How Does the Immune System Work?: A Guide

Feb 18, 2022 Immune System 4 MIN

How Does the Immune System Work?: A Guide

Quick Health Scoop

  • Your immune system defends your body
  • Comprised of the innate immune system and the adaptive immune system, this complex system of cells, tissues, and organs work together to protect you
  • The major parts of the immune system include white blood cells, lymph nodes, spleen, tonsils, adenoids, thymus, bone marrow, skin, mucous membranes, stomach, and bowel
  • The primary tasks of the immune system is to defend against harmful invaders as well as other internal changes

As someone who takes charge of your health, you know the importance of exercising regularly, getting enough sleep every night, managing stress, and eating a nutritious, balanced diet. All this helps build a healthy immune system. Staying healthy year-round depends, in large part, on the proper functioning of your immune system. When it’s working correctly, you don’t even notice. But when your immune system stops working properly, you may take notice. 

But exactly what is the immune system? And how does the immune system work?

If it’s been a few years since your high school biology class, you might want a quick refresher. 

Keep reading to learn more about how the immune system works.

What is the Immune System?

The immune system is your body’s way to defend against foreign substances called antigens that can cause infection, illness, and disease.[1] This complex and integrated system of cells, tissues, and organs work together, playing specialized roles in defending against these foreign substances or antigens.

What Are the Parts of the Immune System?

Comprised of a large network of organs, cells, and proteins, the immune system has two main parts that work together:[3] 

  • Innate immune system: This is the immune system you’re born with. 
  • Adaptive immune system: This is the immune system that develops as you age and the type of immunity that can change (or adapt) according to various factors (e.g. diet, nutritional status, etc.) your body is exposed to.

While you can see more detailed explanations of innate and adaptive immune systems below, they consist of these major parts:[1]

  • White blood cells
  • Lymph nodes
  • Spleen
  • Tonsils and adenoids
  • Thymus
  • Bone marrow
  • Skin and mucous membranes
  • Stomach and bowel

What is the Innate Immune System?

As the body's first line of defense, the innate immune system serves as a generalized rapid response system that you inherit at birth. The innate immune system contains “scavenger cells” called phagocytes, which quickly engulf and digest foreign substances as they enter the body.[3] 

Because it responds similarly to all foreign substances entering the body, the innate system is sometimes called the “nonspecific” immune system. Although general in its approach, the innate system acts quickly, such as when foreign substances enter through broken skin and are quickly detected and destroyed. The body sends these killer scavenger cells (white blood cells called leukocytes) to defend. Though limited in its ability to stop the spread of in the body, the innate immune system protects via the skin and mucous membranes as well as the defense cells and proteins.[4]

What is the Adaptive Immune System?

The body’s second line of defense is the adaptive immune system (a.k.a. the acquired immune system). It takes a more targeted approach in its fight against foreign substances, and it changes throughout your life. After being exposed to a specific foreign substance invading the body, the adaptive system produces a specific antibody (developed by cells called B lymphocytes) to protect you. While it can take several days or weeks for these antibodies to develop, once the adaptive system has been exposed to a specific foreign body, it will recognize this specific invader in the future and defend against it.[3] For instance, when you receive an immunization, they train your adaptive immune system to make a specific antibody to protect you.

The adaptive immune system protects thanks to its components, including T lymphocytes (T cells) and B lymphocytes (B cells), which are both found in the tissue between the body's cells. Some of the T cells even have special names relevant to their function, such as helper T cells and killer T cells. The adaptive system also consists of antibodies, which are compounds of protein and sugar that circulate in the bloodstream, created to fight antigens (and other foreign substances). [4] This adaptive immunity (also called acquired immunity) takes over after the innate immunity reaches its limited ability to protect against pathogens.[2]

What are the Functions of the Immune System?

Now that you understand the innate and adaptive immune system (and you know the main body parts involved), you can better understand how the immune system works. The immune system helps fight  invaders and its main tasks include:[5]

  1. Pathogens, like bacteria, viruses, parasites, or fungi, and eliminating them from the body
  2. Identifying and neutralizing harmful substances from the environment that enter the body

The body mobilizes an immune response to deal with foreign invaders. Sometimes, though, the body mounts an immune response against its own tissues instead of a foreign invader. When this occurs, it’s called an autoimmune disorder or an autoimmune disease.[2] 

The Bottom Line

How does the immune system work? Your body’s amazing immune system protects you against foreign substances. It consists of both the innate immune system and the adaptive immune system, which work together to protect you. The primary immune system cells, tissues, and organs include white blood cells, lymph nodes, spleen, tonsils, adenoids, thymus, bone marrow, skin, mucous membranes, stomach, and bowel. The primary tasks of the immune system include fighting foreign substances. 

Continue to check back on the Nature Made blog for the latest science-backed articles to help you take ownership of your health.

This information is for educational purposes only and is not intended to serve as medical advice or a recommendation for any specific product. Consult your health care provider for more information. 


  1. Cleveland Clinic. “Immune system.” February 22, 2020. Accessed on: November 29, 2021. 
  2. Oregon State University’s Linus Pauling Institute. “Immunity In Depth.” July 2016. Accessed on: November 30, 2021.  
  3. Johns Hopkins Medicine. “The Immune system.” 2021. Accessed on: November 29, 2021. 
  4. Institute for Quality and Efficiency in Health Care. “The innate and adaptive immune systems.” July  30, 2020. Accessed on: November 30, 2021.
  5. Institute for Quality and Efficiency in Health Care. “How does the immune system work?” April  23, 2020. Accessed on: November 30, 2021.


Lisa Beach

NatureMade Contributor

Lisa Beach is a seasoned journalist whose work has been published in The New York Times, Good Housekeeping, Eating Well, Parents, AARP’s Disrupt Aging, Optimum Wellness, and dozens more. She also writes for a variety of health/wellness-focused brands. Check out her writer’s website at

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Lynn M. Laboranti, RD

Science and Health Educator

Lynn is a Registered Dietitian (R.D.) and is a member of the Medical and Scientific Communications team at Pharmavite. She has over 20 years of experience in integrative and functional nutrition and has given lectures to health professionals and consumers on nutrition, dietary supplements and related health issues. Lynn frequently conducts employee trainings on various nutrition topics in addition to educating retail partners on vitamins, minerals and supplements. Lynn has previous clinical dietitian expertise in both acute and long-term care, as well as nutrition counseling for weight management, diabetes, and sports nutrition. Lynn earned a bachelor’s of science in Nutrition with a minor in Kinesiology/Exercise Science from The Pennsylvania State University. She earned a M.S. degree in Human Nutrition from Marywood University in Scranton, Pennsylvania. Lynn is an active member of the Academy of Nutrition and Dietetics, Sports Cardiovascular and Wellness Nutritionists, Dietitians in Functional Medicine, and holds a certification in Integrative and Functional Nutrition through the Academy of Nutrition and Dietetics.

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