• The immune system, your personal bodyguard

The immune system, your personal bodyguard

By Eliana Bazac

We all think we know what the immune system is. The term is actually self-explanatory and it has most likely been overused lately by numerous people in all walks of life.

The coronavirus outbreak has led to the recirculation of very many myths previously used in the case of other conditions, as a means to help stem the infection. From eating garlic to dosing up on vitamin C or drinking cow’s urine – the social media has been abundant in ‘advice’ to help ‘boost’ your immune system and keep you safe. The World Health Organisation (WHO) and other health organisations around the world have been working hard lately responding to misinformation and rumours on social media.

So, let’s explore the topic of immunology, find out how the immune system works and if there is anything we can do to help it defend us against pathogens.

Some definitions to get us going

The immune system is a complex defence mechanism protecting the body from the attack of viruses, bacteria, fungi, parasites and other pathogens[1].

Leukocytes are a type of blood cells that are produced in the bone marrow and the lymph tissue. Also called white blood cells, leukocytes can be further categorised into granulocytes (neutrophils, eosinophils, and basophils), monocytes, and lymphocytes (T cells and B cells)[2]. Neutrophils and monocytes are phagocytic, namely they remove pathogens by ingesting them[3].

An antigen is a substance that is capable of stimulating an immune response, specifically activating lymphocytes. An antigen can be a bacterium, fungus, virus, toxin or even a faulty or dead cell[4].

The study of the immune system is known as immunology which is a branch of the medical and biology sciences. The terms of ‘immunology’ was coined by Élie Metchnikoff, a Russian zoologist, known for his pioneering work in this field.

Short history of immunology

The ancient world

The earliest mention of the concept of ‘immunity’ comes from the Athenian historian and general, Thucydides, c. 460 – c.  400 BC. In 430 BC, during the second year of the Peloponnesian War, Athens was devastated by a plague that killed an estimated 75,000 to 100,000 people. Thucydides noted that people who had recovered from a previous bout of the disease could look after the sick without themselves becoming sick a second time[5].

[2.51.6] Yet it was with those who had recovered from the disease that the sick and the dying found most compassion. These knew what it was from experience, and had now no fear for themselves; for the same man was never attacked twice- never at least fatally. And such persons not only received the congratulations of others, but themselves also, in the elation of the moment, half entertained the vain hope that they were for the future safe from any disease whatsoever’[6].

Early Middle Ages

In the 10th century AD, Persian physician Rhazes was the first one to distinguish between smallpox and measles by providing an accurate description of each one. Also for the first time in history, Rhazes put forth the theory of acquired immunity. He noted that people who survived and recovered from a bout of smallpox wound never get it again[7].

18th century

The work of English physician Edward Jenner paved the way to the discovery of a vaccine against smallpox. Looking into the practice of inoculation as a means to immunise against smallpox, Jenner demonstrated that an infection with the relatively mild cowpox virus conferred immunity against the deadly smallpox virus[8].

The practice was already used in China, India, Circassia and West Africa. Inoculation consisted of the deliberate introduction of material from smallpox pustules into the skin. The practice generally resulted in a less severe reaction which induced immunity to smallpox[9].

19th century

French biologist, microbiologist and chemist Louis Pasteur put forward what is now known as the germ theory of disease. Through his research, he demonstrated that microorganisms cause disease which results in an immune response within the body[10]. Pasteur’s incredible breakthroughs in the discovery of the first vaccines for fowl cholera, anthrax, and rabies have helped save many lives since.

In the 19th century, immunology made rapid progress through the astounding work of Robert Koch and Paul Ehrlich who were both awarded a Nobel Prize for their discoveries.[5]

20th century

In 1901, US Army physician Walter Reed demonstrated that viruses were human pathogens, through the discovery of the yellow fever virus.[5]

How does the immune system work?

