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How Does the Immune System Work?

Part-2 by: Jonathan Vellinga, M.D.

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.