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About the immune system

The immune system protects the body from infections. When a foreign organism such as a germ enters the body, or when a cell becomes abnormal, the immune system usually recognises and then attacks it so that it doesn’t harm the body. This process is called an immune response.

The immune system can remember every germ or abnormal cell it has attacked so it can easily recognise it if it enters the body again.

The parts of the immune system

The immune system is made up of a network of cells, chemicals, tissues and organs. White blood cells known as lymphocytes are part of the immune system. They travel throughout the body looking for germs and abnormal cells. There are two main types of lymphocytes:

T-cells – recognise and destroy germs and abnormal cells. T-cells also help control and direct the activity of the immune system.

B-cells – make proteins called antibodies. An antibody can lock onto the surface of the invading germ. This helps T-cells recognise the germ.

The organs of the immune system help to make, filter and process lymphocytes. These organs include the:

  • lymph nodes – small structures found in groups throughout the body and linked by lymph vessels
  • spleen – a large organ in the abdomen
  • thymus – a gland behind the breastbone
  • tonsils – two small organs at the back of the throat
  • bone marrow – the spongy material inside bones.

Cancer and the immune system

Cancer starts when abnormal cells begin growing out of control. The immune system usually prevents cancers from developing because it recognises abnormal cells and destroys them. In some cases, the natural immune response is not strong enough to kill all abnormal cells and they develop into cancer.

Cancer cells also find ways to stop the immune system destroying them – for example, by setting up barriers (“checkpoints”) so the immune system can’t reach them, or by changing over time (mutating) to avoid being recognised by T-cells and antibodies.

The role of the immune system

The immune system has to be carefully balanced to keep you healthy – if it is too weak, you will be prone to infection and disease; if it is too active, it can start to attack normal cells (as in autoimmune diseases such as rheumatoid arthritis).

Tipping the balance – Cancers find ways to tip the balance of the immune system so that it does not attack the cancer. Immunotherapy tips the balance back in favour of the immune system, helping it to fight the cancer.

Immune side effects – If immunotherapy tips the balance of the immune system too far and makes it too active, you can get side effects anywhere in the body.

Over time – Because the immune system has a “memory”, immunotherapy sometimes keeps working long after treatment finishes, but side effects can also appear months or even years after treatment.

Conditions affecting immune response – It is important to tell your cancer specialist if you have an autoimmune disease such as rheumatoid arthritis or lupus or if you’ve had an organ transplant. You may still be able to have immunotherapy, but it could be more difficult. Autoimmune diseases make the body’s immune system overactive so it attacks normal cells, leading to symptoms such as inflammation, swelling and pain. The extra immune system activity caused by immunotherapy can make these symptoms worse. After an organ transplant, most people take drugs that suppress the immune system to stop the body
rejecting the new organ. Your specialists will need to carefully balance these drugs with the extra immune system activity caused by immunotherapy.

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Understanding Immunotherapy

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This information is reviewed by

This information was last reviewed July 2019 by the following expert content reviewers: A/Prof Brett Hughes, Senior Staff Specialist, Medical Oncology, Royal Brisbane and Women’s Hospital and The Prince Charles Hospital, and Associate Professor, The University of Queensland, QLD; Dawn Bedwell, 13 11 20 Consultant, Cancer Council Queensland, QLD; Tamara Dawson, Consumer; A/Prof Craig Gedye, Senior Staff Specialist, Medical Oncology, Calvary Mater Newcastle, and Conjoint Associate Professor, School of Medicine and Public Health, University of Newcastle, NSW; A/Prof Alexander Menzies, Medical Oncologist, Associate Professor of Melanoma Medical Oncology, and Faculty Member, Melanoma Institute Australia, The University of Sydney, Royal North Shore Hospital and Mater Hospital, NSW; Dr Donna Milne, Nurse Consultant Melanoma and Skin Service, Peter MacCallum Cancer Centre, VIC; Dr Geoffrey Peters, Staff Specialist, Medical Oncology, Canberra Hospital and Health Services, and Clinical Lecturer, Australian National University, ACT.