What is the Immune System?

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- Updated by Sarah Qaiser
Medically reviewed by Dr Sidra Samad

The immune system is a complex network of cells, organs, and internal systems. The immune system protects the body from foreign substances, such as antigens, viruses, and infectious diseases. There are three main types of immune systems, which are the Innate Immune System, such as the cough reflex, the Adaptive Immune System, which is how your immune cells create antibodies to neutralize every new antigen that enters the body, and the Passive Immune System, which is antibodies you have but don’t create, such as from vaccines.

Parts of the Acquired Immune System are the adenoids, bone marrow, lymphatic system, spleen, appendix, tonsils, and white blood cells that all work together to protect the body from pathogens. Antibodies are an important part of the immune system as they are produced by white blood cells, latch onto antigens, and stop them from infecting the body. Foods such as probiotics (kefir and yogurt) and prebiotics (bananas, onions) help strengthen your immune system by increasing your helpful bacteria colonies. Supplements such as Vitamin D and NAD also help strengthen your immune system as Vitamin D strengthens monocytes and macrophages, while NAD helps decrease inflammation.

How Does the Immune System Work?

The immune system works by getting rid of foreign substances, also known as antigens, when they are detected in the body. The immune system can get rid of antigens, such as chicken pox, by creating antibodies. Antibodies are a type of protein that is created by B lymphocytes to target specific antigens. B lymphocytes are a type of white blood cell, that is a part of the immune system, and are in charge of making antibodies. Once an antibody has been made for an antigen, your body won’t become sick from the same antigen again, as the antibody stays in your system just in case the same antigen comes again.

What are the Types of Immune Systems?

There are three different types of immune systems, which are listed below.

  • Innate Immune System - The Innate Immune System is what your body’s natural defenses are in regard to protection from viruses and disease.
  • Adaptive Immune System - The Adaptive Immune System is in charge of creating specific antibodies to target specific antigens, and to stop infectious diseases.
  • Passive Immune System - The Passive Immune System results from having antibodies that are not created by you, yet still offer the same level of protection.

1. Innate Immune System

The innate immune system is the first step in understanding what is the immune system made up of, as it is the immune system everyone has from birth. The innate immune system is made up of barriers and is considered to be your body’s first line of defense against diseases, according to the NIH National Library of Medicine on their paper regarding the innate and adaptive immune system in 2020. The barriers that protect you from disease include your cough reflex, the enzymes in your tears and skin, your mucus, which traps germs, and your stomach acid. There is an additional part of the innate immune system that causes fevers for protection against sickness, which is a protein called interleukin-1. If an antigen gets past these defenses, the adaptive immune system takes over.

2. Adaptive Immune System

According to Jean S. Marshall from Dalhousie University regarding their research on immunology in 2018, the adaptive immune system can better help us understand what is the purpose of the immune system in how it protects the body by creating antibodies. The adaptive immune system is made up of T cells, APCs, and B cells, all of which work together to identify antigens, and create specific antibodies to neutralize antigens.

3. Passive Immune System

The passive immune system is a result of antibodies that your body has but were created in another body. An example of the passive immune system is in a small child, which receives the antibodies of their mother through the placenta, according to CDC Centers for Disease Control and Prevention in their paper regarding immunity types in 2021. Antibodies received in this way are not permanent, and typically disappear in the following weeks or months.

What are the Parts of the Acquired Immune System?

The parts of the acquired immune system are not present at birth and are what the body learns from defending from foreign antigens over time. A list of components for the acquired immune system is below.

  • Adenoids - Located in the back of the throat, adenoids help children fight against infection.
  • Bone marrow - Bone marrow is where white blood cells and immune cells are produced.
  • Lymph nodes - Located all through the body, lymph nodes filter through fluid and remove foreign substances.
  • Lymphatic vessels - Located all through the body, lymphatic vessels transport fluids back to the lymph nodes to be filtered.
  • Peyer patches - Found in the small intestines, Peyer patches check the immune health of the intestines based on the food that is eaten.
  • Spleen - The spleen filters the blood, removing damaged red blood cells, pathogens, and other foreign substances.
  • Thymus - Located in the lymphatic system, the thymus helps create and train the body’s T cells, which go on to protect the body from pathogens.
  • Tonsils - Located at the back of the throat, the tonsils help catch and neutralize pathogens that are inhaled.
  • Leukocytes - Leukocytes are white blood cells that are divided into many groups that each help the immune system find and destroy pathogens.
  • Appendix - Located in the intestinal area, the appendix stores symbiotic bacteria that can be used in the case of an outbreak to boost the immune system.
  • Phagocytes - Phagocytes help in the early and late stages of an immune response by ingesting and destroying pathogens and debris.
  • Lymphocytes - Lymphocytes are in charge of destroying infected cells, and neutralizing antigens by creating specific antibodies.

