acids that affect important body processes such as body temperature and metabolism, may increase in old age and inhibit important immune cells from doing their jobs. Older adults may also be more sensitive to the action of prostaglandins than younger adults, which could be a major cause of immune deficiency in elderly people. Prostaglandins are produced by most tissues in the body, but the immune system responds better in older adults when prostaglandin production is suppressed.

Nutrition also plays a factor in a healthy immune system. In both healthy and nutritionally deficient older adults, vitamin and dietary supplements have been found to enhance the response of the immune system, resulting in fewer days of infectious illnesses.

Older adults often experience loss and stress, and suppressed immunity has been associated with bereavement, depression and poor social support. Maintaining an active social life and receiving treatment for depression could boost the older adult's immune system.

It has not been proven that a less effective immune system necessarily means more infections or a shorter life. However, in general, older adults experience more infections and a greater severity of infections than younger adults. In addition, older adults display a decreased response to vaccines, including that for streptococcal pneumonia, that should protect them from infections. This is particularly important where influenza (the flu) is concerned because the elderly account for more than 80% of the deaths related to epidemics. Tetanus is another concern, since more than 70% of people over age 70 never received the necessary tetanus vaccinations.

While vaccines do not work as well in the immune system of older adults, vaccinations for diseases such as influenza, pneumonia, hepatitis B, tuberculosis, diphtheria and tetanus have been found to reduce mortality in the elderly and are still worthwhile.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.