Most people are not very familiar with the functions of the immune system. However, ever since insects evolved, there has been some form of immunity that has a flexible response to various infectious agents and other environmental irritants.
In this article, you will learn some immune system facts related to both parts of immunity — innate and acquired (adaptive) — which interact together and exchange information continuously to keep us protected.
Furthermore, we displayed for you the most relevant statistics on the common immunity-related diseases, and, to fresh it up, we punched in with some seriously fun facts about the immune system.
The Top 10 Immune System Statistics
- Humans have between 4,500 and 11,000 white blood cells in each microliter of blood
- Hundreds of millions of different B cells circulate in the body
- Cytotoxic immune cells are involved in both anti-infectious and anti-tumor immunity
- Dendritic cells are the most powerful antigen-presenting cells
- There are about 600 lymph nodes in the body
- Disease symptoms may represent the immune system doing its job, according to immune system statistics
- Asthma affects over 330 million people globally
- May 10 is regarded as World Lupus Day
- Antibodies from one person can be used to stimulate the immune system of another
- Fever is a positive indication that the immune system is active
Now that you have read some of the facts and stats cherry-picked from the article, it’s time to dig deeper. Below you’ll find a ton of useful information regarding the immune system and more stats and facts to expand your knowledge. Enjoy!
Facts About the Immune System and its Cells
Ever wondered why you feel feverish today, and you are kicking and moving around the following day? It’s the fantastic cells of your body’s immune system. These cells work their heads off to make sure you are always on the go! These cells form the military base of the body.
Each day, you get exposed to millions of bacteria and offending foreign agents, and you don’t notice because your body’s immune cells are doing a great job. So you should be asking, what is the immune system? Let’s check out some immune system facts.
1. Humans have between 4,500 and 11,000 white blood cells in each microliter of blood.
The average number of white blood cells — which are mainly immune cells — depends on age and sex. However, the number of these cells can be lowered or elevated as a result of various diseases, making the complete blood count testing a routine investigation.
2. Most of the immune cells reside in tissues and not in the blood.
Besides the central immune organs such as the thymus and bone marrow (where the immune cells come from and become immunocompetent), most of the immune cells are widespread in the peripheral immune system parts. These include lymph nodes, spleen, liver, mucosa of digestive and respiratory systems, skin, etc. Consequently, they can detect, react, and eliminate every pathogen that they encounter, ensuring a robust immune system defense.
3. About 98% of thymocytes die in the thymus during a process called negative selection.
The majority of future T lymphocytes, or the so-called thymocytes, fail during the development processes and die. Only the remaining 2% survive and leave the thymus as T cells, which can become immunocompetent. This is undoubtedly one of the most interesting facts about the immune system.
4. Hundreds of millions of different B cells circulate in the body.
The reason for this seemingly large number is the biological requirement of our body to recognize every single pathogen. Each B cell produces a unique antibody that is specific to a particular unknown or dangerous molecule.
5. The immune system is broadly divided into the innate and the adaptive immune system.
The immune system can be seen as a collection of cells, tissues, and organs that work together to prevent foreign agents from harming body organs. However, articles on immune system definition have shown that there is no universal definition.
These two divisions of the immune system use self to non-self discrimination to fight off pathogens. Together, they provide the best defense against offending agents.
6. Cytotoxic immune cells are involved in both anti-infectious and anti-tumor immunity.
These cells are cytotoxic immune cells and natural killer cells (NK cells), representing specific and nonspecific immunity, respectively. By killing virus-infected or tumor-host cells, they seek to limit the complications of pathological processes.
7. The innate immune system provides the first point of defense against offending agents.
The innate immune system is like the local police and is always available and ready to respond to foreign invaders in the body. This is one of the fun innate immunity facts .
The cells of the innate immune system function via three major processes: recognition of the offending agents, activation of defense mechanisms, and subsequently, elimination of the offending agents.
8. There are several cells that constitute innate immunity.
These cells include epithelial cells, neutrophils, macrophages, dendritic cells, natural killer (NK) cells, and the complement system of proteins
Epithelial cells generally form the lining of many organs. They also secrete immunological molecules such as defensins to aid in warding off offending agents.
Immune system facts reveal that the dendritic cells serve as antigen-presenting cells and deliver antigens to T-lymphocytes.