1. Adenoids.

Adenoids are a part of the immune response in children and are located behind the nasal passage, close to the tonsils. Adenoids are useful for stopping germs and antigens as they travel through the nose and mouth. Adenoids are lymphatic tissue that helps children between the ages of 3 and 8 fight off infections before the body develops another way to fight antigens. By the time a child develops into an adult, the adenoids disappear.

2. Bone marrow.

Bone marrow is important for the acquired immune system as it is in charge of producing white blood cells, red blood cells, and platelets, according to Ende Zhao from the University of Michigan School of Medicine in 2011. A lymphocyte, which is a type of white blood cell, is continuously produced in the bone marrow and is in charge of targeting antigens by creating immune system antibodies. Antibodies are able to latch on to antigens and neutralize them. These cells produced in the bone marrow have to be produced continuously as they do not survive long in the body.

3. Lymph nodes.

Lymph nodes are located all throughout the body, such as the neck, chest, and abdomen, and are in charge of filtering and removing foreign substances. Lymph nodes carry immune cells that are able to neutralize germs, cancer cells, and other foreign substances.

4. Lymphatic vessels.

Lymphatic vessels are found throughout the body and are in charge of circulating fluids, or lymph.  Lymph vessels that are larger in size have muscles to help control the direction of flow, allowing the vessels to take the lymph back to the lymph nodes, where the lymph is then filtered.

5. Peyer patches.

Peyer patches are found in the small intestine and are in charge of sampling the food that passes through the small intestine to determine if there are infections, germs, or pathogens that need to be neutralized. Peyer patches are filled with macrophages, T cells, B cells, M cells, and dendritic cells, which all help in a healthy immune system. M cells are specialized to feed potential pathogens to the dendritic cells and macrophages, which then show the pathogen to the T cells and B cells. After checking the pathogen, the T cells and B cells determine if the pathogen requires the immune system to be signaled to attack it.

6. Spleen.

The spleen is found in the top left area of the abdomen and is in charge of filtering the blood for faulty red blood cells, bacteria, viruses, or other pathogens. The spleen is an important part of your immune system as, when pathogens are detected, the spleen works with the lymph nodes to create antibodies that neutralize the pathogen.

7. Thymus.

The thymus helps us understand what is the immune system by how it creates T cells, according to Puspa Thapa, Ph.D. from the Columbia University Medical Center. The thymus is located in the lymphatic system that specializes in creating and training all the T cells necessary for an average lifespan. Most T cells are created by the thymus before a person is born. The thymus trains white blood cells that arrive from the bone marrow until they mature into specialized T cells (T lymphocytes) that are capable of neutralizing pathogens.

8. Tonsils.

The tonsils' purpose of the immune system is to stop germs from entering the body through the nose or mouth, according to the NIH National Library of Medicine in 2011. The tonsils are located at the back of the throat and are filled with white blood cells, which are able to neutralize pathogens.

9. Leukocytes

Leukocytes (white blood cells) help us understand what is the job of the immune system by how they specialize in responding to and neutralizing pathogens, viruses, and other foreign substances. Leukocytes are found in the blood and lymphatic system and are divided into sub-groups, such as the T cells, B cells, and natural killer cells, all of which contribute to a functional immune system.

10. Appendix

The appendix offers a key indicator of how does the immune system protect the body from disease in how it interacts with the intestinal immune system, according to I. A. Kooij from the Academic Medical Center in 2016. The appendix is a safe house for symbiotic commensal bacteria, which allows these bacteria to be reintroduced into the intestines if there is a pathogen or disease. Commensal bacteria that are protected in the appendix are able to supply the intestines with nutrients and help fight against pathogens.

11. Phagocytes

Phagocytes play a vital role in the body's immune system during both the early and late stages of the immune system’s response to targeting and attacking a pathogen. Phagocytes are divided into neutrophils and monocytes, both of which are a type of immune cell, along with a few other groups. Phagocytes travel through tissues to eat and destroy microbes and debris. Phagocytes destroy this eaten material with the use of reactive oxygen species inside the phagocytes.

What are the Types of Phagocytes?

There are many types of phagocytes, according to LibreText Medicine in 2020, that help with immune system functions, all of which are listed below.

