The Body's Natural defences
defence force, the immune system, is designed to protect us from
illness. So how does it work and why does it sometimes fail ?
immune system protects us from infection and invasion by all sorts of
bacteria, viruses, fungi and parasites. There are two basic defence
forces against these micro-organisms: white blood cells and the
specially-tailored proteins they release called antibodies.
HOW ANTIBODIES WORK
White blood cells patrol the body in the bloodstream, passing into the
body tissues through tiny blood vessels called capillaries. The cells
drain back into the lymph vessels, a network-like blood system
connecting the lymph glands. The lymph glands are the power houses of
the immune system, and include the tonsils, the spleen and the small
lumps situated in the neck, under the arm and in the groin which swell
during an infection.
When the immune system recognizes an alien substance (called an
antigen because it provokes the production of antibodies), it usually
takes from two to three days to begin to respond. Then, the immune cells
race to duplicate the speed of the micro-organisms as they swiftly begin
to multiply and spread in their millions throughout the system. Given
time, the body usually wins. But if we're exposed again to the same
antigen, the response is much faster and the invader is swiftly
overwhelmed. This is why we rarely suffer twice from the same disease.
ROLE OF WHITE BLOOD CELLS
There are three main types of white blood cells playing a part in the
body's defence - the lymphocytes, the leucocytes and the monocytes.
Lymphocytes are the most important cells of the immune system and there
are two main types: B and T cells - so called because they are produced
and mature in the bone marrow and in the thymus.
B-cells come in an infinite range, each kind making just one type of
antibody. During an infection, the B-cell that forms the appropriate
antibody multiplies, making copies of itself to fight the invader. Some
of these B-cells live for many years, ready to respond again to the same
they are the prime defence against viruses, which are not so easily
attacked by antibodies. T-cells also attack foreign tissue and are
responsible for the rejection of transplanted organs.
The circulating protein antibodies made by B-cells are called
immunoglobulins. There are five main types of immunoglobulins - IgA, IgD,
IgE, IgG and IgM - which all have different functions in the battle
against foreign bodies.
IgA is the most important defence against bacteria and viruses in the
blood and other secretions. It deals with cold viruses, influenza and
the bacteria causing pneumonia. It also kills the viruses which get into
the intestine, such as the polio virus. IgD is thought to control the
activity of other cells, while IgE protects mucous surfaces and is
involved in the allergic response in conditions such as asthma, eczema
and hay fever. IgG is the major immunoglobulin in blood and is quickly
manufactured to fight invaders. IgM appears slowly after an infection,
but it remains in the bloodstream for a very long time.
A strong immune system means you're less likely to become ill and
will recover more quickly if you do.
WHEN IT GOES WRONG
An underactive immune system makes you prone to infection. This is
called immunodeficiency - when there are too few lymphocytes or too few
antibodies produced. A weakened immune system can be caused by
malnutrition and infections such as measles and glandular fever, or
viruses such as HIV.
Sometimes the immune system goes wrong and starts attacking itself.
This results in auto-immune diseases such as rheumatoid arthritis,
systemic lupus erythematosus and insulin-dependent diabetes.