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

2-minute read

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 (white blood cells; 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 and invade 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 microbe or to proteins from a microbe, so that your body is able to recognise and respond very quickly to any future exposure to the same microbe.

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 2017

Need more information?

These trusted information partners have more on this topic.

Top results

Acquired immune system information | myVMC

The acquired immune system's lymphocytes (T cells and B cells) attack antigens like bacteria and viruses, and create antibodies that prevent re-infection.

Read more on myVMC – Virtual Medical Centre website

Anatomy of the human immune system and lymphatic system | myVMC

The immune system has two parts: the acquired system (lymphocytes and antibodies that attack diseases), and the innate system (skin and other barriers).

Read more on myVMC – Virtual Medical Centre website

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

Innate immune system anatomy information | myVMC

The innate immune system includes skin and other barriers which prevent disease entering the body, and inflammatory and other responses which fight disease.

Read more on myVMC – Virtual Medical Centre 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

Allergic reactions and the immune system information | myVMC

Allergy is an exaggerated immune reaction to a usually harmless substance like pollen. Uncontrolled inflammatory and other allergic responses damage cells.

Read more on myVMC – Virtual Medical Centre 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

How does immunisation work? | Australian Government Department of Health

Vaccines stimulate the bodys natural defences to strengthen your immune system.

Read more on Department of Health 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

Healthdirect 24hr 7 days a week hotline

24 hour health advice 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 and advice

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