• The immune system fights infection.
  • It keeps a record of every microbe defeated.
  • Other lines of defence include the skin, lungs and digestive tract.

The immune system is made up of special cells and chemicals that fight infection. The white blood cells that make up the immune system are made in the bone marrow. These cells move through blood and tissue. Every time a microbe (germ) is overcome, the immune system remembers that microbe. If the body comes in contact with that microbe again, it will be defeated quickly.

The immune system also produces proteins called antibodies that can help neutralise infection or the toxins that some germs produce.

The response to a cut

When skin is broken, microbes can enter the cut. The immune system sets up a defence to this invasion, which includes the following:
  • White blood cells, which circle the bloodstream, ‘hear’ of the breach via a chemical alarm sent out by damaged cells. The white blood cells move to the cut and start ‘eating’ the bacteria. Pus is actually dead microbes and dead white blood cells.
  • Lymphocytes are another type of immune system cell. B-lymphocytes try to identify the microbe. If the microbe has been defeated before, the lymphocytes know which antibodies have to be made in order to kill it.
  • There are a number of different T-lymphocytes. Helper cells help the B-lymphocytes to make antibodies. Killer cells attack infection. Suppressor cells help to call a halt to the immune system response.

The lymphatic system

The lymphatic system is part of the immune system. It is made up of lymph nodes that trap microbes, and the spleen (a blood-filtering organ). Lymphocytes are also found in the lymphatic system.


A rise in body temperature, or fever, can happen with some infections. This is actually an immune system response. A rise in temperature can kill some microbes. Fever also triggers the body’s repair process.

Viral infections

The immune system keeps a record of every microbe it has ever defeated. This means it can destroy the microbe quickly if it enters the body again, before it can multiply and make you feel sick.

Some infections, like influenza and the common cold, have to be fought many times, because so many different viruses can cause these illnesses. Catching a cold from one virus does not give you immunity against the others.

Immunisation and HALO

Immunisation works by mimicking the body’s natural immune response. A small amount of the specially treated virus, bacterium or toxin (vaccine) is injected into the body. The body then makes antibodies. If a vaccinated person is exposed to the actual virus, bacterium or toxin, they won’t get sick. Vaccinations are available against many diseases, such as measles and tetanus.

The immunisations you may need are decided by your health, age, lifestyle and occupation. Together, these factors are referred to as HALO.

HALO is defined as:
  • Health – some health conditions or factors may make you more vulnerable to vaccine-preventable diseases. For example, premature birth, asthma, diabetes, heart, lung, spleen or kidney conditions, Down syndrome and HIV will mean you may benefit from additional or more frequent immunisations.
  • Age – at different ages you need protection from different vaccine-preventable diseases. Australia’s National Immunisation Program sets out recommended immunisations for babies, children, older people and other people at risk, such as Aboriginal and Torres Strait Islanders. Most recommended vaccines are available at no cost to these groups.
  • Lifestyle – lifestyle choices can have an impact on your immunisation needs. Travelling overseas to certain locations, planning a family, sexual activity, smoking, and playing contact sport that may expose you directly to someone else’s blood, will mean you may benefit from additional or more frequent immunisations.
  • Occupation – you are likely to require additional or more frequent immunisations if you work in an occupation that exposes you to vaccine-preventable diseases or puts you into contact with people who are more susceptible to problems from vaccine-preventable diseases such as babies or young children, pregnant women, the elderly, and people with chronic or acute health conditions. Workers in aged care, childcare, healthcare, emergency service or sewerage repair and maintenance need to discuss their immunisation needs with their doctor. Some employers help with the cost of relevant vaccinations for their employees.
View the HALO graphic (PDF) to find out more.

Other defences

As well as the immune system, the body has a number of other ways to defend itself against microbes, including:
  • Skin – is a waterproof barrier that secretes oil with bacteria-killing properties
  • Lungs – mucous (phlegm) traps particles, and small hairs (cilia) wave the mucous upwards so it can be coughed out.
  • Digestive tract – the mucous lining contains antibodies, while the acid in the stomach can kill most microbes.
  • Other defences – body fluids like skin oil, saliva and tears contain anti-bacterial enzymes that help reduce the risk of infection. The constant flushing of the urinary tract and the bowel can also help.

Common problems

Some common problems of the immune system include:
  • Allergies – the immune system reacts to a harmless substance as if it were harmful. Allergenic substances include pollen, dust or animal proteins. Common allergies include hay fever, asthma and allergic reactions to food.
  • Autoimmunity – the immune system attacks the body’s own structures as if they were foreign.
  • Lupus erythematosus – symptoms include skin rashes and painful joints. This is an autoimmune disease.
  • Rheumatoid arthritis – the immune system attacks the joint, causing inflammation and swelling.

Where to get help

  • Your doctor
  • A specialist (ask your doctor for a referral – this may be a dermatologist, rheumatologist or immunologist)

Things to remember

  • The immune system fights infection.
  • It keeps a record of every microbe defeated.
  • Other lines of defence include the skin, lungs and digestive tract.

More information

Immune system

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Autoimmune disorders

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This page has been produced in consultation with and approved by: Australasian Society of Clinical Immunology and Allergy (ASCIA)

Last updated: March 2015

Page content currently being reviewed.

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.