The Biological Marvel of The Human Immune System

The human immune system works to not only heal your body when it is exposed to a pathogen, but also protect it from pathogens you have already been exposed to.
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Medically Reviewed by Dr. Sophie Pollon-MacLeod, ND

The human immune system works to not only heal your body when it is exposed to a pathogen, but also protect it from pathogens you have already been exposed to. It is divided into two parts: the innate and adaptive immune system. You are born with the former, while the latter is acquired through exposure to specific pathogens. Both systems are influenced by a series of factors that need to be taken into consideration when discussing optimal immune function.

How Does The Human Immune System Work?

The human immune system is a remarkable network of organs, glands, defense cells, proteins and chemicals that work in concert to protect and heal your body when it is exposed to a pathogen (bacteria, viruses, fungi) or a toxin (heavy metals and pesticides). There are two main parts of the immune system: innate (nonspecific) immunity and adaptive (specific) immunity. You are born with the former, while the latter is acquired and maintained over the course of your lifetime. Both parts of the immune system are equally important and work together when fighting off an outside invader like a virus, but they are both influenced by a variety of lifestyle factors that many do not take into consideration when they think about optimal immune function.

Because immunity is one of the most widely discussed and debated topics amidst the global pandemic, it is important to take a step back and critically look at the actual science of immunity and the data accompanying it in the context of SARS-CoV-2 (COVID-19).


What Is The Difference Between Innate and Adaptive Immunity?

Innate Immunity

Your innate or nonspecific immunity is inherited from your mother and becomes active the minute you are born. It is a mix of surveillance and first response; think of it as high-tech security meets a team of first responders. This team is comprised of highly specialized white blood cells (leukocytes) that not only seek out, capture and destroy invaders, but also cancerous cells. If the skin and mucosal membranes (barrier immunity aka external innate immunity) are unsuccessful at keeping out an invader, internal innate immunity kicks in. This process is known as phagocytosis, where neutrophils and macrophages literally devour pathogens, while natural killer cells cause virus-infected or cancerous cells to self-destruct via a process known as apoptosis. Furthermore, a remarkable substance called interferon is released from virus-infected cells. This highly specialized group of proteins warn other cells to produce virus-blocking enzymes that inhibit viral replication within the cell.

This is also where the “fire” cavalry is called in with the activation of mast cells and other components of inflammation, as seen with swelling and fever, where the body rapidly heats up in an attempt to kill off the invading pathogens. In most cases, our innate immunity is very successful at eating and burning up a variety of pathogens, which is seen with the healing of broken skin for example. This action is rapid, but weaker compared to that of adaptive immunity, which is slower to respond, but much stronger once it kicks into gear.


Adaptive Immunity

Your adaptive or specific immunity is something you acquire and maintain throughout the course of your life. It is the part of the immune response that adapts based on the type of threat it is exposed to. Think of it as a team of elite ninjas with millions of throwing stars (antibodies) that are not only uber stealthy, but are apex nerds because they love to collect and store data while engaged in lethal combat. The adaptive immune system involves two types of responses: antibody-mediated or cell-mediated. The former involves B lymphocytes (B cells) creating special proteins called antibodies. The latter involves an array of cell-to-cell communication between immune cells and direct or indirect death of infected cells.

There are approximately two trillion lymphocytes in the human body that are constantly circulating throughout fluids and tissues covertly patrolling in search of potential invaders. Now here is where things get interesting. The surface of each pathogen’s cell membrane has a unique structure comprised of antigens, which are large, foreign signalling molecules that are the key to a full and effective immune response. In the case of COVID-19, its spike protein is also its antigen.

Let’s say a virus is able to escape our superteam of first responders, so it’s free-floating in the bloodstream trying to find tissue cells it can invade, shut down and use to replicate itself. Because our little ninjas are on constant patrol with the objective of seeking out, binding to and tagging pathogens, the virus is eventually found by the B cells, which then go into full combat mode. Upon binding of the antigen to its specific antibody, B cells begin to rapidly replicate into identical cells with the exact antibodies for the specific antigen of said virus.

Whilst replicating, the B cells differentiate into two specific types: effector cells and memory cells. The former are power plants that produce a plethora of antibodies. The latter are the nerdy data collectors that memorize the genetic code of the specific antibody and store it away in the event you are exposed to the same virus or pathogen again. This is known as naturally acquired immunity, because if you are exposed to the identical virus or pathogen again, your body has the exact antibodies to fight it off with even more power and speed.

