Aging and the immune system.

AGING & THE IMMUNE SYSTEM 

Clyde is celebrating his sixty-third birthday in Sutter Memorial Hospital - surrounded by monitors, tubes, and strangers in sterile white clothes. Trudy, his wife, watches helplessly as the physicians try to stem the debilitating tide of pneumonia.

Throughout his life Clyde had always been the picture of robust health. He took great pride in the fact that he rarely suffered from colds or flu. After the October accident, however, his health began to deteriorate.

While pruning an orange tree in his backyard one afternoon, Clyde fell off the ladder and broke his ankle. Trudy rushed him to the emergency room, where the physician carefully reset the ankle, prescribed some pain medication, and sent him home to recuperate. The dull pain, however, made it impossible to sleep well. His appetite became so poor that he lost weight, energy, and his usual hearty humor.

A month ago Clyde caught a cold from a well-meaning visitor. Trudy gave her husband the usual care and medication, but nothing seemed to help. His condition worsened progressively; finally the doctor insisted that Clyde be hospitalized. Today, Clyde is struggling just to stay alive.

There are more than 25 million Americans aged 65 or older who are at risk for immune-related disorders and/or complications. Ailments such as pneumonia, tuberculosis, and shingles are significantly more common in the elderly, whose immune systems have been compromised. The elderly also suffer more frequently from "autoimmune" diseases such as lupus erythematosus or rheumatoid arthritis, where the body's defense network mistakenly attacks its own tissues, causing chronic inflammation and degeneration.

The story of the human defense system reads like a war novel:

The Body Under Siege.

The healthy human body is constantly on the alert. At any one time there are several million potential enemies in and around the body. These invaders are capable of reproducing themselves by the millions within a few short hours, using chemical warfare to destroy citizen cells and tissues, and stealing the body's own food supplies.

The foundation of our immune system is built around the several defense posts spread strategically throughout the body (see Figure 1). Our lymph nodes, operated by the B-cells, are major centers for the training and breeding of the different species of "attack dogs," called antibodies. We notice the nodes most when they become swollen during periods of infection.

Our defense system's headquarters is at the thymus, located between the lungs and just behind the upper part of the sternum. Here, "new recruits" from the bone marrow come to be instructed in T-cell (T is for thymus) combat. More important, this center is responsible for directing all of the body's combat operations, from enemy recognition and battle strategy to coordinating a cease-fire and retreat when the enemy has been defeated.

The attack begins the moment an invader (bacteria, virus, or foreign body) is encountered anywhere in the body. As soon as one of the body's cells is aggressed by a hostile invader it releases a distress signal that warns the immune system commanders (see Figure 2).

1. Immediately a few of the immune system's local macrophages respond to the distress signal and attack the invader, munching him to death - similar to "Pac-Men" of video game fame.

2. Next, the macrophage takes a piece of the invader's uniform (called the "antigen"). This uniform "scent" is delivered to the B-cell for use in the training of the "attack dogs" (antibodies). One sniff of the uniform (antigen) is enough. The dogs are off to track and kill the invader. Further, a group of sharp shooters known as the NK (natural killer) T-cells also receive this antigen "scent" to enable them to accurately identify the enemy.

3. Now a mad rush is on - more killer cells, attack dogs, and Pac-Men converge at the site of the invasion to launch an all-out assault on the enemy.

Unfortunately, this enthusiastic group of fighters doesn't know when to quit. If it were not for the T-suppressor cells, our immune system's lethal gang would cause great harm to its own cell population. Luckily, the T-suppressor cells know exactly when to put the "brakes" on. They call the cease-fire. Then, at last, the body is able to start a recovery process.

The Aging Factor.

The Thymus. The immune system's executive director, the thymus, is the organ that is most affected by age. At about the time of sexual maturity, the thymus starts to shrink in size. By age 20, the thymus has lost 75 percent of its size and function; by age 60, it is virtually gone. This thymic shrinkage results in a significant change in the number and activity of "trained" T-cell combatants.

The T-Cells. A normal population of mature T-cells - composed of T-helper, T-suppressor, and natural killer cells - must keep a certain numerical strenght and proportion between themselves in order to be effective combatants. A healthy immune system usually has about two helper cells for every suppressor cell (a ratio of 2 to 1).