The immune system relies on a layered defence mechanism, i.e. innate, adaptive and passive immunity. Physical barriers such as the skin prevent pathogens from entering the body. If the physical barrier is breached, the innate immune system which is composed on leukocytes will spring into action. The response is non-specific and as part of the process, leukocytes will identify and destroy pathogens through contact or by ingesting them – phagocytes.[5]

The adaptive immune system is composed of antigens, B cells and T cells and generates a pathogen and antigen specific response. This allows for a more powerful immune response through which each pathogen will be tackled by a specific antibody.[5] Antibodies are specialised proteins produced by B cells which lock on specific antigens, a process with confers the body immunity against the same type of pathogen. T cells then destroy antigens marked by the antibodies by releasing cytotoxins.[11] These agents penetrate the target cell’s membrane and induce apoptosis or programmed cell death.[5]

Passive immunity is developed after antibodies are received from another person. For instance, babies receive antibodies through the placenta from the mother. After they are born, large quantities of antibodies are contained in the mother’s breast milk.

What is the immune system’s response to COVID-19?

When the virus enters the body, it will initially infect a few cells. These cells will be stopped from doing what they normally do and will be reprogrammed to replicate the virus. The virus will then go on to infect other healthy cells. The innate immune system will be activated early on in the process, but the response will be non-virus specific. This activation will give rise to a number of symptoms such as headaches, fever, and muscular pain. At this point, the innate immune system’s purpose is to keep the body alive until the adaptive immune system is activated.

The adaptive immune system springs into action at a later stage. The reason is because this is a new type of virus that it has never met before. Therefore it needs time to create specific antibodies – which happens within 2 to 3 weeks. Normally, when the adaptive immune system becomes active, the innate system stands down. It has been noticed however that in certain patients this does not happen. The innate system continues its activity which may then result in progressive inflammation and wide damage to uninfected tissue. This is difficult to manage clinically and may result in the patient’s death. It is assumed that people with comorbidities die as a result of the additional stress caused by the viral infection and exacerbated reaction of the innate immune system[11].

Can I keep the immune system balanced and healthy through diet?

We have kept away from using the phrase ‘boosting the immune system’. The immune system is so complex, it is very difficult to affirm it can be boosted by any single action. The aim should be to try and keep your immune system balanced and healthy instead, through a healthy diet and lifestyle.

Although further research is required in the case of COVID-19, a range of nutrients found in certain foods might help the immune system in fighting influenza or the common cold. Moreover, certain foods may help decrease low-grade inflammation linked to underlying health conditions, such as cardiovascular disease or diabetes[12]. This is particularly important as certain COVID-19 patients may manifest a severe inflammation response which contributes to lung failure and death.[11]

Nutrients that may help the immune response include vitamins A, C, D, E, B-6, folate, iron, zinc and selenium. Certain promising effects may be associated to the intake of whole foods such as turmeric, green tea, goji berry and broccoli.[12]

A healthy diet should include citrus fruits, berries, broccoli, spinach, mushrooms, red bell peppers, sweet potatoes, shellfish, beans, almonds, hazelnuts, peanut butter, turmeric and tea. These foods may be beneficial especially in the case of elderly individuals who most often than not miss out on the nutrients that they offer[12]

It is equally important to drink in moderation, not smoke, get enough sleep, minimise stress and exercise regularly[13].


1. https://www.medicalnewstoday.com/articles/320101

2. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/leukocyte

3. https://en.wikipedia.org/wiki/Phagocytosis

4. [https://www.britannica.com/science/antigen

5. https://en.wikipedia.org/wiki/Immune_system

6. https://www.livius.org/sources/content/thucydides-historian/the-plague/

7. https://library.uab.edu/locations/reynolds/collections/medical-greats/rhazes-al-razi

8. https://en.wikipedia.org/wiki/Smallpox_vaccine

9. https://en.wikipedia.org/wiki/Inoculation

10. https://www.sciencehistory.org/historical-profile/louis-pasteur

11. https://www.sciencemediacentre.org/expert-reaction-to-questions-about-covid-19-and-viral-load/

12. https://edition.cnn.com/2020/03/27/opinions/healthy-diet-immune-system-covid-19-mozaffarian-glickman-nikbin-meydani/index.html

13. https://www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system

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