Although the B cell response is very powerful, viruses and other pathogens can evade it and successfully hijack a cell and begin replicating. Unfortunately, antibodies cannot penetrate a cell membrane, so this is where the cell-mediated response comes into play. T cells are actually a group of cells that each have a specific function, wherein helper T and killer T cells are quite active and abundant.

The process of B cells coming into action with their antibodies catches the attention of helper T cells, who then begin rapidly replicating and sound the alarm to other lethal immune cells through the production of cytokines. As a result, helper T cells regulate the entire adaptive immune response. They are also responsible for the proper functioning of all immune cells; thus, critical for a balanced, optimally functioning immune system by ensuring effective communication between innate and adaptive immunity. Killer T cells on the other hand do what their name states. They initiate cell death directly by puncturing the cell wall of infected cells or indirectly by excreting chemicals that cause apoptosis in infected cells.

Although the immune system in its entirety is a true biological marvel with a hyperintelligent adaptive response, it is limited in that the first exposure of a disease pathogen is less potent than that of a second exposure and so on. This is where the logic and power of vaccines take effect. By giving your body a specific disease antigen artificially, your B cells will create antibodies for a disease it has yet to naturally become exposed to. In the event you do contract it, the severity of disease will be much less pronounced. This also speaks to the logic of the multi-dose approach to COVID-19 vaccines. Two doses are the equivalent of two natural exposures; thus, a third exposure via contraction of the active virus creates a response that is three times the strength of what your body produces on its own during initial exposure.


Intelligent Immune Strategies—Regulating Not Boosting Immunity

Although vaccines are one of the most significant breakthroughs in modern medicine and are recommended to everyone who is eligible, they only account for one aspect of an intelligent immune strategy when dealing with something as complex as COVID-19. The other aspect is ensuring that your immune system actually works correctly, which requires serious effort for the majority of us. It not only has to be maintained, but also regulated in order to function optimally. Like many other diseases, the host immune system determines the progress of COVID-19 and fatality.1

Think of it as if you are a captain meets sensei. Your tiny powerhouse crew of first responders and ninjas cannot deal with an emergency or go into battle without sufficient training, nutrition and tools. Because they are under your direction and care, it is your responsibility to provide them with the conditions and nourishment necessary in order for them to be fit for their extremely difficult functions. How can your ninjas scale walls and kick pathogenic butt if they are undernourished, dehydrated, out of shape and sleep-deprived? They can’t, so it is your responsibility to ensure all of their needs are met!

So how does one do this exactly? Well, the answer is quite simple, seeing it is all about lifestyle. There are 5 basic tenets that are crucial for optimal immune function: sufficient sleep and exercise, effective stress reduction, hydration and a nutrient-rich diet. There is a reason these topics are consistently discussed within our articles and immunity is no exception.


Everyone is different, but the average adult requires approximately 6-8 hours of deep, restorative sleep per night. Indeed, this is easier said than done for many, but research has confirmed that sleep deprivation reduces natural killer cell activity and protective cytokines. Moreover, it has been shown that less than 5 hours of sleep increased the risk of a cold by 350% compared to more than 7 hours of sleep. Lack of sleep also increases cortisol, which acts as an immune suppressor at high levels, disturbing the microbiome, which is directly tied to immune responses. The normal gut microbiota can maintain immune response to a viral infection and improve respiratory symptoms.2 Be sure to get your Zs!



Regular exercise in the light-to-moderate category not only has a profound effect on your hormones, blood sugar and subsequent mood, but also encourages a diverse, healthy microbiome, which we know is critical to immune function. Furthermore, regular exercise of this kind also has an anti-inflammatory effect, which is critical in the context of COVID-19, seeing as it has a significant pro-inflammatory effect.


Stress Management

Although effective stress management seems to be eluding the masses presently, it is so critical to our immune function and mental health status. Deep breathing, yoga, meditation and mindfulness are simple, but effective strategies for stress reduction. Just ten slow, deep breaths can effectively reduce stress by lowering cortisol and heart rate; thus, regulating your nervous system, positively impacting your microbiome, hormone and cardiovascular status, which all tie into immune function. Do your best to avoid stressors where possible, reduce news and social media consumption and carve out a minimum of 30 minutes a day to do something that brings you joy. To learn more about the stress response, mood and gut function, check out our article on the gut-brain axis.


