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How Does the Immune System Work?

Most of us probably do not think much about our immune system, unless we are fighting an illness or in the midst of a pandemic. One good thing to come from the COVID-19 pandemic is a greater awareness of the importance of maintaining a healthy immune system and taking measures to prevent the spread of germs.

Since overall health is vital to a strong immune system, we recently explained the importance of maintaining the 5 Pillars of Health. We discussed the importance of each pillar: sleep, exercise or activity, nutrition, stress management, and relational or emotional health. We also reviewed specific things you can do to strengthen each one. You can read all about it in this post.

In addition to the five pillars of health, there are five goals we can target to strengthen specific components of the immune system. In order to understand the significance of each goal, it helps to have a basic understanding of how the immune system works. So, here is a very simple overview of how a healthy immune system should work and goals to strengthen it.

Immune System

Reasons We Become Ill

There are two major factors in your likelihood of becoming ill after exposure to a pathogen. The first is your level of health and the strength of your immune system. This makes sense if you consider that immune-compromised, elderly, and very young people are usually most at risk during an outbreak.

The second factor is the dose you are exposed to. Simply being in the same room as an ill family member brings a lower risk than if your child repeatedly sneezes or coughs right in your face. This is why health care workers can become seriously ill and even die during a viral outbreak. They are exposed to the virus in such high quantities that their normally healthy immune system becomes overwhelmed. Add to that a lack of sleep and high stress levels when dealing with an epidemic and it becomes surprising that more medical personnel do not become ill.

Strengthening the Immune System

As mentioned earlier, there are five areas of the immune system that we can improve through our actions. When these goals are met your chance of falling seriously ill can be greatly reduced.

These goals are:

  1. Enhance barrier integrity: improve the lining of our respiratory tract, gut, blood-brain barrier, and skin.

  2. Increase production of antimicrobial peptides: small amino acid linked chains that fight against infections.

  3. Promote phagocytosis: a process when white blood cells, such as macrophages, are better able to recognize and consume infected cells, microbes and/or viral capsids.

  4. Decrease inflammation and restore redox balance: lots of oxygen free radicals lead to immune imbalance and increased inflammatory products.

  5. Activate intracellular defense pathways: a process that allows cells that take on bacteria to kill them before they can replicate or cause damage (Nrf2 and SIRT1 activation.)

Before we discuss these ways to implement these goals, it helps to have a basic understanding of how the immune system works. So, here is a very simple overview of how a healthy immune system should work.

Barrier Defenses – Strengthened by Goals 1 and 2

The barrier defenses form your first level of protection and include your skin and the linings of your gut, respiratory tract, urinary tract, and reproductive tract. These are your epithelial tissues and they create a physical barrier that is difficult for pathogens to get through.

Your microbiome, antimicrobial peptides, mucous membranes, and secretions such as sweat, tears, saliva, mucus, and stomach acid are also part of the barrier defenses. They work in many ways. Some trap, sweep or wash away things that do not belong in the body. Others destroy pathogens through enzymes, acids, and other substances that are toxic to the invaders.

An internal barrier is the blood-brain barrier. Although it does not have any direct contact with the external environment, this barrier defense protects the brain from pathogens and other harmful substances in the blood.

Immune Responses - Strengthened by Goals 3, 4, and 5

Once a pathogen has passed through the barrier defenses, your body utilizes two mechanisms to destroy the pathogen, the innate immune response and the adaptive, or acquired, immune response. Both responses use different types of white blood cells to attack and destroy invaders and infected or unhealthy cells. The two responses often cooperate and influence the way each responds to pathogens.

The innate response begins immediately and can identify and destroy invaders quickly. Once an invader is identified, two innate immune responses are triggered, phagocytosis and inflammatory responses.

Phagocytosis is a process that occurs when certain types of white blood cells classified as phagocytes surround and engulf cells or particles. They do this to kill pathogens and clear an area of debris and old, infected, or damaged cells.

Acute inflammation occurs in response to infection or injury. It brings greater blood flow to the area and produces chemical factors that attract more phagocytes to destroy pathogens and clear the area. It also initiates actions that begin the adaptive immune response. The inflammatory response has specific symptoms:

  • Redness due to increased blood flow.

  • Swelling in the area of injury or infection. Swollen tonsils during tonsillitis are one example.

  • Pain in the area of injury or infection. In viral respiratory illnesses, you may notice a sore throat. It may also be felt throughout the body in the case of body aches experienced with influenza, colds, and other viral or bacterial infections.

  • Heat may be noticeable in the area of infection. Your body may respond with a fever, to raise your temperature in order to kill the virus or bacteria. Fevers also trigger other factors in the immune response.

  • Increased mucus production causing a runny nose or productive cough.

