Q. I seem to be getting sick a lot lately and I'm worried that my immune system isn't working right. Could that be a reason?

A diminished immune system could be the cause of your problems. Go to your doctor for a checkup and diagnosis.

The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by organisms such as bacteria, parasites, and fungi that can cause infections.

The cells that are part of this defense system are white blood cells, or leukocytes. Foreign substances that invade the body are called antigens.

No two individuals have the same immune system. Some people seem to be dressed in a suit of armor against infections while others get floored whenever there are bugs about.

When it comes to germs, getting older has advantages and disadvantages.

As we age, our immune systems develop defenses against antigens. We acquire antibodies to the germs we've defeated in the past. Because of this phenomenon, adults tend to get fewer colds than children.

Now for some of the bad news:

Ÿ The thymus, which is located behind the breastbone, is one of the organs of the immune system. The thymus is where immune cells white blood cells called T lymphocytes (T cells) mature. The thymus begins to shrink when we are young adults. By middle age it is only about 15 percent of its maximum size.

Ÿ Some T cells kill antigens directly. Others help coordinate other parts of the immune system. Although the number of T cells does not decrease with aging, T-cell function decreases. This causes parts of the immune system to weaken and increases the risk for becoming ill.

Ÿ Macrophages, which are white blood cells that ingest antigens, don't work as quickly as they used to. This slowdown may be one reason that cancer is more common among older people.

Ÿ There are fewer white blood cells capable of responding to new antigens. Thus, when older people encounter a new antigen, the body is less able to remember and defend against it.

Ÿ The amount of antibodies produced in response to an antigen is less in older people, and the antibodies are less able to attach to the antigen. These changes may partly explain why pneumonia, influenza, infectious endocarditis, and tetanus are more common among older people and cause death more often. These changes may also partly explain why vaccines are less effective in older people.

Ÿ 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. Among the autoimmune disorders are: lupus, rheumatoid arthritis, scleroderma and ankylosing spondylitis.

Ÿ Diabetes, which is also more common with increasing age, can also lead to decreased immunity.

There are immunizations that are important as we get older. Adult tetanus 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.

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