Even though research is scarce on the impacts of sufficient hydration on immunity, its critical role in immune function cannot be understated. Simply put, we are made up of approximately 60% water. Humans are little oceans for all intents and purposes, which is why we die much faster from dehydration than starvation. Water makes up about 90% of both blood and lymph, which are both involved in immune responses. In short, when there is less water, there is less volume of the fluids that are responsible for carrying immune cells, nutrients and signals to where they need to go and toxins and debris out of the body. Researchers are in continuous debate about how much water a person actually needs and what constitutes an appropriate water source, but here are some logical basics.

Carry a reusable water bottle with you and sip throughout the day. Don’t just drink when you are thirsty and avoid chugging. Aim for approximately two litres of filtered water per day and increase after exercise and heat exposure. Limit coffee to one cup per day because excess caffeine will increase cortisol levels. If you require a pick-me-up, choose green tea, as it has a gentler effect on the nervous and endocrine systems. Plus, it is packed with nutrients that play a helpful role in immunity. You can also follow Fullscript’s simple guideline on hydration below.


No matter what way you slice it, you are what you eat; therefore, if your diet is lacking in dense nutrition, then so are your cells, organs and your immune system. Remember, your little first responders and ninjas need super nutrition in order to support their super responsibilities, so if you are feeding them junk, then their performance will reflect that. However, if you take the time to eat a whole food, plant-based or plant-rich diet, full of fermented food and resistant starch you are giving your whole body and your little team of superheroes exactly what is needed to perform with excellence. Moreover, these dietary patterns are packed with phytochemicals such as flavonoids and other micronutrients with high antioxidant activity that play critical roles in overall immune function. Nutritional factors play a key role in both innate and adaptive immunity. Obesity, type 2 diabetes, atherosclerotic cardiovascular disease, and hypertension are risk factors for severe COVID-19. The aetiology of these conditions is largely driven by poor nutrition and unfavourable lifestyle choices.3 Indeed, making the above dietary choices are easier said than done for many; however, even small, gradual changes can have big impacts. Start by adding in something nutritious every few days, and slowly cut back on the rest.


Pro Tips for Immunity


Drink passionflower, holy basil & melissa tea to wind down
Cut off devices a minimum of an hour before bed
Sleep in a dark, cool room with a weighted blanket


Take epsom salt baths
Diffuse or inhale on blends like Chill Out or Stress Relief by Saje
Deep breathing & EFT tapping system


Walk, dance, sing and shake it out daily!
Tai chi, yoga, pilates, rebounding, & skipping 3 x/week
Enjoy healthy, safe sexual activity


Invest in a good water filter
Carry a reusable water bottle with you
Add citrus, cucumber & herbs to jazz things up


Eat a large bowl of dark salad greens or steamed greens daily
Add berries, citrus fruits, beans, nuts, seeds & whole grains daily
Eat anti-inflammatory foods like turmeric & ginger root

Cut Out/Avoid

Sugar/Highly Processed Foods


The Role of NHPs in Immune Regulation

Since the inception of the pandemic, there has been a surge of research on therapeutic nutrition and botanical medicine as potential preventions and treatments of COVID-19. As a result, there have been a lot of misleading claims around certain NHPs as “cures” for COVID-19. That said, there are a multitude of studies underway on nutrients like vitamin C, vitamin D, zinc, quercetin and other flavonoids that are promising. However, before you pump your system full of them, you need to understand their role in the context of immunity and their actual status regarding COVID-19 research to ensure you make a truly informed decision.


Vitamin C

Vitamin C aka the “miracle vitamin” was given this name by Dr. Linus Pauling for good reason. This water-soluble vitamin not only has powerful antioxidant and anti-inflammatory properties, but on top of its role in supporting joint, bone and skin health, hormone synthesis, and detoxification, it is critical for ensuring proper immune function. Vitamin C accumulates in leukocytes, in concentrations of 50−100-fold higher than in the plasma. During infection, vitamin C that is present in leukocytes is rapidly utilized.4 Interestingly, low levels of vitamin C are found in patients with ARDS (acute respiratory distress syndrome), sepsis, pneumonia and other viral infections. What’s more, Vitamin C targets interleukin 6 (IL-6), which appears to drive the often fatal cytokine storm seen in severe COVID-19. Clinical studies have demonstrated that intake of 1 g/day of vitamin C increases IL-10 secretion by peripheral blood mononuclear cells. IL-10 works as a negative feedback mechanism with IL-6 and controls inflammation.4 1000-3000 mg per day is a good range due to its safety profile at higher doses. You can learn more about vitamin C here.

