How The Immune System Works

What you need to know about the immune system: 

• The immune system is a complex network of organs, cells and tissues that helps protect the body from potentially harmful substances, germs and other threats.
• The immune system has two closely connected branches, the innate and adaptive immune systems. These two systems work together to recognise and respond to potential threats.
• Factors including nutrition, sleep, stress, physical activity, smoking, alcohol consumption and age can all influence immune function over time.
• Supporting immune health is often about consistent lifestyle habits, including a balanced diet, regular movement, adequate sleep and stress management.

Think of your immune system as your body's personal bodyguard, working around the clock to protect from potentially harmful substances, germs and other threats. It plays an important role in recognising what belongs in the body, responding to what doesn’t and supporting recovery1. 

It's your body's first line of defence, and it tends to thrive when you strike a balance of movement, mindfulness and nutrition in everyday life. There are plenty of ways to support the role of your immune system. But first, let's explore the role of the immune system, how it responds to potential threats and the factors that can influence immune function over time. 

What does the immune system do?

At its core, the immune system is an interconnected network of lymphoid organs, immune cells and signalling molecules. When immune activity is too low, the body may be more susceptible to infection. When immune activity becomes overactive or misdirected, it can contribute to allergic and autoimmune conditions² . 

When our immune system is exposed to pathogens such as bacteria, viruses or fungi, body cells try to engulf the pathogen to get rid of it³ . Some immune cells help identify and contain the threat, while others work to remove it and support recovery³. 

The function of the immune system also extends beyond responding to infection. It plays a role in repairing damaged tissues, removing old or abnormal cells, and helping the body maintain overall health and balance¹ ² .

Why immune system function matters

It’s easy to forget about protecting the immune system until you’re struck down by a pesky bug. That’s why it’s a good idea to see immune system health as something to care for on an ongoing basis, not just when you feel the first sniffle coming on. Look upon it as a two-way partnership: you take care of your immune system all year round, and your immune system will take care of you when it detects potential invaders¹ ² . 

How the immune system parts work together

The function of the immune system relies on a network of organs, tissues and specialised cells working together to identify and respond to potential threats. Understanding the different parts of the immune system can help explain how the function of the immune system supports everyday health³. 

Here's how the key players work: 

• White blood cells do much of the front-line work. Some cells, including neutrophils and macrophages, respond quickly to potential threats, while lymphocytes help the immune system adapt and develop a memory3. 
• Bone marrow is where many immune cells are produced. After early childhood, most of your immune cells are made here before they enter circulation throughout the body3.
• Lymph nodes are coordination hubs, where antigens from invaders are delivered, and the right immune cells are activated to respond3.
• The spleen helps filter the blood, remove pathogens and abnormal cells and support immune responses. It’s also a site where immune cells gather and coordinate their response2.
• The thymus is involved in the development and maturation of T cells, helping the body to distinguish between its own tissues and potential threats3.
• Skin and mucous membranes act as important physical and chemical barriers. The skin helps prevent germs from entering, while substances like enzymes in tears and stomach acid help neutralise potential threats before they can cause harm3.

Once mature, immune cells move throughout the body and populate lymph nodes, the spleen, tonsils and other lymphoid tissues, allowing them to respond wherever they are needed.² 

Innate vs adaptive immune system

The immune system has two closely connected branches: the innate immune system and the adaptive immune system. While they have different roles, they work together whenever the body responds to a potential threat¹. 

Innate immune response

The innate immune system provides the body's immediate response to potential threats, which is why it's often referred to as the non-specific immune response. It includes physical barriers such as the skin and mucous membranes, along with immune cells, including natural killer cells and phagocytes¹.

The role of the innate immune system is to recognise and respond quickly to a wide range of germs and other potentially harmful substances. As the body's first line of defence, it helps limit the spread of threats while activating other parts of the immune system when needed¹.

Adaptive immune response

The adaptive immune system provides a more targeted response. After exposure to a specific germ, it can produce antibodies and activate specialised immune cells that recognise and respond to that particular threat¹.

Because the adaptive immune system can develop immunological memory, it is able to respond more efficiently if the same germ is encountered again in the future. This is why it is sometimes referred to as the acquired immune system¹.

What can influence a weak immune system?

There are a range of different factors that can influence immune function over time. Some of these factors are outside your control, while others are linked to everyday habits and lifestyle choices. 

