30 Mesmerising Facts About Your Immune System

Your immune system. You hear that phrase a lot don’t you? You’re told ways to boost your immune system with super foods and vitamin supplements, and you’re told all about the dangers of a weakened immune system. But what does your immune system actually do? How does it work? Where is it? And how does it get broken?

It’s something that we all know that we have, but unlike say, our hearts and our lungs many people don’t know a whole lot about this vital system in the human body. So let’s put that right.

Today we’re going to take a journey into the weird and wonderful world of the immune system, and we’ll take a detour to look at some fascinating history while we’re at it. Buckle up there might be dragons!


1. The Immune System Is Our Valiant Protector

The human immune system is our knight in shining armor. It’s on duty 24 hours a day working to defend us from diseases and other harmful foreign bodies.

The system works by identifying harmful bacteria, viruses, fungi and parasites that have found their way inside, and then it sounds the alarm to rally the troops, gives them their orders and sends them out to destroy the invaders. Once immune cells hear the alarm, they activate and begin to manufacture chemicals which allow them to regulate their growth and behavior, to collaborate with and control other immune cells, and to direct those new recruits to the site of the battle.

2. We Haven’t Alway Known About The Immune System Or The Germs That It Protects Us From

While there is some evidence that the ancients had an inkling about germs and disease, it took the emergence of Germ Theory in the 19th century before we mostly got it all figured out. For the longest time, people and their physicians had believed that bad air and fluid imbalances caused diseases.

Prior to the arrival of Germ Theory another mode of thinking about disease dominated Western medical circles. Humorism held that the human body is largely made up of four liquids or humors. Blood, yellow bile, black bile and phlegm. And that it was the surplus or deficiency of one or more of these humors that caused disease and disability. This led to treatment options like bloodletting (by cutting or leeches) in an attempt to restore the optimal balance.

Here are the top immune system boosting products out on the market right now.

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It’s hardly surprising given the ineffectiveness of such mainstream treatments that many people sought illicit alternatives in the form of concoctions brewed by their local wise women.

The Ancient Romans had a germ theory of disease that was for some inexplicable reason later forgotten. Roman scholar Marcus Terentius Varro (116-27 B.C.) wrote that,

“Precautions must also be taken in the neighborhood of swamps because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases.”

In 1546 an Italian physician Girolamo Fracastoro proposed that diseases were the work of seed-like entities that transmitted infection through contact, or through the air.

In 1720, the English botanist Richard Bradley who researched extensively into the plague, theorized that plague and ‘all pestilential distempers’ were caused by ‘poisonous insects’, which were only viewable with the help of powerful microscopes.

By the late 1850s the work of Louis Pasteur and Robert Koch provided convincing proof of the existence of bacteria and eventually in the 1890’s viruses were discovered.

There was a competing theory of disease around at the same time that Pasteur put forward his Germ Theory and that was the Terrain Theory of disease. This theory was initiated by Claude Bernard (1813-1878), and further developed by Antoine Bechamp (1816-1908). This theory proposed that the “terrain” or state of the body determined our state of health. When the body is functioning as it should, with both the immune system and detoxification systems working well, then there is a healthy terrain which means that the body can handle the various pathogenic microorganisms without becoming sick.

Germ Theory however, was firm in its stance that certain bacteria and viruses once encountered would always lead to disease. This was the thinking that underpinned the practise of vaccination. Vaccinate everyone so that the germs can never cause an illness.

Proponents of the Terrain Theory advocated keeping the body well nourished and strong and held the belief that a healthy body would not be fertile ground for disease to take hold. Which sounds remarkably like the advice that has become common knowledge in recent years.

3. The Earliest Known Reference To Immunity Goes Back Over Two Thousand Years


The first vaccine was developed in the late 18th century, but people had recognized that exposure to a disease offered future protection from that disease long before that.

In 430 B.C. the Greeks realized that people who had survived smallpox didn’t contract the disease a second time. These survivors were often called upon to nurse those afflicted with smallpox.

In 10th century China, healers began blowing dried and ground smallpox scabs into the noses of healthy patients. These people then contracted a mild form of the disease and once they had recovered, they became immune to smallpox infection in the future. This practice was called variolation.

