April 23, 2020

How Your Amazing Immune System Protects You From Infection

Understanding how it works can help you stay healthy

A man shielded from disease by his immune system

You may not think about it very often, but your body is surrounded by danger.


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Danger can be external, in the form of infections from bacteria, viruses and other organisms. Danger also can be found internally. Our systems are designed to neatly remove our waste — but if they can’t, we suffer from inflammation, a physiologic effect that feeds numerous chronic diseases.

Today, more than ever, in the face of the COVID-19 pandemic, you might be wondering what you can do to strengthen your defenses. Your first and best line of defense against all of these dangers is a healthy immune system.

Learning how to keep your immune system strong is the best strategy for optimal self-defense and good health as you age, according to rheumatologist Leonard Calabrese, DO, who heads Cleveland Clinic’s Section of Clinical Immunology.

Here’s what he had to say.

Q: What is your immune system?

A: Your immune system is a highly integrated physiologic system that protects you from internal threats as well as external threats such as infections, toxins and malignancies. It plays a key role in helping you grow, develop and live longer, and it stays on alert for anything that threatens your health.

Think about it: We are literally teeming inside and out with trillions of microorganisms, and it’s our immune system that has to figure out which are harmful, which are neutral and which are helpful to our bodies. When working properly, your immune system ignores the helpful bacteria in your body and targets the bad.

Infections like COVID-19 are new in our society, so our immune systems have no previous experience or “memory” for them, meaning we are all vulnerable to acquiring this serious infection.


Q: How does the immune system work?

A: Your immune system is highly complex and is integrated into virtually every other organ system. It has multiple components, including the coverings of our body internally and externally, which are alive with intricate defenses. It also has a rapid response team known as the innate immune system. Finally, when these defenses are not enough, it has a highly refined and specific set of defenses known as the adaptive immune system, which can target danger signals with great precision and accuracy. Vaccinations activate the adaptive immune system and protect us from future invaders.

Q: What happens during an immunological response?

A: Your immune system can react in a variety of ways. First and foremost, it does everything it can to repel dangerous threats and get rid of them promptly on its own.

Consider two radically different scenarios:

  • A localized infection with a bacterium such as staph or strep may induce an inflammatory response, such as a boil.
  • A generalized infection such as the flu may stimulate a generalized attack and result in an inflammatory response, such as a fever.

Inflammation can help your body fight an acute and specific threat, but long-term inflammation is not good for you. Factors such as poor diet, obesity and a sedentary lifestyle make inflammation worse. As a result, chronic inflammation can hasten cardiovascular disease, cognitive decline and premature aging.

Sometimes your immune response isn’t strong enough to fully fight off an infection, which makes it harder for your body to recover. This can be referred to as an immunodeficiency when it’s severe.

At other times, immune responses go overboard. When this happens, the immune system can’t distinguish between your body and its invaders, and autoimmune disease develops.

Examples of autoimmune disease include:


Q: Why do older people do worse than younger people when infected with COVID-19?

A: The immune system works at its peak during our reproductive years, and it declines as we age. This means that older people have compromised immune systems, in general, which makes them more susceptible to getting infections and also more prone to complications when they do.

The interesting and important aspect of this is that, across the population, people differ in their “immunologic ages.” Just like some people have bodies that look much younger than their age, some people also have immune systems similar to those in younger age groups that are better defenders against danger, including COVID-19.

Why some immune system age faster than other is still not completely understood, but lifestyle and behaviors like diet, exercise, sleep and psychosocial stressors have a lot to do with it. Also important is avoiding clear negative factors to immune health, including excesses of drugs, alcohol, tobacco and other toxins.

Q: What threatens your immune system?

A: Although no drug or supplement can maximize your immune system and make it run perfectly, you can take steps to optimize how well yours works.

  • If you smoke, quit. It’s the single, biggest, most avoidable threat to your immunological health.
  • Limit excess alcohol, as well as any drugs that might compromise your immune system.
  • Avoid carcinogens as much as you can, including too much sun exposure.
  • If you’re overweight, drop those pounds because they are known to boost inflammation.

Q: What are the best ways to boost your immune system?

A: Unfortunately — and despite what you might hear or read on the internet — there are no quick fixes to boost our immune health. The good news, however, is that we can gain immune strength by focusing on exercise, diet and nutrition, and managing our mental health and stress levels. An exciting amount of work is going on in each of these areas proving that, like other physiologic systems, you can train and maintain your immune system for optimal health.

It’s essential that each of these critical areas be optimized to achieve improved health.

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