Neutrophils and macrophages act as phagocytes, natural killer cells are especially helpful in fighting against viral agents, and the complement proteins act as phagocytic agents and opsonins.
9. The adaptive immune system provides a more specialized and specific form of immunity.
Offending agents and bacteria cannot differentiate between specific vs nonspecific immunity and are usually caught aback when they encounter the adaptive immune cells.
The immune system can be divided into two major groups: humoral immunity and cell-mediated immunity.
Humoral immunity consists chiefly of B lymphocytes and is responsible for protecting the body from extracellular microbes (bacteria).
Cell-mediated immunity comprises chiefly T lymphocytes and is responsible for protecting the body against intracellular microbes (viruses). This is one of the essential adaptive immune system facts.
10. The only cells in the body with the ability to produce antibodies are the B lymphocytes.
B lymphocytes develop and mature in the bone marrow (unlike T cells that mature in the thymus) and are eventually sent to the peripheral circulation.
These lymphocytes in the peripheral circulation, when activated, change from their inactive form into active plasma cells, releasing antibodies.
11. Class I Major Histocompatibility Complex (MHC) molecules are expressed on all cells with a nucleus.
The MHC molecules function to display antigens so they can be recognized by antigen-presenting cells. The human MHC molecules are called human leukocyte antigens.
One of the interesting adaptive immune system facts is that the Class I MHC molecules are encoded by three genes: HLA-A, HLA-B, and HLA-C and are recognized by cytotoxic T cells.
12. Class II MHC molecules are expressed on cells that present phagocytosed antigens.
(British Society for Immunology)
Class II MHC molecules have a binding site for the helper T cells, making it possible for the CD4 cells to recognize the antigens presented by the Class II MHCs.
The Class II MHC molecules are encoded in the HLA-D region comprising three subregions: HLA-DP, HLA-DQ, and HLA-DR.
13. Dendritic cells are the most powerful antigen-presenting cells.
(British Society for Immunology)
This is one of the innate immunity facts that are worth knowing. Antigen-presenting cells (APCs) are immune system cells, which, as the name implies, are responsible for presenting antigens to T cells.
The antigen-presenting cells present these antigens via the help of the MHCs. It is these MHCs that the T cells first recognize and can respond to the antigens. As a result, the T cells are said to be MHC restricted. The cytotoxic T cells are Class I MHC restricted, and the helper T cells are Class II MHC restricted.
Facts About Immune System Organs
The immune system comprises organs, tissues, and cells that work in a highly coordinated manner to eliminate offending agents.
The following facts will enlighten you on the organs that make up the immune system.
14. The lymph node is the principal meeting place of the immune system and antigens.
Independently from where the pathogen enters the body, usually, it’s delivered to the regional lymph nodes, where T and B lymphocytes reside, waiting for danger signals.
15. You can live without the spleen.
Situated just above the stomach in the left hypogastric region, between the 9th to 12th ribs, the spleen is a major immune system organ that plays a significant role in taking care of blood-borne antigens. However, immune system 2020 facts reveal that you can survive without the spleen because the liver can take over the main immunologic functions of the spleen.
Nevertheless, if you are without a spleen, you can be prone to infections by encapsulated bacteria such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. The spleen is the principal organ for handling encapsulated bacteria, and when the spleen is removed, the liver cannot take over this function.
16. The T and B lymphocytes have a particular pattern of arrangement within the peripheral lymphoid organs.
In the lymph node, the B lymphocytes are located in the follicles (but migrate to the germinal center when activated), and the T lymphocytes are located adjacent to the follicles, within the paracortex.
In the spleen, the B lymphocytes are also located within the follicles, but the T lymphocytes are concentrated within periarteriolar lymphoid sheaths.
17. There are about 600 lymph nodes in the body.
(Medical News Today)
These lymph nodes are responsible for filtering lymph from the circulation to eliminate microbes and toxins. Immune system statistics in 2021 show that as lymph circulates through the lymph nodes, these bean-shaped organs can mop up microbial antigens presented to them by antigen-presenting cells.
18. The thymus shrinks by about 3% yearly throughout middle age.
In the process called involution, the thymus is replaced with fat tissues after puberty. This is one of the most interesting thymus facts, showing that in older people, the expansion and regeneration of T cells play a role more significant than their production.