4 Variolation Was Introduced To Europe By Chance

In 1721, Lady Mary Wortley Montagu imported variolation to Britain after observing the practise in Istanbul.

In 1715, she’d suffered from an episode of smallpox, which severely disfigured her face. Her 20-year-old brother died of the illness 18 months later. In 1717, her husband, was appointed ambassador to the Ottoman Court.

A few weeks after their arrival in Istanbul, Lady Montague wrote to her friend about the method of variolation in use there. A few years later she ordered the embassy surgeon to carry out variolation on her 5-year-old son, and upon their return to London in 1721, she had her 4-year-old daughter undergo the procedure in the presence of physicians of the royal court.

After some further trials on prisoners, who were offered a pardon if they survived (and they did), and the successful variolation of the two daughters of the Prince of Wales, this form of protection against smallpox became widespread.

The practise was not without risks however, and it wasn’t always effective. Two to three percent of the people who underwent the procedure died from the infection or became the source of further outbreaks. But the death rate from variolation was much lower than that caused by naturally transmitted smallpox.

The variolation procedure made its way to the Colonies, and its use became fairly widespread under the guidance of Rev. Cotton Mather. When an outbreak of smallpox occurred in Boston (carried on a ship from the West Indies), Mather recommended immediate variolation treatments, but the outbreak worsened and suspicions over the procedure grew. At the height of the epidemic, which saw half of Boston’s 12,000 population infected with the disease, a bomb was thrown at Mather’s house.

But when all was said and done and the mortality rates were calculated, only 2% of those who underwent variolation had succumbed to the disease, compared to 14% in the untreated population.

5. Immunity Changed The Course Of History

The practise of variolation played a role in the American War Of Independence. In 1766, American troops under the command of George Washington were unable to take Quebec from the British. A smallpox epidemic had reduced the ranks of Washington’s troops, but the British soldiers were at full strength because they had undergone variolation.  By 1777, Washington had learned his lesson and all his soldiers were variolated before beginning new military operations. Something to remember on the next 4th of July.

6. Edward Jenner Discovered A Safer Form Of Smallpox Inoculation

In 1796 Edward Jenner made the first step in the long process that ended with the eradication of smallpox from the face of the earth. For many years, he had heard tales of dairymaids that were protected from smallpox naturally after having suffered from cowpox. After giving this some thought Jenner concluded that cowpox not only protected against smallpox but that it also could be transmitted from one person to another to offer a mechanism of protection. In May 1796, he  found a dairymaid who had fresh cowpox lesions on her hands and arms. Using matter from her lesions, he inoculated an 8-year-old boy, James Phipps. James developed a mild fever and discomfort in his armpits. Nine days after the procedure he felt cold and had no appetite, but on the next day he was feeling better and made a full recovery. In July 1796, Jenner inoculated the boy with matter from a fresh smallpox lesion. No disease developed, and Jenner concluded that the cowpox protection was a success.

His discovery was initially rejected by the Royal Society but in time the method became accepted and the name that he gave to his process stays with us today.

He called his process Vaccination. The word derived from the latin for cowpox – vaccinia.

7. The Immune System Isn’t One Thing

The immune system is a network of cells, tissues, and organs that work in harmony to identify and destroy foreign invaders. These invaders are organisms such as bacteria, viruses, parasites, and fungi that can cause disease in susceptible individuals.

This system is incredibly complex. it’s able to recognize and remember millions of different hostile organisms and to produce the necessary secretions and cells to match up with and destroy the vast majority of them.

The immune system manufactures antibodies, proteins, white blood cells and other chemicals that recognize and attack anything that they identify as foreign to the body.

8. The Tonsils And The Thymus Gland Are Responsible For Making Antibodies.

Your tonsils aren’t those useless things that doctors love to yank out after all. They’re able to manufacture specific antibodies against germs in your mouth. So they’re your first line of defense against pathogens in the air and in food.

While your thymus gland trains and develops your T-cells to maturity.

