The immune system protects the body against infection caused by bacteria, viruses, fungi
or parasites. It is really a collection of reactions and responses that the body makes to
infection. So it is sometimes called the 'immune response'.

The immune system is important to cancer patients in many ways because
•The cancer can weaken the immune system
•Cancer treatment can weaken the immune system
•The immune system may help to fight your cancer

Cancer can weaken the immune system by spreading into the bone marrow where the cells
that help fight infection are made. This happens most often in leukaemia or lymphoma.
But it can happen with other cancers too. The cancer in the bone marrow stops the bone
marrow making so many blood cells.

Chemotherapy and radiotherapy can weaken immunity by causing a drop in the number of
white blood cells made in the bone marrow. Apart from bone marrow transplants or stem
cell transplants, this effect on the bone marrow is temporary. High doses of steroids
can also weaken your immune system temporarily.

Some cells of the immune system can recognise cancer cells as abnormal and kill them.
Unfortunately, this is not enough to get rid of a cancer altogether. But some new treatments
aim to use the immune system to fight cancer. There are two main parts of the immune system
•The in-built protection we have from birth
•The immune protection we develop from being exposed to certain diseases

In-built immune protection

This is also called 'innate immunity'. These immune mechanisms are always ready and prepared
to defend the body from infection. They can act immediately (or very quickly). This in-built
protection comes from
•A barrier formed by the skin outside the body
•Inner linings of the gut and lungs which produce mucus and trap invading bacteria
•Hairs which move the mucus and trapped bacteria out of the lungs
•Stomach acid which kills bacteria that have been swallowed
•Helpful bacteria growing in the bowel which prevent other bacteria from taking over
•Urine flow which flushes bacteria out of the bladder and urethra
•White blood cells called 'neutrophils' which can find and kill bacteria and other
   infectious organisms

The skin forms a waterproof mechanical barrier. But it is also slightly acidic.
This helps to keep bacteria out as they don't like acid. Some skin conditions cause
loss of this acidity and people are then much more prone to skin infections.

There are several ways that these natural protection mechanisms can be damaged or overcome
if you have cancer. For example
•Something may break the skin barrier (such as having a drip in your arm
  or a wound from surgery)
•Chemotherapy may damage to the lining of the gut (severe diarrhoea
  caused by some chemotherapy drugs can break down the gut lining)
•A catheter into your bladder can become a route for bacteria to get inside
  the bladder and cause infection
•Radiotherapy to the lung can damage the hairs and mucus producing cells
  that help to remove bacteria
•Antacids for heartburn may neutralise the stomach acid that kills bacteria
•Chemotherapy can temporarily reduce the number of neutrophils in the
  blood (the 'neutrophil count') which means it is more difficult
  for you to fight off infection.

Neutrophils-These white blood cells are very important for fighting infection.Neutrophils-These
white blood cells are very important for fighting infection.
They can
•Move to areas of infection in the body
•Stick to invading bacteria or fungi
•Swallow up the bacteria, viruses or fungi causing the infection
•Kill the bacteria they have swallowed with chemicals
Your normal neutrophil count is between 2,000 and 7,500 per cubic millimetre of blood.
When you don't have enough neutrophils you are said to be neutropaenic.

Chemotherapy and some radiotherapy treatments can lower your neutrophil count.So, after
chemotherapy or radiotherapy you may be more likely to get bacterial or fungal infections
(like thrush).If you are having cancer treatment, it is important for you to know that
•Infections can become serious more quickly in people with low neutrophil counts
•Antibiotics could save your life, so if you get a fever or feel ill, phone your
   cancer doctor straight way
You are most likely to become ill from bugs you carry around with you normally,
not from catching someone else's. This means that you don't have to avoid your family,
friends or children when you are sent home after chemotherapy.