  • Monocytes - Monocytes are in charge of eating foreign substances and showing potentially dangerous antigens to other immune system cells.
  • Neutrophils - Neutrophils, once activated, travel to the sight of infection and ingest pathogens and antigens. Neutrophils are also able to cause cytotoxic damage that affects pathogens but results in the death of the neutrophil afterward.
  • Macrophages - Macrophages are found in almost all the tissues and organs of the body, and act as a delayed response from an inflammatory response, cleaning up debris and neutralized neutrophils.
  • Dendritic cells - Dendritic cells are mainly found in areas close to the external environment, such as the skin, which when activated, move to the lymphoid tissues to show antigens to T cells and B cells.
  • Mast cells - Along with being able to ingest and neutralize their antigens, mast cells are also able to create an inflammatory response when it detects an antigen, such as an allergic reaction.
12. Lymphocytes

Lymphocytes are an important part of the immune functions as they are a type of white blood cell that attacks pathogens and neutralizes cells that have been taken over by pathogens.

What are the Types of Lymphocytes?

There are two main types of lymphocytes, according to the NIH National Cancer Insitute NCI Dictionaries, that help us understand what’s the immune system and the role they play in it.

  • B Cells - B cells are in charge of producing antibodies that destroy pathogens, viruses, and other foreign substances.
  • T Cells - T cells are in charge of neutralizing the body’s cells, specifically those that are controlled by pathogens or have become cancerous.
What are B Lymphocytes?

The immune system is made up of B lymphocytes, or B cells, that create antibodies, which are a type of protein that binds to antigens to destroy them. Antibodies do this by attaching to a virus, preventing that virus from entering a cell and causing damage.

What are T Lymphocytes?

T cells are in charge of neutralizing infected body cells, or cancerous body cells, and assist B cells in destroying pathogens. T cells also have a sub-group called Memory T cells, which help your body rapidly recover if the same antigen tries to infect the cells again/ Memory T cells will remember the antigen and know how to neutralize it.

There is a weakening effect linked with T cells, antibiotics and immune system, as antibiotics are known to weaken the immune system’s defenses by reducing the memory of T cells.

What Does the Immune System Fight Against?

The immune system fights against a myriad of pathogens and diseases, and helps us understand are antibodies part of the innate immune system or not. Antibodies, which help fight against pathogens, are created by both the acquired immune system and the innate immune system. A list of pathogens and other substances the immune system fights against are below.

  • Infections - Bacterial and virus infections invade the body and have to be countered by the immune system.
  • Toxins - Byproducts from certain bacteria are toxins, causing damage and requiring removal by the immune system.
  • Genetic Problems - Genetic problems like an autoimmune disease can inhibit the immune system and how it functions.
  • Physical Damage - Physical damage can cause inflammation and tissue damage, requiring the immune system to step in and help repair the damage.

1. Infections

Infections are when invading bacteria or viruses attack the immune system body, multiplying rapidly, according to Johns Hopkins Medicine. A few examples of bacterial infections are strep throat, tuberculosis, and urinary tract infections. A few examples of virus infections are the common cold, chicken pox, and AIDs. Infections range from mild to dangerous, like AIDs, which has the potential to be life-threatening. For the most part, however, the immune system is well-equipped to neutralize infections.

2. Toxins

Toxins are made from single-cell organisms like bacteria that are toxic to humans. Antibody-producing cells show us how the immune system works by targeting and removing toxins, according to the Better Health Channel, in association with the Victora State Goverment’s Department of Health in 2022. An example of a toxin is cholera, produced by cholera bacteria. If left untreated, cholera could be quite dangerous as it causes the body to become severely dehydrated. 

3. Genetic Problems

Genetic problems are often inherited and are present at birth. According to the University of Rochester Medical Center’s Health Encyclopedia, genetic problems affect how the immune system functions, such as having an autoimmune disease that attacks the body’s healthy cells instead of pathogens. Specific genetic problems, such as the autoimmune system disorder Multiple Sclerosis, can be potentially life-threatening. To learn who has the strongest immune system in the world, it’s important to look at how the immune system functions. A lack of genetic problems and the ability to bounce back quickly from sickness and wounds is an indicator that the immune system is functioning at its best.

4. Physical Damage

Physical damage, such as a bee sting, shows how does the immune system work in the body by first detecting the physical damage at the sting site. According to Dr. Akinori Osuka from the Harvard Medical School and Osaka University, physical damage is addressed by immune cells like T cells and B cells, which produce antibodies to remove bacteria and toxins. These immune cells also repair physical damage by producing cytokines which repair tissue and fight off pathogens.

