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The Blood & Circulation The Lymphatic System The 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
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 radiotherapy can both cause lowering of your neutrophil count. So after each chemotherapy treatment, or a course of 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.
Your cancer specialist may want you to take antibiotics when your blood counts are low. This is to help prevent severe infection. We don't really know whether this approach works but it is soon to be tested in a clinical trial.
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'. A small amount of protein from a disease is given. 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.
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 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.
Can the immune system cure cancer?
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.
What about immunotherapy?Immunotherapies are treatments that boost your immune system. They are used in cancer treatment because cancer cells are different from normal cells and so are picked up by the immune system.
Many different chemicals that are used in the immune response can now be made in the laboratory. You may have heard of one or two of these:
Interferon Interleukin 2 (IL2) Interferon-alpha and Interleukin 2 might act by boosting the immune response to help the body kill off cancer cells.
Scientists are also trying to develop vaccinations against cancer cells. Possibly the immune system can be trained to see cancer cells as being invaders and kill them.
Monoclonal antibodiesMonoclonal 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 antibody is 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
RituximabTM recognises CD20 protein on the outside of non-Hodgkin's lymphoma cells ADEPT is a treatment using antibodies that recognise colon cancer cells 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 experimental at the moment and are only being tested for a few types of cancer. Look in our clinical trials database for monoclonal antibody trials - type 'antibody' in the free text search box. This is exciting new research because it may be possible to kill cancer cells without damaging other body cells. But it may take a long time to develop further because it is so complicated to do.
Stress, the immune system and cancer
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 does weaken 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, for example, can be very relaxing.
Avoid getting run down by looking after yourself
Eat a balanced diet when you are able Try to eat fresh food whenever possible Get plenty of rest - even if you cannot sleep, you can rest