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We Asked an M.D.: How Does The Immune System Work?

By Stephanie Eng-Aponte

Reviewed by Dr. Pamela Peeke, MD, MPH, FACP, FACSM


Lately, there’s been a lot of talk about ways to boost your immune system. But how does your immune system work and what exactly does it do? The immune system’s main goal is to protect your body from infection and disease. It’s not just limited to one part of the body: It’s actually a network of cells, tissues and organs that work together to fight off substances, germs and other cell changes that could make you sick.1


We sat down with Dr. Pamela Peeke, MD, MPH, FACP, FACSM and chair of Jenny Craig’s Science Advisory Board to learn how the immune system works, what could weaken it, and how to give it a boost.

How does the immune system work?

Many parts of the body, including organs, tissues and cells, are essential for a strong and healthy immune system. The immune system helps to protect against threats both inside and outside of the body and has three main jobs:1


  1. To fight disease-causing germs, including bacteria and viruses;
  2. To recognize and neutralize harmful environmental substances;
  3. And to fight disease-causing changes within the body.



“Your immune system is your body’s natural defense system,” states Peeke.


Any substances that your body doesn’t recognize, such as bacteria, are called antigens. Antigens trigger an immune response, which helps to defend your body against illness. When your body encounters a harmful antigen for the first time, it typically stores information about the threat and how to fight it. If you come into contact with the same germ again, your body is able to recognize and attack it faster.1


ImmuneSystem_Main_Photo by Sarah Gualtieri on Unsplash_resized.jpg

Photo by Sarah Gualtieri on Unsplash

Key parts of the immune system

Your immune system has two parts, the innate immune system and the adaptive immune system. Each part uses specific tools to help keep you healthy.


The innate immune system:1

  • Is your body’s first line of defense against pathogens (bacterium or viruses that can cause disease);
  • Uses physical barriers (like skin), chemical barriers (like mucus and stomach acid) and bacterial “partnerships” to keep germs out or destroy them; and
  • Utilizes a variety of immune system cells to find, trap and destroy pathogens (antigens that cause disease and illness).


The adaptive immune system:2

  • Is your body’s second line of defense when pathogens aren’t destroyed by the innate immune system;
  • Helps to stop the current infection by creating and employing “memory cells,” or antibodies, to help the body to stop or lessen the pathogen’s effect in the future; and
  • Uses powerful cells to combat the threat.

What can weaken your immune system?

If an immune response doesn’t activate when it’s needed, you could be at risk for an infection.3 It’s not always clear why your immune system doesn’t work as it should,4 but many factors could play a part. Your immune system can also weaken with age,5 so it’s important to practice healthy habits to support it.


Changes to your diet and lifestyle, like increased stress and unhealthy sleep habits, may also affect your immune system and your health.


Did you know there are actually different kinds of stress? Managing daily life is associated with many short-term stresses that can be handled by adapting and adjusting to challenges as they arise. However, whenever a stress is perceived as associated with feelings of helplessness, hopelessness or defeat, then it becomes toxic stress. This kind of stress, which is often chronic long-term stress,  can increase your body’s levels of pro-inflammatory cytokines,6 proteins released by cells that can affect the way your cells communicate and interact.7 Normally, inflammation is a necessary process that helps to destroy disease-causing bacteria, viruses and microorganisms, but chronic inflammation associated with toxic stress may negatively affect your body’s immune response.6



“Prolonged, toxic stress will increase stress hormone (cortisol) levels, and the result is impaired immunity,” Peeke explains.



Photo by mapodile on iStock



Try this: These helpful tips to de-stress can be done right at home.


Lack of sleep and poor sleep quality

If you’re not getting enough shut-eye, your immune system could become compromised. One study exposed participants to the common cold and found that people who slept less than seven hours per night were almost 3 times more likely to develop a cold than those who slept for eight hours or more.8 The researchers concluded that poor sleep efficiency (“the percentage of time a person actually sleeps between lying down to sleep and waking up the next morning”), and a shorter sleep duration may be linked to a lowered resistance to illness.



“Studies show that people who are sleep deprived pick up infections more easily and can have an extended recovery from illness. On average, seven hours seems to be the ideal amount of high-quality restful sleep you need,” Peeke says.


