Our immune system is one of the first to be compromised by normal aging. The master gland of the immune system, our thymus, is a pink, flat, two-lobed gland located under the sternum. It weighs about 1.5 ounces when we are about 11 years old, but begins to shrink quickly with the onset of puberty. When we turn 40, it is only 10 to 15 per cent of the size that it was at age 11. One obvious result of this shrinkage is a decline in the production of hormones that organize and direct the B-cells and T-cells. The thymus also becomes less effective in converting immature white blood cells into fully functioning T-cells, and as those all important T-cells are less able to do their job, the whole immune army is thrown out of step. Because the thymus deteriorates early, the power of the immune system peaks in adolescence and goes downhill after that stage.
The deterioration of the system is more qualitative than quantitative. The number of white blood cells we possess at age 80 is about the same as when we were 20 years old, but these senile white blood cells are less effective in receiving and transmitting commands. They may also experience difficulty in reaching their proper destination.
Now the entire immune system is compromised. B-cells and T-cells no longer coordinate their actions to destroy and remove invading organisms. This results in older people becoming more susceptible to infection. An increase in the rates of influenza, pneumonia, tuberculosis and other diseases in the elderly prove this point.
Cancer incidences are of particular concern to us today. Scientists assume that our body produces cancer cells at a fairly consistent rate throughout life. Younger immune systems (mostly through T-cells) are more efficient in identifying and killing these malignant cells before they multiply and spread throughout the body. Older immune systems simply allow more of these cancer cells to 'get by the goalie'.
The one antibody that does seem to strengthen as we age is an autoimmune type. This is most undesirable, since its presence causes our body to literally attack itself. B-cells begin producing auto-antibodies targeted to the lining of our blood vessels, nerves, and other normal cells in response to the errors made by our aging immune system. Our own cells now become labeled as the enemy by the B-cells. Auto-antibodies can be found in the blood of nearly every older person, and researchers suspect they play a part in conditions ranging from heart disease and arthritis to neurological ailments.
The T-cells actually cause this collapse of the normally highly efficient immune system. By loosening the T-cells' control over the B-cells, the B-cells are allowed to produce increasing quantities of antibodies. Researchers have found that people with higher concentrations of auto-antibodies in their blood tend to run increased risks of cancer and heart disease, and have a generally shorter lifespans.
We really don't know exactly why the T-cells degenerate in function or why the thymus shrinks. It is probably due to a decrease in the adrenal androgen DHEA. The following table lists diseases that result from the production of auto-antibodies:
Diseases Part of body attacked
Rheumatoid arthritis Joint linings
Graves' disease Thyroid gland
Multiple sclerosis Nerve fibres
Diabetes Pancreas cells
The combination of T-cells and B-cells elevates antibody levels, and the shrinking thymus adds up to a weaker immune system with advancing years. Still our immune system serves us quite well throughout our life. Phagocytes do not appear to lose any of their power with age. Although our ability to fight off a new infection declines with age, our immune memory response remains unimpaired throughout life. That allows our body to continue to fight off most infections, especially those which we have been exposed to before.
Middle age and beyond does not signal the likelihood of cancer or a significant increase in other infections and diseases. We can keep this beautifully designed system functioning the way nature has intended and eliminate our vulnerability to 'diseases of aging'. It is possible to significantly increase our longevity, while maintaining a high quality of life.