• Nutrient intake. The immune system relies on a range of micronutrients, including vitamins A, C, D, E, B6 and B12, folate, zinc, iron, copper and selenium. These nutrients support different aspects of immune function, with even small deficiencies affecting immunity6.
• Sleep. Sleep plays an immune-supportive role, and ongoing sleep deprivation has been linked with changes to both innate and adaptive immune function7.
• Stress. Short bursts of stress can briefly sharpen immunity, but chronic stress tends to do the opposite, raising cortisol over time, which can affect the body’s ability to respond to threats8.
• Smoking and alcohol. Smoking has been shown to affect both innate and adaptive immune responses⁹. Long-term heavy alcohol consumption has also been associated with impaired immune function and an increased susceptibility to infection¹⁰. 
• Physical activity. Regular physical activity is associated with better immune health and may help support the normal movement and activity of immune cells throughout the body.¹¹ 
• Age and life stage. Immune function naturally shifts with age, partly as the thymus becomes less active and low-grade inflammation gradually increases12.

How to support your immune system

Giving your immune system a little TLC can go a long way towards supporting its function, especially during cold and flu season. Alongside immune-supporting lifestyle choices - getting enough sleep, managing stress, looking after your gut, keeping active, and nourishing your body with a varied, well-balanced diet - you may also wish to consider a few vitamins, minerals and herbs traditionally associated with immune support:

• Echinacea. A long-standing favourite, echinacea has been traditionally used in Western herbal medicine to support immune system health and to help relieve the symptoms of mild upper respiratory tract infections.
• Vitamin C. An antioxidant that helps reduce free radicals formed in the body, vitamin C also supports overall immune system health and function.
• Zinc. A key immune mineral, zinc helps support immune system function — and because zinc deficiency is relatively common, it's a nutrient worth being mindful of.
• Vitamin D. Often called the "sunshine vitamin," vitamin D is both a nutrient we eat and one our bodies make through sunlight exposure. It plays a role in immune health — and notably, a sizeable proportion of Australians don't get enough.

If you have specific concerns about your immune health, it's always worth speaking with your healthcare professional or pharmacist. 

Looking to learn more? Explore the Swisse Wellness Hub for articles like the link between sleep and immune health and a dietitian’s guide to immunity boosting foods. 

References:

1. NCBI. (2023). How does the immune system work? [online] National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/books/NBK279364/
2. Parkin, J., & Cohen, B. (2001). An overview of the immune system. The Lancet, 357(9270), 1777–1789. https://doi.org/10.1016/S0140-6736(00)04904-7
3. Nicholson, L. B. (2016). The immune system. Essays in Biochemistry, 60(3), 275–301. https://doi.org/10.1042/EBC20160017
4. Randolph, G. J., Ivanov, S., Zinselmeyer, B. H., & Scallan, J. P. (2017). The lymphatic system: Integral roles in immunity. Annual Review of Immunology, 35, 31–52. https://doi.org/10.1146/annurev-immunol-041015-055354
5. Lewis, S. M., Williams, A., & Bhatt, D. L. (2019). Structure and function of the immune system in the spleen. Science Immunology, 4(33), eaau6085. https://doi.org/10.1126/sciimmunol.aau6085
6. Gombart, A. F., Pierre, A., & Maggini, S. (2020). A review of micronutrients and the immune system — working in harmony to reduce the risk of infection. Nutrients, 12(1), 236. https://doi.org/10.3390/nu12010236
7. Garbarino, S., Lanteri, P., Bragazzi, N. L., Magnavita, N., & Scoditti, E. (2021). Role of sleep deprivation in immune-related disease risk and outcomes. Communications Biology, 4, 1304. https://doi.org/10.1038/s42003-021-02825-4
8. Shitu, S., Abdu, F., Tadesse, H., Bante, A., Seifu, B., & Kassa, B. (2024). Immunology of stress: a review article. Journal of Clinical Medicine, 13(21), 6394. https://doi.org/10.3390/jcm13216394
9. Qiu, F., Liang, C-L., Liu, H., Zeng, Y-Q., Hou, S., Huang, S., Lai, X., & Dai, Z. (2017). Impacts of cigarette smoking on immune responsiveness: Up and down or upside down? Oncotarget, 8(1), 268–284. https://doi.org/10.18632/oncotarget.13613
10. Szabo, G., & Saha, B. (2015). Alcohol's contribution to compromised immunity. Alcohol Research: Current Reviews, 37(2), 159–170. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6826800/
11. Nieman, D. C., & Wentz, L. M. (2019). The compelling link between physical activity and the body's defense system. Journal of Sport and Health Science, 8(3), 201–217. https://doi.org/10.1016/j.jshs.2018.09.009
12. Goyani, P., Christodoulou, R., & Vassiliou, E. (2024). Immunosenescence: Aging and immune system decline. Vaccines, 12(12), 1314. https://doi.org/10.3390/vaccines12121314