9. Lymph Nodes Trap the Bad Guys

The lymph nodes and the lymphatic system carry lymph fluid, nutrients, and waste materials between the body tissues and the bloodstream. The lymph nodes filter lymph fluid as it flows through them and trap and hold onto any bacteria, viruses, and other foreign substances they find, which are then destroyed by a type of white blood cell called a lymphocyte.

10. The Spleen Is The Largest Lymphatic Organ In The Body

The spleen is a fist sized organ just to the left of the stomach. As an important part of the immune system it is responsible for filtering blood and removing old and damaged blood cells. Platelets and white blood cells are also stored there. The spleen has the ability launch an immediate attack on infectious microbes and to trigger a further adaptive immune response that calls into action the cells that recognize a particular infectious agent.

11. Your Bones Are Part Of Your Immune System

Bone marrow is another part of the immune system and it makes up 4% of your total body mass.

Bone marrow is a soft, flexible tissue that is found inside your bones. It’s mainly found inside the pelvic bones, the vertebrae and the long bones in your legs and arms and is made up of red marrow and yellow marrow.

The red marrow is mainly found in the pelvis, sternum, cranium (skull), ribs, vertebrae and scapulae (shoulder blade), and in the spongy material at the ends of long bones in the arms and legs. It’s responsible for producing red and white blood cells and platelets.

The process that produces red blood cells is called hematopoiesis, and this process produces an astonishing 500 billion blood cells per day.

Yellow bone marrow is found in the hollow interior of the middle portion of short bones. The yellow marrow contains fat and connective tissues and produces some of the disease fighting white blood cells. In cases of severe blood loss, the body is able to convert yellow marrow back to red bone marrow to increase red blood cell production.

When we’re born all of our bone marrow is the red kind and as we age more of it becomes the yellow kind. Only around half of adult bone marrow is red.


12. White Blood Cells Seek And Destroy

See those uglies in the image above? Those are bacteria and your white blood cells will kill them for you.

The white blood cells that are made in the bone marrow protect the body against infection. When an infection develops, white blood cells attack and destroy the bacteria, virus, or other organism responsible for the infection. There are several types of white blood cells which are broadly known as  Leukocytes and Lymphocytes.

There are three types of lymphocytes. B-cells, which make antibodies that attack bacteria and toxins, T-cells, which help to destroy infected or mutated (cancerous) cells and Natural Killer cells. T-cells mature in the thymus gland.

Leukocytes are white blood cells that identify and eliminate pathogens.

13. White Blood Cells Only Make Up A Fraction Of Your Blood

Given the vital role that white blood cells play in our health, you might think that we have masses and masses of them.

In Fact they only make up 1% of the cells in the 8 pints of blood in an adult’s body. But don’t worry, that’s more than enough, and we actually have between 5,000 and 10,000 white blood cells standing guard in each microliter of blood. A microliter is one millionth of a liter. And the 8 pints of blood in our bodies translates to about 5.6 liters. So that works out to between 25,200,000,000 and 56,000,000,000 white blood cells. Phew!

14. Sometimes You Feel Sick Because The Immune System Is Doing Its Job

Your bodies response to infection leads to the symptoms that we associate with certain conditions. While you might think that it’s the viruses, bacteria and fungi and that are making you feel lousy, it’s actually your immune system reacting to the microbes that is behind it all.

Take the common cold as an example. When the rhinovirus (responsible for the common cold) invades the cells that line your upper respiratory tract, immune system chemicals called histamines dilate (expand) your blood vessels and increase their permeability. This allows proteins and white blood cells to more easily reach the infected tissues. But this expansion of the blood vessels narrows the space available in your sinuses and nasal cavity and leads to congestion.

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Then because of increased fluid leakage from your now more permeable capillaries, combined with an increase in mucus production triggered by histamines you have more ‘snot’ in your system that needs to get out. When the congestion is at its worst all of this mucus builds up and leads to uncomfortable pressure, and when the congestion begins to subside you get a runny nose.

15. Lack Of Sleep Hurts Your Immune System

Research over the past few decades has consistently shown that sleep deprivation compromises the immune system’s disease-fighting abilities.  When you don’t get enough sleep, your body produces fewer white blood cells. Even a single night of disturbed sleep can impair the immune system.

