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What do the white blood cells do?
Many mature white blood cells are highly specialized. The
so-called T lymphocytes (T stands for thymus-derived) have various
functions, among them switching on various aspects of the immune
response, and then (equally important) switching them off. Another
lymphocyte, the B cell, manufactures antibodies. A larger kind of
white cell, the scavenger called the phagocyte (most notably the
macrophage), eats up all sorts of debris in tissue and the
bloodstream, and alerts certain T cells to the presence of
antigens.
In addition, there are killer, suppressor, and helper T cells.
Killer T cells, stimulated by helper T cells, zero in on cells
infected by antigens, or turn against the body's own cells when,
as in the case of cancer, they begin to proliferate abnormally.
Another class of lymphocyte killer cell is called "natural"
because, unlike T and B cells, it doesn't need to recognize a
specific antigen. Most healthy cells are of no interest to natural
killer cells, but cancer cells and cells invaded by viruses may be
vulnerable to their search-and-destroy missions.
What makes a person immune to
various diseases?
Thanks to the lymphocytes, the immune system possesses a memory,
or a sense of history. The lymphocytes manufacture antibodies
(proteins circulating in the blood) that attack intruders. Once
you have produced antibodies to a certain microbe—a specific flu
virus, for example—that particular virus cannot make you sick
again, because you have cells that immediately recognize it and
produce the antibodies that destroy it. The immunity may last for
years, sometimes for life. This is "acquired immunity."
 Science has also developed vaccines. It all began in the late
eighteenth century, when the English physician Edward Jenner
observed that people who caught a mild disease called cowpox never
got smallpox, which is related to it. Using a boy who had not had
either disease, Jenner tried inoculation: he scraped the child's
skin and applied secretions from cowpox sores, and the boy got
cowpox. When Jenner later inoculated him with smallpox matter, the
boy did not develop smallpox. (Such human experimentation would
land Dr. Jenner in court today.)
Creating immunity by injecting healthy people with dead or altered
disease-causing microbes has prevented millions of deaths from
measles, polio, diphtheria, flu, smallpox, tetanus, yellow fever,
and many other diseases. Vaccines truly are immune-system
boosters.
Does loss of sleep depress
immunity?
It can. But losing sleep for a few nights won't necessarily make
you ill. Many things boost or depress immunity temporarily. The
number of immune cells rises and falls naturally in healthy
people.
What foods boost immunity?
An adequate diet helps maintain immunity and keeps you healthy.
The immune system needs such nutrients as protein, fatty acids,
vitamins, and minerals. Severely malnourished people are
particularly vulnerable to immune dysfunction, and they get sick
more easily than other people and stay sick longer. What most
people want to know, though, is whether one specific food or kind
of food will boost immunity in otherwise healthy people on an
adequate diet. The answer is generally no though specific vitamins
have been shown to have a positive impact.
What supplements boost it?
Though severe malnutrition is rare in western countries some
groups, particularly the elderly, may be deficient in such
nutrients
as vitamin C, certain B vitamins, and
zinc. Studies suggest that raising nutrient intakes to adequate
levels can enhance immunity, and there is some evidence that
elderly people stay healthier if they take a multivitamins and
minerals.
Zinc found in meat and grains, is ideal for boosting the
immune-system when taken as a supplement. While some studies show
that zinc supplements can boost immunity and promote wound-healing
high doses can actually suppress the immune response.
A diet low in beta carotene can depress immunity, and therefore
supplementation would be helpful. Among the agents that have been
shown to stimulate immunity in experiments is the bacteria in
yogurt, but it's far from certain that consuming yogurt (with or
live cultures) will promote resistance to disease.
What about vitamin C?
This vitamin is necessary to good health and no doubt to immune
function. But numerous studies have shown that vitamin C
supplements have minimal or no effect on the immune response,
unless you are deficient in C or in a state of disease such as
when you have a cold.
Does exercise boost immunity?
