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.

Learn more about:

Listen to a podcast on New Cancer Treatments – Immunotherapy and Targeted Therapy

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.

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.

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 balance icon

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 icon

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 icon

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.

Click on the icon below to download a PDF booklet on Immunotherapy.

Printed copies are available for free - Call 13 11 20 to order

Instructions for downloading and reading EPUB files

Apple devices

The iBooks application must be installed on your Apple device before you can read the EPUB.
Different ways to download an EPUB file to your Apple device:

  • email EPUB files to yourself and transfer the attachment to iBooks.
  • copy EPUB files into DropBox (or a similar service) and use the DropBox app to send them to iBooks.
  • open EPUB files directly from Mobile Safari and open them in iBooks, where they are saved automatically by downloading the EPUB from the website.

Need more help? Visit:


To download an EPUB file to your Kobo from a Windows computer:

  • download and save the EPUB directly onto your desktop.
  • connect your Kobo to your computer using the USB cable and tap “Connect” on your eReader.
  • select “Open folder to view files” to view the contents of your Kobo.
  • navigate to where you have stored your EPUB file in “Finder”, in documents or downloads, and drag and drop it into the Kobo window. You can now disconnect your Kobo to read the eBook.

To download an EPUB to your Kobo from a Mac:

  • download and save the EPUB directly onto your desktop.
  • connect your Kobo to your computer using the USB cable and tap “Connect” on your eReader.
  • open your “Finder” application.
  • select “Kobo eReader” from the listed devices to view the contents of your Kobo.
  • navigate to where you have stored your EPUB file in “Finder”, probably in documents or downloads, and drag and drop it into the Kobo window. You can now disconnect your Kobo to read the eBook.

Turn on your Kobo and your EPUB will be located in “eBooks”, while a PDF will be located in “Documents”.
Need more information? Visit:

Sony Reader

To download an EPUB file on your Sony Reader™:

  • ensure you have already installed the Reader™ Library for PC/Mac software
  • select the eBook you want from our website and click the link to download it.
  • connect the Reader™ to your computer.
  • open the Reader™ Library software and click “Library” in the left-hand pane and select the eBook to view it.

Need more help? Visit:

Amazon Kindle 2nd Generation devices

EPUB files can’t be read on the Amazon Kindle™. However, like most eReaders, Kindle™ 2nd Generation devices are able to display PDFs. We recommend that you download the PDF version of this booklet if you would like to read it on a Kindle™.
To transfer a PDF to your Kindle™ via USB cable from your computer or Mac:

  • download the PDF directly onto your computer.
  • connect the USB cable to your computer’s USB port, and the micro USB end of the cable to your Kindle™. Note: the Kindle™ won’t be available as a reading device while it is connected to your computer until it has been disconnected.
  • open the Kindle™ drive and several folders will appear inside. The “Documents” folder is where you will need to copy or drag the PDF to.
  • safely eject your Kindle™ from your computer and unplug the USB cable. Your content will appear on the Home Screen.

Kindle also provides a Kindle Personal Documents Service that allows users to send documents as an attachment directly to your eReader. For more information on this service, visit
For more information on accessing a PDF on your Kindle™, visit, log in to your account and click on Personal Document Settings.
Need more help? Visit

Android and PC

You can also download and open eBooks on Android devices and PCs with appropriate apps or software installed. Suitable eReader apps for Android include Google Play Books, FBReader and Moon+ Reader. Suitable software for PCs include Calibre and Adobe Digital Editions.

This information was last reviewed in July 2019
View who reviewed this content
View our editorial policy

Support services

Coping with cancer?
Ask a health professional or someone who’s been there, or find a support group or forum

Need legal and financial assistance?
Pro bono legal and financial matters, no interest loans or help with small business

Cancer information

Other cancer treatments
Learn more about other cancer treatments, such as chemotherapy, radiation therapy, surgery and targeted therapy

Living with advanced cancer
Coping with cancer that has spread and making treatment decisions

View our publications
Guides and fact sheets for people with cancer, their families and friends