What are the Functions of the Immune System?

The functions of the human immune system are below.

  1. The immune system can tell which cells are yours, and which are foreign.
  2. The immune system is able to take action against foreign substances by mobilizing and attacking foreign substances.
  3. After fighting an antigen or foreign substance once, the immune system remembers how to fight that antigen next time. An example of immune system memory is with vaccines, where the body builds up antibodies against a vaccine’s dead cells, and will remember how to fight that infection if the same cells invade the body again.
How Does the Immune System Change According to Age?

The immune system changes according to age in its decrease in activity as the body gets older, according to  Peter J. Delves, PhD, from the University College London. He states that age causes the white blood cell count in the body to decrease, and T cells to react slower to antigens. The immune system helps us understand what does the immune system do in how it heals, repairs, and neutralizes threats. An increase in age results in the body healing slower, slower ability to bounce back from sickness, and fewer cell defects being found and corrected.

What are Immune System Antibodies?

Antibodies are an important immune system function as they are in charge of protecting the body from foreign pathogens, according to MedlinePlus, a division of the National Library of Medicine. Antibodies are produced by the immune system and attach to antigens and foreign substances, removing them from the body.

What are Immune System Responses?

Immune system responses are how the body responds to pathogens in the body. Immune system responses are varied, but the most common is the creation of antibodies to neutralize pathogens. To learn how long do antibodies stay in your system, Natalia Herrero, Ph.D., from the University of Bern in 2021, states in their research that antibodies like Covid can last in the body for around seven months.

Why is Immunization related to Immune System?

Immunization plays a powerful role in the immune system by causing the immune system to react to a pathogen without the body becoming sick. Immunization comes in the form of a vaccine which gives the body a dead antigen to create antibodies against, which in turn teaches the immune system how to rapidly respond to the antigen if it is seen in the body again. The role of antibodies in the human body is to latch on to antigens and prevent them from multiplying or causing harm, eventually flushing them from the body.

What are Some Immunization Examples?

Some examples of immunization that help create specific antibodies immune system are listed below.

  • Chickenpox vaccine - Mostly seen in children under the age of 12 that are unvaccinated, chickenpox causes fever and blisters. The chickenpox vaccine immunizes the body so it's not possible to become sick from chickenpox.
  • Hepatitis B vaccine - An infection in the liver, hepatitis B causes fever, tiredness, and loss of appetite. A hepatitis B vaccine immunizes the body so it’s not possible to become sick from hepatitis B.
What is the Immune System made up of?

The immune system is made up of organs, white blood cells, and proteins. To learn what is the function of the immune system, one has to look at how parts of the immune system protect the body from becoming sick. The immune system, with a combined effort from the spleen, bone marrow, appendix, lymphatic system, and other parts of the immune system, protects the body from foreign substances.

What affects the Strength of the Immune System?

There are a few factors that affect the immune system, which are listed below.

  • Vaccines - Vaccines are able to boost the immune system by making it easier to fight infections and diseases. An example of a vaccine can be found in the Covid virus. To learn how long do covid antibodies stay in your system, a vaccine that creates antibodies for covid typically lasts several months or longer.
  • Smoking - Smoking is known to damage the equilibrium of the immune system, weakening the body’s ability to respond to sickness.
  • Alcohol - Alcohol weakens the immune system by damaging specific types of white blood cells. 
  • Poor nutrition - Poor nutrition affects the immune system by mitigating the amount of nutrition the system needs to function properly, leading to a weakened immune system and increased susceptibility to disease.
  • Viral infections - Viral infections such as AIDS can drastically affect the health of the immune system, destroying the white blood cell’s ability to defend the body.
What are Immune System Disorders?

Immune system disorders are factors that inhibit the immunology system’s ability to perform and protect the body from infection. A list of known immune system disorders is below.

  • Immunodeficiencies
  • Autoimmunity
  • Hypersensitivity

1. Immunodeficiencies

Immunodeficiencies are when the immune system isn’t able to protect the body against diseases. In an immune system diagram, Immunodeficiencies can be seen as a lack of immune system components, such as white blood cells, present to function and protect from pathogens. Types of immunodeficiencies are classified by the part of the immune system that is lacking, like Humoral immunity, which means a lack of B cells, or Cellular immunity, which means a lack of T cells.