Vitamin D

Vitamin D’s role in immunity and the prevention of severe respiratory illness is very well established; therefore, it is not surprising that it is one of the most studied nutrients in COVID-19. Vitamin D promotes the differentiation of monocytes to macrophages whilst increasing superoxide production, phagocytosis and bacterial destruction.4 It also modulates the adaptive immune system by decreasing pro-inflammatory cytokines. It is noteworthy that many COVID-19 patients with severe illness are vitamin D deficient wherein deficiency is linked to comorbidities such as hypertension, diabetes and obesity, which are all risk factors for more severe illness. Conversely, a recent study concluded that above normal blood levels of vitamin D have no impact on prevention or severity of COVID-19. That said, those who live in northern climates above 35 degrees latitude tend to be deficient during winter months; thus, it is critical to ensure sufficient levels are maintained. Because vitamin D is fat-soluble, more does not always mean better. Unless you have your levels checked and you are being monitored by a physician, stick to 1000-2500 IU per day. You can learn more about vitamin D here.

@ottawa_naturopath New Health Canada update to prescription drug list for the dose of Vitamin D. Link in my bio #vitamind #naturopathicdoctor #healthcanadaapproved ♬ original sound - Sophie Pollon-Macleod

Zinc is another heavy hitter when it comes to proper immune function, which is why it is also extensively being studied in relation to COVID-19. Zinc maintains the thymus gland, where T cells mature and differentiate. Zinc has the dual action of both anti-oxidant and anti-inflammatory as seen in its ability to scavenge free radicals and reduce inflammatory cytokine IL-6 while stimulating anti-inflammatory cytokine IL-10. Furthermore, it synthesizes interferon which COVID-19 appears to inhibit, which certainly explains why it has such a high viral load. Zn not only plays an important role in IL-2 and IFN-γ production, but also stimulates macrophages to produce IL-12. IL-12 activates the natural killer cells and T cytotoxic cells. Both IFN-γ and IL-12 play a crucial role in destruction of various pathogens.1 Like vitamin D, more is not always better. The daily recommended amount of zinc is 8 mg for females and 11 mg for males. That said, it needs to be taken in a proper ratio to copper, because of the codependent relationship these two minerals have. If taken separately long-term, one will deplete the other, which is why taking a stand-alone Zinc at 50 mg per day is not recommended unless being monitored by a physician. You can learn more about a balanced zinc and copper formula here.


Quercetin, Hesperidin and Naringin

These polyphenols are regularly discussed due to their profound impact on the microbiome, but they also have other incredible properties which make them diverse therapeutic agents. Flavonoids possess significant anti-bacterial, anti-oxidant, anti-cancer, anti-inflammatory, and immunomodulatory abilities. In addition, flavonoids exert a strong anti-viral capacity in numerous pathologies.2 Quercetin has been long recognized for its powerful anti-inflammatory effects as seen with its long-standing use as a natural antihistamine, while hesperidin and naringin have been shown to modulate inflammation and feed healthy gut bacteria.

These combined effects have made them points of interest in COVID-19 research. With respect to quercetin, although the preliminary results are promising in terms of shortening duration and severity of illness, more controlled studies with larger sample sizes are needed to truly confirm its efficacy as a therapeutic agent regarding COVID-19. That said, along with EGCG (green tea), quercetin is a known ionophore of zinc. Simply put, ionophores effectively transport certain molecules across cell membranes, in turn helping them do their jobs more effectively. 500 mg per day of flavonoids is a great place to start as an extra layer of support to your immune system. You can learn more about quercetin here and hesperidin and naringin here.

The value of these nutritional substances cannot be understated; however, they are not a magic bullet against COVID-19, regardless of what you may read. They in no way replace vaccines, hygiene and public health measures like social distancing and masks. That said, taking steps to regulate your immune system with the 5 basic tenets and focusing on foods rich in these nutrients, along with responsible supplementation will increase the odds of keeping severe illness, its long-term effects and fatality at bay.