An elderly individual, however, has a proportionate increase in T-suppressor cells that approaches a 1 to 1 ratio (similar to that of AIDS patients suffering from an immune deficiency syndrome). The suppressor cells, now dominant, prematurely "turn off' the body's battlefield managers, the T-helper cells, allowing the enemy troops to recover and attack again.

The "Attack Dog Trainers." The actual number of B-lymphocytes are not significantly affected by aging, but something seems to go wrong with cell regulation. The unregulated B-cell produces autoantibodies - a bunch of attack dogs that can't tell the difference between the scent of enemy cells and citizen cells. Such autoantibodies may even combine with autoantigens to create a monster structure called the "immune complex." It has been found that nearly one half of healthy persons over age 65 have high levels of circulating immune complexes. These monster structures play an important role in the disease process called arteriosclerosis ("hardening of the arteries").

Building and Maintaining the Immune

System.

Nutrition. Poor eating patterns can lead to nutrient deficiencies, which in turn contribute to a depressed immune system. Vitamins A, B6, E, and C, found in many grains, legumes, and green and yellow fruits and vegetables, all play important roles in maintaining the vitality of the immune response.

Calorie intake is another area that is attracting much attention from the scientific community. Moderate or severe protein-calorie restriction has been associated with gross deficiencies in antibody production and a defective inflammatory expression. However, when adequate levels of vitamins and minerals were added, the immune function did not suffer, and in some cases actually increased.

Drs. Good and Lorenz from the University of South Florida have spent more than 15 years investigating nutrition's influence on autoimmune disease and other diseases associated with aging in mice. The mice were genetically predisposed to die early from several types of cancer and autoimmune disease. However, when carefully designed low-calorie diets were given to these mice, the researchers were amazed to discover that the mice lived much longer than expected, with significantly less disease.

They conclude that restriction of total calorie intake - undernutrition (as opposed to malnutrition) - has a dramatic positive effect on immune function as well as on longevity.

Exercise. Moderate exercise may increase the body's ability to kill enemy organisms. More research is needed to confirm these preliminary findings. On the other hand, several studies seem to suggest that intense training increases susceptibility to illness and produces long-term damaging effects on the immune system. Dr. David Nieman, professor of health science at Loma Linda University, analyzed "infectious episode" data collected from 1,828 Los Angeles marathoners. He concluded that the athletes who did heavy training were at increased risk for infection. Specifically, the researchers found a significant depression in natural killer cell activity immediately following the marathon event.

Much has yet to be learned about exercise's contribution to disease resistance. "In the meantime, regular aerobic activity, with moderate exertion, is still the best bet for a healthier heart and immune system," Dr. Nieman advises.

Stress. When one suffers from psychological stress, the body produces a substance called cortisol. This hormone is known to be a powerful immunosuppressant, which, if sustained by chronic stress, is capable of destroying the lymphoid tissues of the thymus and lymph nodes. In consequence, the immune system loses its ability to recognize and destroy any invading organism.

In 1986 the American Journal of Epidemiology reported a study done by Drs. Graham, Douglas, and Ryan, who found that individuals who were under chronic psychological stress were likely to suffer from cold or flu symptoms for twice as many days as persons with low stress. Apparently, stress suppresses both natural killer activity and the ability to rapidly respond to the distress signals from tissues under attack.

By far, the best way to avoid the harmful effects of stress is to learn proper stress management techniques. Laughter, thinking positively, and contemplating God's blessings have each demonstrated great promise in reducing stress levels.

The Bottom Line.

It is an inevitable part of living that one must succumb to the process of aging. Nevertheless, most of the body's functions are incredibly resilient, determined to remain well and operative, if only given proper care.

The body's continous battle against disease-causing organisms requires our faithful attention to appropriate nutrition, exercise, and stress management. Medical doctors, health psychologists, doctors of health science (D.H.Sc.), nutritionists (R.D.) and many other qualified professionals can offer a health-concious individual the kind of personal and comprehensive lifestyle program that will promote a hardy immune system and a longer, healthier life.