The immune system
This page tells you about the immune system. There is information on
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 blood 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
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
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 centre or go to Accident and Emergency (A&E) straight away
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.
You can ask your cancer doctor or nurse what precautions you should take against infection. There are also some tips in our cancer drug side effects section.
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 an 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.
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.
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.
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.
Immunotherapy is a type of biological therapy. Biological therapies use natural body substances or drugs made from natural body substances to treat cancer. Immunotherapies are treatments that use your immune system. They are used in cancer treatment because cancer cells are different from normal cells and so can be picked up by the immune system.
Many different chemicals that are produced as part of the immune response can now be made in the laboratory. You may have heard of one or two of these
Interferon-alpha and Interleukin 2 act by boosting the immune response to help the body kill off cancer cells.
Scientists are also trying to develop vaccinations against cancer cells. It may be possible for them to help the immune system to be trained to see cancer cells as being invaders and kill them.
Monoclonal antibodies are made in the laboratory. The scientists developing them make an antibody with a variable end that recognises cancer cells. 'Monoclonal' just means that all the antibodies are exactly the same type, with the same variable end.
The monoclonal antibodies recognise molecules on the outside of cancer cells. Different antibodies have to be made for different types of cancer, for example
- Rituximab (Mabthera) recognises CD20 protein on the outside of some lymphoma cells
- Bevacizumab (Avastin) targets growth factors that help blood vessels grow and is used to treat bowel cancer, breast cancer and some other cancers
- Trastuzumab (Herceptin) recognises breast cancer cells that produce too much of the protein HER 2 - these cancers are called HER 2 positive
The constant end of cancer treating monoclonal antibodies kills the cancer cells by marking them so other immune system cells pick them out. The job of these other cells is to find antibody labelled cells and kill them. But the scientists can make the monoclonal antibody even better at killing cancer cells by attaching
- A radioactive atom that delivers radiation directly to the cancer cells
- A chemotherapy drug that is taken straight to the cancer cells by the monoclonal antibody
Monoclonal antibodies are still being researched but are now used for more and more types of cancer. Look in our clinical trials database for monoclonal antibody trials - type 'antibody' into the free text search box. This is an exciting new area of cancer treatment. There is a lot of research going on into the use of immune system therapies to treat cancers. There is detailed information about this in the biological therapies section of CancerHelp UK. You can also look in the treatment section of the type of cancer you are interested in.
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. This 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.
You can avoid getting run down and look after yourself by
- Eating a balanced diet when you are able
- Trying to eat fresh food whenever possible
- Getting plenty of rest - even if you find it hard to sleep, you can rest
- Doing gentle exercise if you are able
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