Healthdirect Free Australian health advice you can count on.

Medical problem? Call 1800 022 222. If you need urgent medical help, call triple zero immediately

healthdirect Australia is a free service where you can talk to a nurse or doctor who can help you know what to do.

beginning of content

Immune system

Your body's immune system is designed to protect you from, or get rid of, infection. It is made up of a complex network of cells, tissues and organs in your body. An underactive or overactive immune system can cause health issues.

What is the immune system?

The immune system comprises:

  • skin
  • bone marrow
  • the thymus, a gland in your upper chest
  • white blood cells, which fight infection
  • lymph, a milky fluid carrying white blood cells
  • the lymphatic system, a network of tiny vessels that carry lymph around the body
  • lymph nodes, small lumps in your groin, armpit, around your neck and elsewhere
  • the spleen, an organ under your ribs on the left
  • mucous membranes, like the lining of the inside of your mouth.

The lymphatic system allows immune cells to travel between tissues and the bloodstream. The lymphatic system contains lymphocytes (mostly T cells and B cells), which try to recognise any bacteria, viruses or other foreign substances in your body and fight them.

Lymph nodes are found in certain areas such as the base of the neck and the armpit. They become swollen or enlarged in response to an infection.

How does the immune system work?

The skin and mucous membranes are the first line of defence against bacteria, viruses and other foreign substances. They act as a physical barrier, and they also contain immune cells.

When your skin has a cut, microbes can enter your body. The cut triggers certain immune cells in the bloodstream that try to destroy the invaders.

In an infection, white blood cells identify the microbe, produce antibodies to fight the infection and help other immune responses to occur. They also 'remember' the attack.

This is how vaccinations work – vaccines expose your immune system to a dead or weakened virus, so that your body is able to respond very quickly to any future exposure to the same virus.

Related conditions

Overactivity of the immune system is related to disorders such as allergies and autoimmune diseases.

Allergies involve an immune response to something considered harmless in most people, such as pollen or a certain food.

Autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, occur when your immune system attacks normal components of the body.

Underactivity of the immune system, or immunodeficiency, can increase your risk of infection. You may be born with an immunodeficiency or acquire it due to medical treatment or another disease.

Last reviewed: June 2015

Need more information?

These trusted information partners have more on this topic.

Found 2529 results

How your baby’s immune system develops

Learn how your baby's immune system develops and how breastfeeding and vaccinations help protect babies from serious illness.

Read more on Pregnancy, Birth & Baby website

General information about the immune system - Australasian Society of Clinical Immunology and Allergy (ASCIA)

The immune system is a complex network of cells and proteins that defends the body against infection.

Read more on ASCIA – Australasian Society of Clinical Immunology and Allergy website

Kids' Health - Topics - The immune system

Immunity (say im-yoon-it-i) means that you are protected against something. There are different kinds of immunity. This topic is about how different parts of our bodies work together to keep us from getting sick. Immunity to some diseases is passed on from our mothers before we are born. Immunisation (having your 'shots') helps our body's immune defence system protect us from diseases .

Read more on Women's and Children's Health Network website

Vaccination and antibodies - myDr.com.au

See how vaccines prepare your immune system to fight disease by taking advantage of the fact that the immune system can remember infectious organisms.

Read more on myDr website

Allergies - Lab Tests Online AU

Allergies (also known as hypersensitivities) are overreactions of the immune system to substances that do not cause reactions in most people. Hypersensitivities are grouped into four types - I, II, III and IV. These classifications are based on which parts of the immune system are activated and how long it takes for a reaction to occur.

Read more on Lab Tests Online website

Type 1 diabetes

Type 1 Diabetes Type 1 diabetes is an auto-immune condition in which the immune system is activated to destroy the cells in the pancreas which produce insulin

Read more on Diabetes Australia website

Type 1 diabetes

Type 1 diabetes is a condition where the pancreas does not produce insulin because the cells which make insulin have been destroyed by the immune system.

Read more on WA Health website

Immunoglobulins - Lab Tests Online AU

To detect and/or monitor increased or decreased levels of one or more of the immunoglobulin types (IgG, IgA, and IgM) that are used to evaluate a person's immune system status

Read more on Lab Tests Online website

What is a Clinical Immunology/Allergy Specialist - Australasian Society of Clinical Immunology and Allergy (ASCIA)

Clinical immunology/allergy specialists identify and treat the diseases that result from abnormalities of the immune system.

Read more on ASCIA – Australasian Society of Clinical Immunology and Allergy website

Growing Older with HIV

Information about the impact of HIV on our bodies and on the immune system as we get older.

Read more on AFAO – Australian Federation of AIDS Organisations website

Check your symptoms Find a health service

Healthdirect 24hr 7 days a week hotline

24 hour health advice and information you can count on

1800 022 222

Government Accredited with over 140 information partners

We are a government-funded service, providing quality, approved health information

Australian Government, health department logo ACT Government logo New South Wales government, health department logo Northen Territory Government logo Government of South Australia, health department logo Tasmanian government logo Government of Western Australia, health department logo
Feedback