A 2012 study even found that vaccines may be less effective for people who sleep less than six hours a night because the loss of sleep leads to a sluggish immune system response.

16. Your Immune System Can Attack You

Your Immune System Can Attack You

For some people their immune system is the source of their debilitating diseases. In these cases the body’s natural defenses become over sensitive and attack normal tissues as if they were foreign bodies. These diseases are known as autoimmune diseases and include Addison’s disease, Celiac disease, Crohn’s disease, Endometriosis, Fibromyalgia, Hashimoto’s Thyroiditis, Lupus, Multiple Sclerosis, Psoriasis, Rheumatoid Arthritis and Ulcerative Colitis.

17. Autoimmune Diseases Mostly Affect Women

Autoimmune disorders don’t affect men and women equally. Approximately five to eight percent of the U.S. population has an autoimmune disease and about seventy eight percent of those people are women.

18. A Huge Part Of Your Defenses Come From Bacteria

In addition to all of the defences that your body produces, the bacteria that colonize your gut help to protect you too.

The human body is home to trillions of bacteria. We’re more bacteria that we are human. The bacteria in our bodies outnumber our own cells 10 to 1.

In the gastrointestinal tract, we depend on these helpful microbes to help with digestion and with the manufacture of vitamins B and K.

Research has also shown that the friendly bacteria in our guts helps our immune system. These bacteria stop pathogenic bacteria from taking root in our tissues and they also train the immune system so that it can better distinguish between disease causing pathogens and harmless bacteria.

The good bacteria also influences the immune system’s sensitivity to antigens. An antigen is anything that has the potential to initiate an antibody response, like microbes, and sometimes the body’s own tissues.

These beneficial bacteria can help the immune system to recognize what is and what isn’t an antigen and potentially help to prevent autoimmune diseases.

The bacteria also produce their own useful antibodies and trigger the production of intestinal proteins, which allow the immune system to repair internal injuries.

19. When You Take Antibiotics…

You don’t only kill the pathogenic bacteria. You kill huge amounts of the beneficial bacteria too. That’s why it’s a good idea to take prebiotics and probiotics whenever you have to take antibiotics. These help to repopulate your gut with the bacteria that you need to be well.

20. Sometimes Those Good Bacteria Have to Be Transferred Another Way (!)

In cases where the immune system is severely compromised and serious infections that will not respond to antibiotics have become life threatening, beneficial bacteria from a donor is transferred to the sick individual.

After multiple rounds of antibiotics the good gut bacteria that are vital to an effective immune response are wiped out, leaving the person suffering from infection incredibly vulnerable, not only to the ravages of the initial disease but also to opportunistic infections.

One treatment that is offered in these cases is a fecal transplant. This procedure takes good bacteria from the gut of a healthy person via the stool and mixes it with saline. It’s then strained and transferred to the colon of the patient using a colonoscopy, endoscopy or an enema.

Fecal transplant has a 91% success rate against clostridium difficile and they’re also used to treat autoimmune conditions.

21. Sunlight Has Good And Bad Effects On The Immune System

The ultraviolet (UV) radiation in sunlight can suppress the immune system’s response to microbial infections. And it doesn’t take a lot of sunlight to do it! To suppress the human immune system, it takes UV doses that are much less than those required to cause barely detectable sunburn.

But at the same time sunlight stimulates the production of vitamin D in the skin. A recent study has suggested that T-cells don’t mobilize if there aren’t sufficient levels of vitamin D in the bloodstream. Other research has found that vitamin D might stimulate the production of antimicrobial substances in the skin and these compounds help defend the body against new infections.

22. Sunlight Helps To Alleviate Stress And Depression

And both of these conditions depress the immune system. People who suffer from chronic levels of stress and depression get sick more often than people who are relaxed and happy.

23. We Have Two Kinds Of Immunity

Innate Immunity and Adaptive Immunity. The innate immune system consists of cells and proteins that are always ready to fight any pathogen to provide immediate defense against infection.

Adaptive immunity occurs after an initial response to a specific pathogen and creates immunological memory. This  leads to a fast response to subsequent encounters with that pathogen. Acquired immunity is the basis of vaccination.

