What is the immune system?

Your immune system defends your body from infection. It is made up of a complex network of cells, chemicals, tissues and organs. An underactive or overactive immune system can cause health problems.

Your immune system recognises 'invaders' such as bacteria, viruses and fungi, as well as abnormal cells like cancer cells. It creates an immune response and helps your body fight invasion.

When harmful germs enter your body, you produce special white blood cells to fight the infection. The white blood cells identify the germ and produce antibodies (special proteins) to fight it. Afterwards, your white blood cells can 'remember' the germ and how to fight it.

'Remembering' the attack is important when your body is exposed to the same germ in the future. It is also important for understanding how vaccines work. Vaccines expose your immune system to a dead or weakened germ or to proteins from a germ. Your body can recognise and respond very quickly to any future exposure to the same germ.

What are the parts of my immune system?

Your immune system involves many parts of your body. Each part plays a role in recognising germs, communicating with other body parts and working to fight the infection.

Parts of your immune system include your skin, bone marrow, thymus, lymphatic vessels, lymph nodes, spleen and mucous membranes.

Your immune system involves different types of cells, such as lymphocytes. These are white blood cells that mature to become T cells and B cells. B cells make antibodies and T cells fight foreign substances in the body.

How does my immune system work?

The many different parts of your immune system work together in different ways. This is how they work:

• Skin — your skin is your first line of defence and helps keep germs out of your body.
• Bone marrow — this produces blood cells such as lymphocytes.
• Thymus gland — this is a gland in your upper chest where some immune cells mature.
• Lymphatic vessels — a network of tiny vessels that allows immune cells to travel through the body in a fluid called lymph.
• Lymph nodes — lymph nodes are small lumps of tissue in your groin, armpits, neck and other areas that drain and filter lymph fluid.
• Spleen — this is an organ under your ribs on your left side that filters germs from the blood.
• Mucous membranes — the lining inside your mouth, nose and other areas can trap germs from the environment and allow your immune cells to catch and attack them.

What immune conditions are there?

There are many different immune conditions. They can occur if your immune system is underactive or overactive.

Overactive immune system

Sometimes your immune system can overreact to something in the body or environment. This can cause:

• allergies — when your immune system responds to something considered harmless for most people, such as pollen or a certain food.
• autoimmune conditions — when your immune system gets confused and attacks a healthy part of your body, causing damage. Examples include multiple sclerosis and rheumatoid arthritis.

Underactive immune system (immunodeficiency)

Sometimes your immune system doesn't work properly and can't protect your body as it should. This can increase your chance of infection. If you have immunodeficiency, your body does not fight infection as it should.

You may be born with an immunodeficiency, or get it from a medical treatment or another health condition.

Visit the Immune Deficiencies Foundation Australia (IDFA) website for more information about immunodeficiency.

What are some of the symptoms of immune conditions?

If you have an immunodeficiency, you may have one or more of the following symptoms:

• poor growth (in children)
• recurrent or severe infections that may not get better with regular treatment, such as pneumonia, sinusitis, skin abscess or meningitis
• infections caused by unusual germs
• chronic diarrhoea
• oral thrush

If you have allergies, you may have some of the following symptoms:

• swelling of your lips, tongue, face and eyes
• difficulty breathing
• a rash with hives or welts
• abdominal (tummy) pain and vomiting

If you have an autoimmune condition, the symptoms will vary depending on what part of your body is affected.

How can I support my immune system?

There are several actions you can take to boost your immune system, including:

• doing some physical activity
• quitting smoking
• keeping a healthy and balanced diet
• avoiding drinking too much alcohol

Resources and support

• Read more about your immune system at Australasian Society of Clinical Immunology and Allergy (ASCIA).
• For tips on keeping your immune system healthy, read this article from Heart Research Australia.
• The Baker Institute has tips on food and your immune system.
• You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.

Languages other than English

• Find information about vaccinations for adults and children in several community languages.

Information for Aboriginal and/or Torres Strait Islander peoples

• Visit Vaccination for Our Mob for information about illnesses that can be prevented by vaccination.
• Find out about vaccinations for Aboriginal and/or Torres Strait Islander people.