Experts at the National Sleep Foundation agree, recommending that adults get 7-9 hours of sleep each night.9



Try this: These sleep hygiene tips could help you build better sleep habits for a good night’s rest.

How can you strengthen your immune system?

If you’re making time to de-stress and are getting plenty of restful sleep, you’re already on the right track. Here are more tips to help your immune system function at its best.

Enjoy a balanced diet

Eating a balanced diet is another way to support your immune system, all while building healthier habits — and even supporting weight loss efforts — along the way.



Photo by Rebecca Hansen on Unsplash



“Whole foods filled with high-quality carb, fat and protein are key. Add lots of leafy greens and vegetables in general. Keep in mind that it’s perfectly fine to buy frozen vegetables and fruits as they maintain an optimal amount of their valuable vitamins and nutrients,” Peeke says.


And if it’s tough to find fresh or frozen produce that you like, you can reach for healthy non-perishable foods instead.



“Don’t forget canned foods such as salmon, mackerel, sardines, lentils, pumpkin, artichokes, black or kidney beans, tomatoes and spinach. Canned fruit is another excellent option. Just make sure it’s not packed in sugary syrup. Water packed is the best,” she says. “Read the nutrition labels carefully to spot added sugar.”

Stick to your weight loss goals

If weight loss is on your mind, research suggests that it may be another way to help bolster the immune system.10,11


“Science has also shown that excess body fat, particularly abdominal fat, triggers the production of 'pro-inflammatory' immune cells, which circulate in the blood and can impair immunity and damage our bodies,” Peeke explains.



“Researchers have found that if you’re overweight or obese, a reduction of 15 pounds can begin to normalize inflammatory promoting factors, the same factors implicated in the development of heart disease. Fat tissue is also implicated in the development of chronic metabolic diseases such as Type 2 diabetes as well as heart disease. Obesity is therefore an underlying condition associated with inflammatory and metabolic diseases. Consuming a healthy diet along with increasing routine physical activity will help reduce excess body fat and optimize immune function.”


Check out these extra tips to help boost your immune system.


Try practicing a variety of healthy habits to feel your best and keep your immune system strong. If navigating a balanced diet seems challenging, Jenny Craig can help. Enjoy delicious, chef-crafted meals, easy-to-follow menus designed by nutritionists and dedicated support from a personal weight loss coach. Get meals delivered right to your door starting at just $12.99 a day!





[1] https://www.ncbi.nlm.nih.gov/books/NBK279364/

[2] https://www.chop.edu/centers-programs/vaccine-education-center/human-immune-system/parts-immune-system

[3] https://www.niaid.nih.gov/research/immune-system-overview

[4] https://health.clevelandclinic.org/can-immune-system-go-haywire-falter/

[5] https://medlineplus.gov/ency/article/004008.htm

[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465119/

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785020/

[8] https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/414701

[9] https://www.sleepfoundation.org/articles/how-much-sleep-do-we-really-need

[10] https://www.livescience.com/9877-losing-weight-helps-immune-system.html

[11] https://www.nbcnews.com/better/health/health-benefits-losing-just-5-percent-your-body-weight-ncna836056


Stephanie Eng-Aponte

bio-photo-stephanie.jpgStephanie Eng-Aponte is a copywriter for Jenny Craig and has written for the health and wellness, tech, and environmental industries. Stephanie graduated from Rutgers University with a Bachelor of Arts degree in Journalism and Media Studies. They employ an “eat first, write later” approach to food blogging and enjoy the occasional Oxford comma. Outside of writing, you can find them photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.

Favorite healthy snack: green apple slices with sunflower butter


Dr. Pamela M. Peeke, MD, MPH, FACP



Dr. Peeke is chairman of the Jenny Craig Science Advisory Board, Pew Foundation Scholar in Nutrition and Metabolism, Assistant Clinical Professor at the University of Maryland, School of Medicine, and a Fellow of the American College of Physicians. She is an internationally recognized expert, physician, scientist and New York Times best-selling author in the fields of public health, nutrition, fitness and weight management.




This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and reviewed by certified professionals.


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on the topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source.


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