Although the symptoms of inflammation make you feel poorly, they are actually vital processes in defending the body from pathogens. Fever, a sore throat, and cough are good signs that the immune system is doing its job.

However, you do not want the responses to go unchecked, so the body has a system to mediate the inflammatory response. This is intended to keep the body from being overwhelmed by the response and prevent problems like anaphylaxis, extremely high fevers, and widespread tissue damage.

The innate immune response is vital because some pathogens can reproduce so quickly that, if your body relied solely on the adaptive response, you would have a severe infection or possibly even die before the adaptive response had time to begin working. However, because the innate response is less efficient than the adaptive response, you may experience symptoms for a longer time when the innate immune response is the primary mechanism fighting the pathogen.

The Acquired or Adaptive Immune Response

Once you have been exposed to a specific pathogen, the adaptive immune response can begin to do its work. T cells and B cells are white blood cells that learn how to attack the invader most efficiently and join the innate immune responses in fighting the pathogen. They also remember that specific pathogen so your body can fight it off more effectively and quickly in the future. This is why you may sometimes experience very mild symptoms when you encounter a cold or flu virus. Most likely, it is a strain you have already been exposed to, so your body remembers it and is able to quickly and efficiently fight it off. This system is not infallible, because some pathogens are able to disguise themselves.

Antibodies are the protein that recognizes specific antigens, which are proteins on the surface of pathogens. Once your body has encountered a pathogen, a function of the adaptive immune system is to produce antibodies that find and attach to that specific microorganism. They immobilize, kill or target the pathogen for destruction.

Antibodies are only created in response to specific pathogens. If you have antibodies for a specific strain of virus or bacteria, your body has been exposed to that strain before and should be able to recognize and quickly fight it off in the future.

Complement System

The complement system is another vital component of the immune system. It works with the innate and adaptive responses. It is a cascade of proteins that alter or fragment later proteins, in specific sequences. The cascade triggers many actions including recruiting inflammatory cells, attracting phagocytes to the area and marking pathogens for phagocytosis, damaging the plasma membrane of a pathogen leading to its death and removing neutralized antigen-antibody complexes from the body.

Cytokines are small proteins produced by cells that act as chemical messengers. They have roles in many processes, including initiating or inhibiting inflammation, regulating innate and acquired immune responses, and tissue repair.

The Pillars of Health

Now that we have explained the basics of how the immune system works, let’s go back to the 5 Pillars of Health that we previously discussed. There are specific ways that each impacts the immune system. Here are a few examples:


Adequate sleep reduces inflammation and improves the action of T cells. Conversely, not enough sleep or poor-quality sleep increases inflammation and inhibits the action of T cells.


Good nutrition is crucial for antibody production and affinity, phagocyte function, the complement system, cytokine production, and regulating inflammation and the redox balance. Adequate water intake improves blood flow and removes toxins and waste.


Moderate exercise promotes blood flow and helps white blood cells to circulate more rapidly. It also slows the release of stress hormones.

Stress Management.

Stress hormones inhibit the actions of T cells, which means they are not able to destroy pathogens as efficiently. Managing stress keeps these hormones low. Some stress management techniques also produce a direct, measurable effect on your body. For example, breathing slowly through the nose stimulates nitrous oxide production, which helps restore the redox balance.

If you need help maintaining or improving your immune system and overall health, we would be privileged to help you. We are offering Telemedicine Visits to help you stay on course with your healing journey and to address any new conditions that may come up. Additionally, our functional nutrition lifestyle educators, Cheri Hazen and Brittany Marvin, would love to assist you in staying healthy and building new habits to keep your immune system functioning well.


Jonathan Vellinga, M.D.

Jonathan Vellinga, M.D. is an Internal Medicine practitioner with a broad interest in medicine. He graduated Summa cum laude from Weber State University in Clinical Laboratory Sciences and completed his medical degree from the Medical College of Wisconsin.​

Upon graduation from medical school, he completed his Internal Medicine residency at the University of Michigan. Dr. Vellinga is board-certified with the American Board of Internal Medicine and a member of the Institute for Functional Medicine.



Brodin, P., & Davis, M. M. (2017). Human immune system variation. Nature reviews. Immunology17(1), 21–29.

Bush, L. M. (2019, February). Defenses Against Infection - Infections. Retrieved from

Delves, P. J. (2018, December). Overview of the Immune System - Immunology; Allergic Disorders. Retrieved from

Ranjit Kumar Chandra, Sobha Kumari, Nutrition and Immunity: An Overview, The Journal of Nutrition, Volume 124, Issue suppl_8, August 1994, Pages 1433S–1435S,

Rice University. (2013, March 6). 21.2 Barrier Defenses and the Innate Immune Response. Retrieved from



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