19. The spleen provides crucial support in antigen presentation to the immune cells.
Besides its other roles in the function of the immune system, important facts reveal that the spleen also aids hematopoiesis and red blood cell clearance, thus regulating the T and B cell response.
Although you can live without a spleen, it was shown that surgical splenectomy due to trauma or diseases leads to severe dysregulation in immune functions to pathogens.
Since the immune responses to encapsulated bacteria are the most altered, splenectomized people are more prone to meningitis and sepsis. People who don’t have a spleen should take additional conjugated vaccines against specific pathogens.
20. The organs of the lymphoid system are divided into primary and secondary lymphoid organs.
(University of Leeds: The Histology Guide)
The primary lymphoid organ comprises the thymus and the bone marrow. The thymus is the site where the T cells mature, and the bone marrow is the site of production of both the T cells and B cells both only the B cells mature there.
The secondary lymphoid organ comprises lymph nodes, the spleen, and the cutaneous and mucosal lymphoid tissues.
Statistics on Immune System Diseases
Diseases occure as a result of the body’s inability to cope with stressors or offending agents. When the immune system loses its efficacy, the body becomes prone to several diseases. However, an increased immunologic reaction which is more than normal can also lead to diseases.
Thus, immune system diseases can be due to a decline in the function of the immune system or an overreaction of the immune system.
The following facts about immunity will give you a detailed insight into immune system diseases.
21. Hypersensitivity reactions are due to an abnormal response of the immune system to an antigen.
There are four types of hypersensitivity reactions. Statistics reveal that these types explain the distinction in the pathogenesis of the mechanism behind how the immune response causes tissue damage.
Type I hypersensitivity reactions are typically allergic reactions and are due to the over-reaction of TH2 cells and IgE antibodies. Type II hypersensitivity reactions are antibody-mediated and are due to the over-reaction of IgG and IgM antibodies. Type III hypersensitivity reactions are due to immune complexes, and Type IV hypersensitivity reactions are cell-mediated and are due to the over-reaction of TH1 and TH17 cells.
22. Asthma is a type I hypersensitivity reaction and affects over 330 million people globally.
Immune system statistics in 2021 reveal that asthma occurs when the body responds abnormally to exogenous substances called allergens.
These allergens are naturally occurring in the environment and will not cause a response in normal individuals.
However, asthmatic individuals respond abnormally to these substances. Their antigen-presenting cells see these substances as harmful and activate the TH2 cells, which then secrete IgE that causes mast cell destabilization and release of histamines.
The histamines cause bronchoconstriction seen in asthmatic patients.
23. Autoimmune disorders affect about 5% of the United States population.
(National Stem Cell Foundation)
Autoimmune disorders is the third most common autoimmune disorder in the US. It occurs as a result of an immunologic reaction against self-antigens. What this means is that the body begins to attack its organs.
According to Important facts about the Immune system, autoimmune diseases occur due to a failure of immunologic tolerance. Immunologic tolerance is needed to eliminate self-reactive T cells from circulation.
24. May 10 is regarded as World Lupus Day.
(World Lupus Day)
Lupus is an umbrella term for systemic autoimmune reactions, principally affecting the skin, joints, and blood vessels.
Since 2004, lupus organizations worldwide have considered May 10 to raise awareness for Lupus and carry out activities that seek to educate the public about Lupus.
The aim is to make Lupus a global health priority and give individuals with Lupus a reason to smile, knowing that they can be treated effectively.
25. Systemic lupus erythematosus is the most common Lupus disease.
(Lupus Foundation of America)
According to immunity facts, about 70% of all diagnoses of Lupus cases are systemic lupus erythematosus (SLE). It is an autoimmune reaction caused by an abnormal immunologic response to nuclear antigens.
Though there are the diagnostic criteria for SLE, most individuals with this disease have a classical malar rash on the face, described as a butterfly rash. The pathogenesis is relatively complex and not well understood.
26. Rheumatoid arthritis, unlike osteoarthritis, is an immune-mediated condition.
Arthritis is simply the inflammation of joints. Differentiating between rheumatoid arthritis and osteoarthritis has been a really difficult task for patients with this condition for many years now. Some say, “I have arthritis.”
