Immune system

Long-term over-activation of the immune system may be the single most important cause of cancer, say experts.

When the immune system goes into over-drive it leads to inflammation of the tissues. However, a new report suggests that the importance of this role may have previously been under-estimated.

The authors argue that long-standing over-activation of the immune system is the key event in the genesis of many forms of the disease.

Tissues become inflamed when the immune system is kicked into action by injury, infection or an allergic reaction.

White blood cells and molecules involved in the immune response are produced to fight off infection and aid the healing process.

But the same molecules that stimulate the regeneration of damaged tissues may also play a part in the birth of cancer and accelerate its growth and spread.

The researchers argue that continually switching on the immune system encourages cancer in a number of ways:

• Immune cells that would normally kill developing cancer cells can be switched off.
• Immunity for healthy cells can be spread to cancer cells too.
• Blood vessel growth is stimulated, providing nutrition for cancer cells
• Many immune system molecules are extremely chemically reactive, and may actually cause cancerous mutations by attacking DNA.

The researchers believe that nearly all carcinogens work by over-cooling the immune system. For instance, tobacco smoke can cause long-term inflammation.

They also believe that cancer might cause inflammation too, thus creating the conditions needed to boost the growth and spread of the disease.

What about herbal immunotherapy?

Immunotherapy’s are treatments that boost your immune system. Herbal medicines are used in cancer treatment because cancer cells are different from normal cells and so are picked up by the immune system.

Immune System

The immune system protects the body against infections by bacteria, viruses and other parasites. It is really a collection of 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

The cancer can weaken the immune system by invading 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.

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 or stem cell transplants, this effect on the bone marrow is temporary.

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 inbuilt protection we have from birth
• The immune protection we acquire from being exposed to certain diseases

Inbuilt immune protection

This can be 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 inbuilt protection comes from

• The skin outside the body and other lining tissues inside forming a barrier
• Mucus lining of the gut and lungs which traps 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 agents

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 if you have cancer
• Something that breaks the skin barrier such as a drip or a wound from surgery
• Chemotherapy damage to the lining of the gut (for example if you have had a lot of diarrhoea as a side effect)
• A catheter into your bladder (bacteria can 'climb' the catheter and get inside the bladder causing infection)
• Radiotherapy to the lung which can temporarily damage the hairs and mucus producing cells that help to remove bacteria
• Antacids for heartburn which 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. They are good at fighting bacteria and fungal infections. They can
• Move to sites of infection in the body
• Stick to invading bacteria or fungi
• Swallow up the invader
• Kill the bacteria they have swallowed with chemicals
Your normal neutrophil count is between 3,000 and 6,000 neutrophils in each millilitre of blood. When you don't have enough neutrophils you are said to be 'neutropaenic'.

Chemotherapy and some radiotherapy treatments can cause lowering of your neutrophil count. So after chemotherapy or radiotherapy you may be more prone to bacterial or fungal infections (like thrush).

If you are having cancer treatment, it is important for you to know that
• Infections can move fast in people with low neutrophil counts
• Antibiotics could save your life, so if you get a fever phone your cancer centre or go to casualty straight away
You are most likely to become unwell 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.

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 bug tries to invade the body, the immune system is ready for it and better able to fight it off. 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 nodes ready to fight infection.

What do B cells do?

B cells react against invading bacteria or viruses by making proteins called antibodies. The antibody made is different for each different 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.

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 more quickly than the first time the bug invaded.

What are antibodies?

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 and helps to kill the germ or damaged cell. 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 there will be some antibodies with variable ends that recognise cancer cells and stick to them.

What do T cells do?

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.

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