The Immune System: Your Natural Barrier Against Viruses and other Pathogens

Maintain your health by learning more about the immune system and how to keep it in optimal shape

A healthy immune system can keep you free from most bacterial and viral infections, will improve the healing of cuts and wounds, and will boost your energy levels. But a deficient immune system will constantly get you sick and can even be fatal.

Hence, it is important to learn the basics of how this system works and what you can do to boost and keep it in optimal condition.


The Basics

The immune system is a piece of complex machinery that involves organs, cells and proteins that work together to protect your body from pathogens and other potential threats. It is generally divided into two main sub-systems:


The innate immune system

Also called the nonspecific immune system, it provides the first stage of defence against an invading pathogen or particle. It is composed of physical barriers, such as the skin and the mucous membrane found in the surface of the digestive, respiratory, and genitourinary tracts. It also includes specific immune cells, like natural killer cells and phagocytes, which attack pathogens within hours of infection. Another property of the innate immune system is a lack of recognition or memory of an invading pathogen or particle: these cells just attack anything they deem dangerous. This system is also involved with the repair mechanism of cuts and wounds1.


Adaptive immune system

Also known as the acquired immune system, this system relies on the use of antibodies, also known as an immunoglobulin (Ig), specialised proteins that can recognise a pathogen that had previously entered the body. This allows for a highly specific and efficient response from adaptive immune cells, so they only destroy the invading pathogens and not our own cells2.


When an infectious agent, toxin or other foreign particle enters the body, both systems work together to destroy the pathogens or toxins. They also create the antibodies that will recognise these invading particles, if they ever enter the body again.

But, when it comes to pathogens, not all pathogens behave in the same and some are harder to destroy than others, like in the case of viruses.


Viral infections

Viruses are a unique type of infectious agent. Scientists can’t even agree on whether they are living organisms or not. However, their effects on the human body are well known and feared. Viral infections have killed millions of people over the past decades.

Like with bacteria or toxins, most viruses are recognised as pathogens and attacked by the immune system. However, some viruses have developed evasion strategies that allow them to persist undetected in the body and cause infection. There are also other factors that influence the strength and seriousness of a viral infection, such as how much of the virus entered the body and the point of entry (e.g. lungs, blood, or stomach).

In the case of coronaviruses, viruses like SARS-CoV and MERS-CoV (the viral agents causing SARS and MERS, respectively) have multiple strategies to avoid immune attacks. For example, both SARS-CoV and MERS-CoV can induce the production of special vesicles or sacs, where the virus can hide, undetected by immune cells. MERS-CoV has also been shown to inhibit the function of certain cells and genes that regulate immune function3.

So far, one recent study on SARS-CoV-2, the viral agent causing COVID-19, has identified potential mechanisms involving genetic mutations that may help the virus avoid attacks from the immune system. However, more research is needed to understand these evasion mechanisms, which one day will help design better ways to stop the spread of this disease.


Is your immune system in good shape?

Your health is in constant threat from outside pathogens, so It’s important to know if your immune system is working in optimal conditions, or if it needs a boost. Common signs of a compromised immune system include

  • Constantly getting a cold or infections
  • Regularly suffering from stomach problems
  • Slow wound healing
  • High levels of stress
  • Feeling tired all the time


Blood tests can detect the levels of certain immune cells in your body, like the antibodies igG, igM, and IgA, which are directly indicative of how well the immune system is working. If the levels of these antibodies are too high or too low, your immune system might need help.


Boosting your immune system

The immune system is composed of multiple organs and cells that work together to fight off infections. However, multiple factors can affect the function of this complex system, potentially leaving you with a sub-optimal defence against pathogens. The most studied and research-backed factors known to influence the functioning of the immune system include:

Sleep and circadian rhythms

Alterations to our normal sleep-wake pattern increase our risk of developing infectious diseases. During normal sleep, our body regulates the production of different hormones, which, in turn, influence the function of the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). Poor sleep can lead to overactivation of the SNS and HPA axis, which can lead to altered immune functions4.


Regular exercise

Leading an active lifestyle, either through regular intensive exercise or simply by maintaining an active lifestyle has multiple benefits in the body5. From an immunological perspective, regular exercise has a direct impact on the function of multiple immune cells6.



Following a balanced life-style has a positive influence on the immune system. Research has identified a complex interaction between the central nervous system (CNS), the endocrine system and the immune system. Stressors can activate the sympathetic–adrenal–medullary (SAM) axis and the HPA axis, causing the release of various hormones that affect immune function7.



Certain foods are rich in nutrients like vitamin A, folate, vitamin B12, zinc, copper, and selenium. These vitamins and minerals play important functions for the immune system. For example,

    • Vitamin A is important for the development of the immune system and is involved with cellular and humoral immune responses8.
    • Folate and Vitamin B12 are important micronutrients needed to produce nucleic acids and proteins. Deficiencies on these micronutrients can lead to dysfunction of immune cells, affecting multiple metabolic processes9.
    • Zinc is an important trace element required for the development and functioning of immune cells from both the innate and adaptive immune system10.


Multiple foods and supplements are available that can provide these and other important micronutrients. Botanicals are another important source of valuable compounds that help improve immune function. For more information see our article on Supercharging the HPA axis.




  1. Aristizábal B, González Á. Innate immune system. In: Anaya JM, Shoenfeld Y, Rojas-Villarraga A, et al., editors. Autoimmunity: From Bench to Bedside [Internet]. Bogota (Colombia): El Rosario University Press; 2013 Jul 18. Chapter 2. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459455/
  2. Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Chapter 24, The Adaptive Immune System. Available from:https://www.ncbi.nlm.nih.gov/books/NBK21070/
  3. Li X, Geng M, Peng Y, Meng L, Lu S. Molecular immune pathogenesis and diagnosis of COVID-19. Journal of Pharmaceutical Analysis. 2020 Mar 5. Read it!
  4. Irwin MR. Why sleep is important for health: a psychoneuroimmunology perspective. Annual review of psychology. 2015 Jan 3;66:143-72. Read it!
  5. Warburton DE, Bredin SS. Health benefits of physical activity: a systematic review of current systematic reviews. Current opinion in cardiology. 2017 Sep 1;32(5):541-56. Read it!
  6. Walsh NP, Gleeson M, Shephard RJ, Jeffrey MG, Woods A, Bishop NC, Fleshner M, Green C, Pedersen BK, Hoffman-Goetz L, Rogers CJ. Position Statement Part one: Immune function and exercise. Read it!
  7. Glaser R, Kiecolt-Glaser JK. Stress-induced immune dysfunction: implications for health. Nature Reviews Immunology. 2005 Mar;5(3):243-51. Read it!
  8. Huang Z, Liu Y, Qi G, Brand D, Zheng SG. Role of vitamin A in the immune system. Journal of clinical medicine. 2018 Sep;7(9):258. Read it!
  9. Mikkelsen K, Apostolopoulos V. Vitamin B12, Folic Acid, and the Immune System. In Nutrition and Immunity 2019 (pp. 103-114). Springer, Cham. Read it!
  10. Gammoh NZ, Rink L. Zinc and the Immune System. InNutrition and Immunity 2019 (pp. 127-158). Springer, Cham. Read it!