Rheumatoid arthritis is an autoimmune reaction caused by an abnormal response of T cells to citrullinated peptides (found in the joints), while osteoarthritis is due to degeneration of the articular cartilage of the joints.
Immune system facts in 2021 reveal that the clinical presentation of these two major arthritis disorders differs. Rheumatoid arthritis tends to cause pain that is relieved with activity, and the opposite is the case for osteoarthritis.
27. Autoimmune diseases tend to run in families with members of an extended family having more than one autoimmune disease.
(National Stem Cell Foundation)
Autoimmune diseases have a strong genetic link. The most implicated genes are the HLA genes, especially the HLA-D genes. There are also other non-HLA genes implicated in autoimmune diseases.
28. Disease symptoms may represent the immune system doing its job.
Signs such as fever and inflammation can be seen in several diseases. They are part of the normal physiology of the immune system and are usually good signs. However, the cytokine storm or the release of a vast quantity of immune mediators, which can also be a part of the inappropriate immune response, denotes a bad prognosis due to many complications, including multiorgan failure and death.
29. Autoimmune diseases are more common in women.
The immune system facts unconditionally showed that women are more prone to the development of an autoimmune disease, probably due to hormonal factors. The female to male ratio is 10:1 for Hashimoto’s thyroiditis, 9:1 for systemic lupus erythematosus, 9:1 for primary biliary cirrhosis, 2.5:1 for rheumatoid arthritis, 2:1 for multiple sclerosis, etc.
30. Allergies are an example of an overreaction of the immune system to harmless antigens.
The allergic reaction is a nonspecific response to a specific molecule, such as pollen or dander, which leads to the release of histamine and other mediators. They are associated with unpleasant allergy symptoms that vary from mild, such as sneezing, to severe ones, including death.
31. Оne in every 500 individuals is affected by a primary immunodeficiency.
According to the current immune system information, there are over 400 different primary immunodeficiencies (PIDs). They can be diagnosed at any age, from early childhood to adulthood. The clinical manifestation of PIDs could be followed by recurrent, severe, unusual, or difficult-to-treat infections. It‘s important to remember that PID patients are at risk of other complications, including the occurrence of autoimmunity and malignancies.
32. Sleep deprivation, lack of physical activity, and stress can weaken the immune system.
All of these factors are proven to deteriorate immune functions by different mechanisms. Moreover, chronic insomnia can influence the decline in white and red blood cell production.
Fun Facts About the Immune System
Did you know that in ancient times it was thought that the immune system never existed? The immune system has got its share of some hilarious stories behind it.
Relax and enjoy these interesting facts.
33. Fever is a positive indication that the immune system is active.
This may sound counterintuitive, but immune system important facts show that a fever is a sign that your immune cells are still in the mood.
Fever is a major sign of inflammation, and do you know what inflammation is? Inflammation is the response of living tissues to offending agents. And, of course, the cells involved here are your immune cells.
34. Stress has a negative effect on the immune system.
(The Physiology Society)
Do you know what happens when you’re stressed? Your adrenal cortex releases cortisol. Cortisol is called the stress hormone because it prepares your body for periods of stress via various metabolic processes. It increases glucose and amino acid concentration in the blood.
However, immune system facts for 2020 have revealed that cortisol is an immunosuppressant and can decrease the immune system’s efficacy. That is why individuals on long-term corticosteroid therapy are monitored for any incidence of infection.
35. Antibodies from one person can be used to stimulate the immune system of another.
Heard about passive immunization? Here, individuals are injected with already formed antibodies from another individual. This is usually done when the recipient’s immune system is too weak to produce its antibodies.
36. The body’s active immunity is stimulated by the presence of a pathogen.
Ever wondered what was in the vaccines that you get injected with? Immune system statistics in 2021 reveal that most of them contain pathogens that can be potentially harmful. However, they are injected in small quantities that are incapable of causing harm.
The immune system recognizes these pathogens and produces antibodies against them. This is the basis of active immunity.
37. The immune system can be trained.
The immune cells have been training since their nascence, first in the thymus, and then in the circulation and tissues by encountering different pathogens. However, vaccines are also a way to train immune cells by avoiding complications arising from a real infection.