2. Autoimmunity

Autoimmunity means the immune system confuses parts of your body for pathogens or a foreign substance and attacks healthy cells. Antibodies are produced but are used against healthy cells. To understand how do you get antibodies you have to look at white blood cells, which are in charge of attacking viruses and pathogens, and in turn, produce antibodies. There are a few types of autoimmune diseases, such as Type 1 diabetes, which means the immune system attacks and destroys insulin-producing cells. Another type of autoimmune disease is rheumatoid arthritis, which is where the immune system attacks the body’s joints.

3. Hypersensitivity

Hypersensitivity is regarded as an over-active or over-sensitive immune system and causes uncomfortable or damaging reactions in the body. Hypersensitivity overrun the basics of the immune system by making the immune system fail to function correctly, and sometimes even harmfully against the body. There are four main types of hypersensitivity, such as Type I, which is a IgE reaction (a type of antibody), Type II, which is an antibody-mediated reaction, Type III, which is an immune complex reaction, and Type IV, which is a delayed reaction that is cytotoxic.

What are the Best Foods for Immune System Strength?

According to a paper written by Harvard on what a healthy diet looks like, the following foods below are the best for immune system strength.

  • Probiotic foods - Probiotic foods are useful for immune system strength as they contain helpful live bacteria that aid and strengthen the microbiome and immune system. Some examples of probiotic foods are kefir, fermented vegetables, and kombucha.
  • Probiotic foods - Prebiotic foods provide the fiber that feeds and supports helpful bacteria. Some examples of prebiotic foods are garlic, onions, and bananas.

This can describe another function of the immune system as the immune system is dependent on outside sources such as the diet to supplement it with the right nutrients to function properly.

What are Good Supplements for the Immune System?

Good immune system supplements are listed below.

  • Vitamin D - Vitamin D is a good immune system supplement as it empowers the monocytes and macrophages in your system, and decreases inflammation.
  • Zinc - Zinc is a good immune system supplement as it is a necessary ingredient for the body’s inflammatory response, and helps prevent pathogens from entering the body by protecting the tissue barrier.
  • Vitamin C - Vitamin C is a good immune system supplement as it empowers immune cells to better fight pathogens and aids in clearing out deceased cells and producing new cells.

How does Nicotinamide Adenine Dinucleotide (NAD) Help Make a Stronger Immune System?

NAD can be used as immune system medicine to help make a stronger immune system as it has a direct impact on the inflammatory response. Nicotinamide Adenine Dinucleotide (NAD) affects the inflammatory response of the immune system by controlling sirtuins. 

How Do Antibiotics Help in Fighting Against Infections?

Antibiotics help in fighting against infections by taking down live hostile bacteria and aiding the types of immune system. Antibiotics aren’t able to kill a virus as a virus is considered to be non-living, but antibiotics can fight and neutralize bacterial infections. Antibiotics are only able to destroy the specific bacteria they’re designed for, which is why specific prescriptions are required depending on what type of bacterial infection the body has.

How Does the Immune System Use ATP?

The immune system uses ATP within its cells to power immune system responses. ATP powers responses such as phagocytosis, processing antigens, and phosphorylation.

What Should You Know About the Immune Systems?

To understand what is your immune system and what you should know about it, it’s important to understand the functions and parts of the immune system. The human immune system is in charge of protecting the body from foreign substances, such as antigens and pathogens. The immune system uses antibodies to neutralize antigens. To understand how do antibodies work, it’s important to consider that antibodies have the ability o to latch on to antigens and stop them from entering cells to infect them. Our bodies are born with immunity, but building up antibodies throughout our life is key to staying healthy. To learn what is immunity, it’s important to consider that antibodies are only developed after an antigen is found, which is why vaccines work and why the body only gets sick from a specific infection once.

The immune body system has three immune system types, which are innate, adaptive, and passive. The innate system contributes to the immune system definition as it is the system the body is born with and includes the cough reflex and stomach acid. The adaptive system continues to develop as your body is introduced to more antigens and is made of immune cells and white blood cells. The passive system is what is given to you, such as a vaccine, to develop antibodies to antigens you haven’t experienced the disease with. To understand where is your immune system located, it's important to consider that the immune system is located everywhere throughout your body, including the lymphatic system, tonsils, spleen, and appendix, as some of the immune system locations. This helps us understand how does immunity work.

What is the Relation between Allergies and the Immune System?

The relationship between allergies and the immune system is directly linked to how does your immune system work. When the body is exposed to an allergen, the immune system reacts by creating a high amount of antibodies. The specific reaction and severity depend on the number of antibodies created. Allergic reactions caused by the immune system are hay fever, asthma, and hives. How the body responds to allergens helps us understand what is immune system.