Adaptive immunity can provide lifelong protection in some cases. Someone who recovers from measles for example will be protected against measles for life, but someone who contracts chickenpox can get it again.


24. Starfish Show How Ancient Innate Immunity Is

Invertebrates usually lack the adaptive immunity that vertebrates have. But they do have innate immunity. This was discovered when a Russian biologist pierced a starfish larva with a rose thorn. Upon examination the next day he discovered a multitude of tiny cells trying to engulf the thorn, which is an innate immune process called phagocytosis.

The starfish has remained largely unchanged for some 500 million years which suggests that the innate immune system has very ancient roots.

25. It’s the Adaptive Immune System that’s To Blame For Your Allergies

Sometimes the adaptive system makes a mistake and is unable to distinguish harmful foreign substances from harmless ones. The effects of this are hayfever, asthma and other allergies.

26. Being Too Clean Can Prevent The Immune System From Developing Properly

It’s tempting to be a clean freak, especially when you’ve got children crawling around and testing the world with their fingers and their mouths. But spraying and scrubbing with disinfectants can kill off too many foreign pathogens (good and bad) and leave the immune system without the chance to encounter them. The immune system needs to learn and without a steady stream of microbes to practise on it won’t graduate with honors.

Kids that get to play in the dirt are often the ones that have the most disease resistance and they tend to suffer from fewer allergies.

A great way to let your kids play in the dirt is to have them help you to grow a garden. Dirt, fresh air and nutritious food make a great combination for raising healthy kids.

27. Smokers Have Weaker Immune Systems

The good news for smokers is that once you give up the smokes, your immune system will rebound and start to pick up strength. In just one month after quitting you will have more immune cells and lower levels of cortisol, a stress hormone. Less stress hormones equal a stronger immune system.

28. Sometimes Your Immune Response Goes Into Overdrive And This Can Kill You

A Cytokine Storm is a potentially fatal immune system reaction. When the immune system is fighting harmful microbes, cytokines signal to the immune cells and tell them where to go. In addition, cytokines activate a mechanism in the immune cells which stimulates the production of more cytokines.  Normally, the body keeps this feedback loop in check but sometimes this reaction gets out of control and too many immune cells are activated in a single place. Cytokine storms can do significant damage to body tissues and organs. If a cytokine storm occurs in the lungs, for example, fluids and immune cells accumulate and eventually block off the airways.

Cytokine storm occurs in the terminal phase of ebola infection. The immune system attacks every organ in the body and bursts blood vessels which make the infected person bleed both internally and externally. One of the keys to preventing death in ebola patients is preventing this cytokine storm from happening.

With ebola the virus itself doesn’t kill you, the cytokine storm unleashed by your immune system does.

29. Some Substances Can Help Your Immune System to Heal You

There are some truly amazing natural plant substances which have remarkable effects on the immune system. These are called Adaptogens and as the name suggests taking these substances allows your immune system to better adapt to the disease condition that it is trying to cure.

A well known Adaptogen is Ginseng, but there are plenty of others.

Adaptogens stimulate your body into producing more of a specific type of white blood cells. Macrophages (macro=big, phage=eater) are white blood cells that destroy pathogens. They live in the mucus membranes of the body but are also present in internal organs. They are our first line of defense and protect us from colds, flu and other types of infection.

Adaptogens can also work to support the bone marrow which is where the macrophages and other immune cells are made.

They also boost immunity by supporting and balancing the endocrine system, and research has shown that they support adrenal functions, The adrenals are our stress glands and when they are weakened we experience fatigue and suppressed immunity.

30. Your Immune System is the Ultimate Hacker

Your body has the ability to make endless random variations of antibodies until it finds one that will kill off the invading pathogen. It’s an approach that is similar to the brute force hacking that’s used to break passwords and encryption, where gazillions of combinations are tried out every second.

Once the correct antibody has been found your immune system ramps up production and sends them out to save the day. A definite White Hat Hacker.

And on that note, we’re safely home, you can unbuckle your seat belt and go and stretch your legs. Thank goodness we didn’t encounter any dragons!