38. Being too clean can increase your risk of getting an autoimmune or allergic disease.
According to the “hygiene hypothesis,” although washing and disinfecting hands is the best way to avoid infection, this may increase the incidence of autoimmune and allergic diseases, according to the immune system statistics and pathogens-associated infection reports. This is especially valid for Western countries, where minimizing the meeting of some pathogens leads to the development of immune diseases.
39. Laughter helps our immune system to manage stress.
Twenty minutes of laughing a day lead to the release of dopamine and other hormones, which make us feel better, decrease stress and help the immune system work properly. In such a way, laughter can be considered a non-specific defense mechanism.
40. How friendly and extroverted you are may depend on your immune system.
One of the most interesting immunity facts comes from a scientific study that shows that the immune system could play a role in controlling social behavior through the interferon-gamma (IFNγ) cytokine.
From an evolutionary perspective, the immune system may be activated to protect us from infections during socialization. This molecule can also be the link between immunity and neurological and psychiatric disorders, including autism.
41. As we get older, the immune system ages too.
The immune functions decline with aging, including dysfunction in the chemical barriers of innate immunity, adaptive immune cell activation, etc. This phenomenon explains why secondary immune deficiencies or autoimmune diseases may occur in older people.
How Food Impacts the Immune System Physiology
Ever heard of the statement, “You are what you eat”? This also applies to the immune system. A diet fortified with fruits and vegetables will surely make your immune cells smile, but a diet of junk will only mean trouble for your immune cells.
Wondering how to boost your immune system? Then eat well.
The following facts will enlighten you on how food affects the immune system.
42. Vitamin D is a hormone that modulates immune functions.
Since deficiency and insufficiency in vitamin D are associated with susceptibility to infections, autoimmunity, or other problems, getting sufficient amounts of vitamin D through food and supplements can boost the immune system. It can also prevent many other complications associated with bone homeostasis.
43. A healthy diet with sufficient quantities of protein supports humoral immunity.
A balanced diet is essential for well-being and maintaining a healthy immune system. Getting enough protein will help you fight off infections, particularly through the proper production of antibodies. The scientific facts about the immune system confirm that poor nutrition and some diets may lead to immune dysfunction that can alter humoral immunity, including a lack of flu-shot antibodies or other antibodies after vaccination.
44. Zinc is an essential micronutrient for cell-mediated immunity.
Many conditions, such as growth retardation, cognitive impairment, and immune dysfunctions, are attributed to zinc deficiency; thus, it makes sense to supplement it in the case of lower levels in the body. Some of the best foods to boost the immune system by increasing zinc consumption are meat, shellfish, legumes, nuts, dairy products, eggs, and whole grains.
Why is the immune system important?
The immune system provides all the protective mechanisms needed to fight off infections or other dangerous agents. It helps us clear the dead microorganisms after treatment, toxins, etc. Without the immune system, we wouldn’t be able to survive, not only because of the pathogens (viruses, bacteria, fungi, etc.) around us but also because the immune system is involved in the protection of tumor cells.
How does the immune system work?
The immune system works on many levels and through different mechanisms. First, the antigen is welcomed by the innate cells, which are responsible for the initial immune response and presentation to lymphocytes. T and B cells then recognize the antigen and activate, leading to the creation of specific immunity and the production of antibodies. Some of the activated T and B cells remain as memory cells, ready for rapid activation upon re-encounter with the same antigen.
Do flu shots weaken the immune system?
No, neither flu shots nor other vaccines weaken your immune system. The principle of vaccinations is to prepare the immune system for the possible encounter with pathogens. A real infection (flu, morbilli) leads to an immune system that could be weak for months. Furthermore, vaccinated people may also get the flu, but the infection is milder.
Regardless of the disadvantages of the immune system, such as being extremely energetically expensive or needing to be tuned to avoid the overreaction and development of immune-mediated conditions, the protection that it ensures is necessary to sustain life. The immune system facts can help us realize the essential role of our immune system in safeguarding our body.
- BioMed Central
- British Society for Immunology
- Cleveland clinic
- Lupus Foundation of America
- Mayo Clinic
- Medical News Today
- National Stem Cell Foundation
- National Stem Cell Foundation
- PubMed Central
- Science direct
- Sleep foundation
- World Lupus Day
- University of Leeds: The Histology Guide