Getting Started

The above recommendations are excellent starting points to regulate your immune system, but if you need some guidance, consider working with one of our registered holistic nutritionists to get your diet cleaned up and gut reset. If you are ready to take your health to the next level, consider booking in with one of our team of experts for microbiome mapping, hormone balancing and IV therapy.

*This article is not intended to represent medical advice. Please contact a qualified health practitioner if you want to use any natural health products for specific health conditions. Furthermore, please note that the terms “female” and “male” are strictly used to represent biology and in no way reflect one’s gender identity or expression.


Pal, Amit, et al. “Zinc and Covid-19: Basis of Current Clinical Trials.” Biological Trace Element Research, Springer US, Aug. 2021,

Liskova, Alena, et al. “Flavonoids against THE Sars-Cov-2 Induced Inflammatory Storm.” Biomedicine & Pharmacotherapy, Elsevier Masson, 25 Feb. 2021,

Kim, Hyunju, et al. “Plant-Based Diets, Pescatarian Diets and COVID-19 Severity: A Population-Based Case–Control Study in Six Countries.” BMJ Nutrition, Prevention & Health, BMJ Specialist Journals, 1 June 2021,

Shakoor, Hira, et al. “Immune-Boosting Role of Vitamins D, C, E, Zinc, Selenium and Omega-3 Fatty Acids: Could They Help against COVID-19?” Maturitas, U.S. National Library of Medicine, 9 Aug. 2020,

Lykkesfeldt, Jens, and Pernille Tveden-Nyborg. “The Pharmacokinetics of Vitamin C.” Nutrients, MDPI, 9 Oct. 2019,

Bizzaro, Giorgia, et al. “Vitamin D and Autoimmune Diseases: Is Vitamin D Receptor (VDR) Polymorphism the Culprit?” The Israel Medical Association Journal: IMAJ, U.S. National Library of Medicine, 17 July 2017,

da Luz Scheffer, Débora, and Alexandra Latini. “Exercise-Induced Immune System Response: Anti-Inflammatory Status on Peripheral and Central Organs.” Biochimica Et Biophysica Acta. Molecular Basis of Disease, Elsevier B.V., 1 Oct. 2020,

Ticinesi, Andrea, et al. “Exercise and Immune System as Modulators of Intestinal Microbiome: Implications for the Gut-Muscle Axis Hypothesis.” Exercise Immunology Review, U.S. National Library of Medicine, 2019,

Sallis, Robert, et al. “Physical Inactivity Is Associated with a Higher Risk for Severe COVID-19 Outcomes: A Study in 48 440 Adult Patients.” British Journal of Sports Medicine, BMJ Publishing Group Ltd and British Association of

Sport and Exercise Medicine, 8 Apr. 2021,

Di Pierro, Francesco, et al. “Possible Therapeutic Effects of Adjuvant Quercetin Supplementation against Early-Stage COVID-19 Infection: A Prospective, Randomized, Controlled, and Open-Label Study.” International Journal of

General Medicine, U.S. National Library of Medicine, 8 June 2021,

Derosa, Giuseppe, et al. “A Role for Quercetin in Coronavirus Disease 2019 (Covid-19).” Phytotherapy Research: PTR, John Wiley & Sons, Ltd., Mar. 2021,

Bartholomew, Rachel. “Why Is Hydration Important for Your Immune System?” Nutri Advanced, 12 Aug. 2020,

Sherwood, Lauralee. Human Physiology: From Cells to Systems. Australia: Thomson Brooks/Cole, 2004. Print.

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Naturopathic Doctor Sophie-Pollon-MacLeod
Dr. Sophie Pollon-MacLeod, B.Sc., N.D.

Dr. Sophie is a Naturopathic Doctor and Sports Nutritionist with a passion for evidence-based approaches to supporting her patient’s health. Prior to obtaining her doctorate in Naturopathic Medicine, Dr. Sophie completed her undergraduate degree in Human Kinetics at the University of Guelph. She is also a personal trainer with over 8 years of experience.

Her experience as a trainer ignited her passion to pursue a career in healthcare and help others towards feeling their best. Dr. Sophie combines her expertise in exercise physiology and naturopathic medicine to support her patients towards achieving weight loss, improving performance and aiding in pain management. She goes beyond symptom management and utilizes a full-body approach to get to the root of health concerns. Dr. Sophie possesses additional qualifications from the International Society of Sports Nutrition (ISSN) and Functional Range Conditioning (FRC®).