When your blood counts are low, your cancer specialist may want you to take antibiotics
to help prevent severe infection. There is some debate about whether this is useful.
In the Significant Trial, some people had antibiotics during treatment and some had a dummy
tablet (placebo). The results showed that fewer people who had antibiotics during
treatment had a fever or had to go to hospital for treatment for an infection.

Acquired immunity

This is immune protection the body learns from being exposed to diseases. The body learns
to recognise each different kind of bacteria and virus it meets for the first time.
The next time that particular bug tries to invade the body; the immune system is ready for
it and able to fight it off more easily. This is why you usually only get some infectious
diseases once - for example, measles or chicken pox.

Vaccination works by using this 'immune memory'. The vaccine contains a small amount of protein
from a disease. This is not harmful, but it allows the immune system to recognise the disease
if it meets it again. The immune response can then stop you getting the disease. Some vaccines
use tiny amounts of the live bacteria or virus. These are called live attenuated vaccines.
Attenuated means; that the virus or bacteria has been changed so that it will stimulate the
immune system to make antibodies but won't cause the infection. Other types of vaccine use
killed bacteria or viruses, or chemicals produced by bacteria and viruses.

B cells and T cells

The white blood cells involved in the acquired immune response are called 'lymphocytes'. There
are two main types of lymphocytes - B cells and T cells. B and T lymphocytes are made in the
bone marrow, like the other blood cells. They have to fully mature before they can help in the
immune response. B cells mature in the bone marrow. But the immature T cells travel through the
blood stream to the thymus gland where they become fully developed. Once they are fully mature
, the B and T cells travel to the spleen and lymph node ready to fight infection.

B cells react against invading bacteria or viruses by making proteins called antibodies. The
antibody made is different for each different type of bug. The antibody locks onto the surface
of the invading bacteria or virus. The invader is then marked with the antibody so that the
body knows it is dangerous and it can be killed off. Antibodies can also detect (and kill)
damaged cells.

The B cells are part of the memory of the immune system. The next time the same bug tries to
invade, the B cells that make the right antibody are ready for it. They are able to make
their antibody very quickly.

Antibodies are proteins made by the B cells. They have two ends. One end sticks to proteins
on the outside of white blood cells. The other end sticks to the germ (or damaged cell) and
helps to kill it. The end of the antibody that sticks to the white blood cell is always the
same. So it is called the constant end. The end of the antibody that recognises germs and
damaged cells varies depending on the cell it is designed to recognise. So it is called the
variable end. Each B cell makes antibodies with a different variable end from other B cells.
Cancer cells are not normal cells. So some antibodies with variable ends recognise cancer
cells and stick to them.

There are different kinds of T cells called
•Helper T cells
•Killer T cells
The helper T cells stimulate the B cells to make antibodies, and help killer cells develop.

Killer T cells kill the body's own cells that have been invaded by the viruses or bacteria.
This prevents the bug from reproducing in the cell and then infecting other cells.

Your immune system is very unlikely to be able to fight off an established cancer
completely without help from conventional cancer treatment, although there are very
rare documented cases of cancers just disappearing (spontaneous regression). Some
treatments use elements of the immune system to help treat cancer. mmunotherapy is
the some kind of biological therapy.

Many people with cancer believe that they should strengthen their immune systems to help
beat the disease. There is a commonly held belief that reducing stress can help to
strengthen our immune systems. is the thinking behind some complementary therapies, using
relaxation techniques for instance.

There is some scientific evidence that stress weakens our immunity. Two studies looking at
whether stress affected cancer recurrence had conflicting results. While no one knows
whether strengthening immunity can help to cure cancer, most doctors and nurses agree that
reducing stress is a good thing to do. While many life stresses cannot be avoided
altogether, there are ways of trying not to let things get to you. Many complementary
therapies such as meditation, massage and reflexology, can be very relaxing.

We can avoid getting run down and look after our self by
•Eating a balanced diet when we are able
•Trying to eat fresh food whenever possible
•Getting plenty of rest - even if we find it hard to sleep, we can rest