Immune System Explained

The National Cancer Institute at the National Institutes of Health (NIH) defines the Immune System as, “A complex network of cells, tissues, organs, and the substances they make that help the body fight infections and other diseases. The immune system includes white blood cells and organs and tissues of the lymph system, such as the thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow.”

The immune system is a complicated one – it’s made of special organs, cells, and chemicals that fight infection, illnesses, or diseases. Today, we’ll go over the key players involved in this system that help to fight off infections and what happens when they are inactive or unavailable. 

Your body will help you stay healthy, as its job is to keep bad germs out of your body by either eliminating them or limiting their harm if they get in. But that’s only if your immune system is working properly.

When your immune system is doing well, it can tell which cells are yours and which are foreign to your body. Once your body is attacked by germs, it will mobilize and attack foreign invader germs that may cause you harm. If your body has done this in the past, it can recognize these germs because it has already been exposed to them, and it will help you to develop antibodies to protect you from those pesky germs. This is the purpose of a vaccine.

germs in animated body

When your immune system is NOT doing well, an infection or illness can develop. This is where it gets a little bit complicated. Do you know the feeling when you’re so tired you almost feel a little bit wired and hyper? This is your body’s way of trying to get over chronic stress or hyperstimulation. The same thing can happen with your immune system. Sometimes, it attacks when there is no invader or doesn’t stop an attack after the invader has been killed, which means it’s working overtime! This results in issues such as autoimmune diseases and allergic reactions.

Let’s learn more about the key players of our immune system and what happens to us when our immune system is not working optimally.

Key Players

White blood cells

These serve as the army against harmful bacteria and viruses; they attack and destroy germs to keep you healthy. White blood cells (WBC) either circulate in your bloodstream and throughout your body or they reside in a particular tissue waiting to be called into action. 

They’re also known as leukocytes. As these leukocytes travel through your bloodstream and tissues, they point out or notify other white blood cells of their location in order to defend your body from an attack. When the army of WBC arrives, they fight the invader by producing antibody proteins to attach to the organism and destroy it.

Fun fact: White blood cells are not white. They are actually a very light purple to pink color.


Like WBC, antibodies are fighters! They’re Y-shaped proteins that bind to your body’s foreign invaders. From viruses to parasites, they search ’em out and destroy ’em all. Antibodies are playing flag football and tackling all the bad guys. 

Antibodies are also known as immunoglobulins and are part of the “adaptive” immune system. It’s the part of your immune system that recognizes specific pathogens and eliminates them based on previous experience!

Fun fact: Antibodies come in all shapes and sizes. They’re kind of like locks because they latch onto invaders, but because they all latch onto different parts of these invaders, they all take on different shapes. They also perform different tasks once they’ve bound to a target. Some nip the infection in the bud while others simply tag them to alert killer cells to remove the infection. Some even wrap the virus or bacteria in a gooey coating!

Complement System

The complement system’s main function is to guide phagocytic cells and clear microbes and damaged cells from an organism. 

This system is also known as the complement cascade and is part of the innate immune system. This system is not adaptable and does not change throughout your lifetime. It is recruited and brought into action by antibodies generated by the adaptive immune system.

3 animated germs on light green backgroundThe complement system’s main functions are:

  1. To activate or promote inflammation (like when you get a mosquito bite)
  2. Label the pathogens and cells that need to be destroyed
  3. The direct killing of target cells/microbes by lysis (the breakdown of a cell caused by damage to its plasma (outer) membrane)

Fun fact: The complement system is like a surveillance system and plays the role of host homeostasis, trying to keep us at bay. But this system is more complicated than that, thanks to recent studies. In fact, studies over the years demonstrated that complement takes part in nearly every step of the immune reaction and that it deserves a central position in immunological research. However, that’s one of the reasons this is one of the most complicated and incomprehensible parts of immunology and why scientists choose not to study it. Ironic!

Lymphatic System

The lymphatic system is a circulatory system made of lymph vessels, similar to blood vessels. This system drains the extra fluid that has passed out of the blood and into tissues and returns it back to the blood. The lymphatic system carries big responsibilities! It is approximately twice the size of the blood circulation system, meaning it manages over half our blood volume!

Some body parts found in the lymphatic system are the tonsils, spleen, lymph nodes, lymph vessels, and even your appendix! You’ll know your body is in the throes of fighting an infection when the lymph nodes in your neck are swollen. 

Lymphatic or lymphoid tissue can be found in this lymphatic system; these tissues and organs make, store, and release lymphocytes (white blood cells, as we discussed earlier). These tissues also monitor the lymph for germs, foreign substances, and abnormal cells in order to remove waste products and bacteria from the lymph.

Lymphatic cells actually make a big difference in our gut, too. The gut is lined with millions of lymphatic vessels known as lacteals. These lacteals absorb the fats and fatty acids that you ingest and transport them to the heart where they enter the circulatory system as fuel.

Fun fact: If the lymphatic system stopped working, we would die within 24-48 hours. Yikes!


The spleen helps fight invading germs like many other key players, but specifically in the blood. It also contains infection-fighting white blood cells but also controls the number of blood cells in your body (from white, to red, to platelets), and it filters the blood and removes old or damaged red blood cells.