Some research shows that sedentary people don't have as vigorous
an immune system as those who exercise. Moderate exercise (for
example, a moderate walking program undertaken by previously
sedentary people) seems to improve immune function. But there is
also evidence that overdoing exercise may depress the immune
system: high-intensity or prolonged endurance exercise steps up
the output of two so-called stress hormones, adrenaline and
cortisol, both of which can depress various components of the
immune system.
Olympians and other highly trained athletes often report that
after intense competition and training they are more susceptible
to colds. Yet such news should not deter athletes from competing
or exercisers from exercising.
The health benefits of exercise are clear. Regular aerobic
exercise is good for the heart. Weight-bearing exercise builds
bone and muscle. The idea that your immune cells might not show a
response to your exercise program should not deter you from
exercising or from beginning an exercise program if you are
sedentary.
Can emotions affect the
immune system?
States of mind surely affect health, and extreme emotional stress
may damage immunity and bring on illness. But research into the
link between mind and immunity is in its early stages and has
produced very little solid evidence so far and not much advice
about how to protect the immune system from the ill effects of
emotional stress. An experiment may show that extreme grief
depresses human T cells, for instance, but we don't know if the
rest of the system is harmed, or whether the fluctuation means
much.
Still, reports of increased illness and even death among the
recently bereaved are common. Cancer patients with a "fighting
spirit" seem to live longer than those who are despondent, but
this may or may not prove something about immune function. Good
social support is thought to improve immunity in people under
stress.
Immune cells and nerve cells do interact. For example, when
fighting an infection, immune cells are able to stimulate the
brain to transmit the impulses that produce fever. Receptors for
many of the chemicals released during stress, such as epinephrine
and norepinephrine, have been observed on the surface of
lymphocytes found near nerve terminals in the lymph nodes and
spleen. This suggests that what goes on in the brain can interact
with the immune system to suppress or, conversely, enhance it.
What does smoking do to
immunity?
Part of the reason smokers are at risk for lung cancer and
respiratory diseases is that smoking suppresses immune cells. When
smokers quit, immune activity begins to improve within 30 days.
When and why does the immune
system malfunction?
The immune system has so many built-in fail-safes that, in theory
at least, we should rarely fall ill. But, in fact, we do. Harmful
agents such as HIV can baffle our defenses. The system can simply
be overwhelmed by the number and toxicity of viruses, bacteria, or
other foreign cells and toxins.
Though the immune system defends us against cancer, it is subject
to cancer. Leukemia is a cancer of the white blood cells; multiple
myeloma affects certain lymphocytes that produce antibodies.
Cancers of the lymph system include lymphoma and Hodgkin's
disease. Some of these cancers can now be successfully treated.
Sometimes the gatekeepers of the system go crazy, mistaking a
basically inoffensive intruder such as pollen, dust, or a bit of
bee venom for an enemy and causing the body to go into the red
alert known as an allergic reaction. In addition, the immune
system can mistake the body's own cells and tissues for "non self"
and attack them, as in auto-immune diseases like rheumatoid
arthritis and systemic lupus.
The immune system will also reject and kill potentially lifesaving
organ and tissue transplants, unless some way can be found to
circumvent the reaction. Though in theory a pregnant woman's
immune system should attack the fetus—which is non self—it
doesn't. This is because the fetus itself produces a substance
that shields it from the maternal defense system.
So how can I nurture my
immune system?
Perhaps the most direct action you can take is to consume a
varied, balanced diet of vegetables, fruits, whole and fortified
grains, and dairy products, with amounts of fish and meat. A basic
daily multivitamin/mineral supplement is usually a good idea.
Herbs such as Astragalus and Echinacea are appropriate choices to
support the immune system.
Regular moderate exercise is associated with good health and
longevity and will benefit your cardiovascular system, whether it
boosts immunity or not. Getting adequate sleep is also helpful.
And, of course, don't smoke. |
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