As you can probably guess, if your spleen isn’t working optimally, you may notice any of the following conditions:

  • blood cancers
  • blood clots
  • anemia
  • cystic fibrosis
  • infections like mononucleosis, syphilis, malaria, or endocarditic
  • liver problems (like cirrhosis)
  • Inflammatory diseases

And there’s more. We don’t talk about the spleen often but imagine your body not being able to filter out the old and damaged blood cells and having them stick around and infect your entire blood system. 

Keep your spleen happy, drink lots of water, exercise regularly, and maintain a healthy weight by eating a balanced diet. 

Fun fact: Ok, so there’s a little caveat. You can technically live without your spleen. Living without a spleen is a condition called asplenia. Sometimes, people are born without a spleen. Other times, the spleen will be removed surgically (through splenectomy) due to damage or disease. In this case, the liver will take over the spleen’s duties. If you’ve gone through a splenectomy, you may have a higher risk of infection because your body will have a harder time protecting itself from infection. 

Bone Marrow

This sponge tissue is found inside your bones. It produces red blood cells that our bodies need to carry oxygen, the white blood cells used to fight infection, and the platelets we need to help reduce blood clots.

It also contains stem cells that circulate in your veins and arteries. They’re also known as peripheralanimated sanitizer on germs blood stem cells (PBSC), which are found in relatively large numbers in those recovering from chemotherapy or other healthy people who are treated with drugs to stimulate bone marrow growth. The PBSC can be collected and used as a source of stem cells for transplantation. 

If you are suffering from fever, fatigue/weakness, increased infections, shortness of breath, or are easily bruised or bleeding, your bone marrow could be affected and, in turn, affect your healthy blood cell count.

As you age, your bone marrow (red) is gradually replaced with yellow bone marrow. Yellow bone marrow is involved in the storage of fats which can be used as an energy source when needed.

Fun fact: A bone marrow transplant can save the life of someone battling leukemia, lymphoma, or another blood cancer. You can fight cancer just by swabbing your cheek. Sign up for Give a Spit About Cancer. The likelihood of finding a donor is estimated at 66% for African-American patients, 72% for Hispanics or Latinos, 73% for Asian and Pacific Islanders, 82% for American Indian and Alaska Natives, and 93% for white patients. To be a bone marrow donor in America, a person should be between 18 and 60 years old and in good health – young people under 25 years old are the bone marrow donors needed most!).


This is one of those special organs that actually shrinks as you age rather than grow. This little guy is part of the lymphatic system so I won’t go too into detail, but this one is important because it trains special white blood cells known as T-cells. These white blood cells actually start as lymphocytes traveling from your bone marrow to your thymus, and it’s there that they turn into T-cells. 

These T-cells travel to your lymph nodes and other parts of the lymphatic system where they help your immune system fight disease. Not only is it part of the lymphatic system, but also the endocrine system, which makes and releases hormones that control your bodily functions. 

The thymus and thyroid are not interchangeable. These are two different organs. The thymus helps protect the immune system, while the thyroid produces hormones that control your growth and metabolism.

Fun fact: As an adult, you don’t need a thymus since most of your T-cells were produced before you were even born and the rest were made throughout puberty. Removing your thymus as a child can cause potential health issues like infection, autoimmune conditions, allergies, and an increased risk of cancer.

Common Disorders

There are 2 common disorders of the immune system. They are allergic diseases and autoimmune diseases, many of which we have encountered either personally or through friends or family. They are not uncommon!

Allergies: You know the feeling; coughing, runny nose, or sometimes a life-threatening reaction such as anaphylaxis. This happens when your body develops antigens against a substance, such as dust, pollen, or bee stings. Your immune system may overreact by producing antibodies that “attack” the allergen. Hormones, stress, smoke, perfume, and environmental irritants can play a role in the development or severity of allergies.

Autoimmune disease: This happens when your body’s natural defense system can’t tell the difference between your own cells and foreign cells. Your body ends up attacking normal cells by accident. There are over 80 different types of AI diseases. Autoantibodies are released which end up attacking healthy cells.


person applying hand sanitizer

This was a pretty long one, and we went through the basic functions of some of the key players in the immune system. I didn’t want to get too in-depth but wanted to what could happen when the immune system is struggling to work optimally and why that might be. 

Some simple ways to keep the immune system healthy are as follows:

  • Quit smoking
  • Maintain a healthy body mass (or just eat healthily and get blood tests done frequently – honestly, I don’t think that thin equates to health)
  • Drink alcohol in moderation or avoid it entirely
  • Get enough sleep
  • Exercise regularly
  • Wash your hands often
  • De-stress by focusing on mindfulness
  • Get vaccinated (I know people are on different pages on this and some may have reasons they would prefer not to)

If you have any questions about Immune System optimization or think that I could have explained something better in this article, leave me some feedback in the comments! I’m still trying to learn a bit more about my own body, so I felt compelled to write a little about what I was reading and watching. Check out the resources below if you want more learning materials.



Alexia Palmeri

Alexia Palmeri is a 28-year-old personal development enthusiast! She looks at life experiences as an opportunity to always learn and grow. Alexia is also a broadcast journalism graduate with a passion and knack for communications and media. She is always on the lookout for new trends on social media and keeps up to date with what's happening in the world. In her free time, Alexia enjoys socializing with family and loved ones, being in nature, cooking nourishing meals, and discovering new places to dine and adventure!

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