An Overview of the Human Immune System
The immune system is a complex and multi-organ system. It’s a complex organization that we don’t fully understand. Both disease-specific and general research have dramatically increased the human understanding of the system, including the various types of cells and pathways that trigger the body’s defenses. Still, we don’t know all of the reasons why it sometimes turns on itself, causing autoimmune diseases.
Below is an overview of the immune system and what does in our body, from head to toe.
The First Line of Defense
… Or, more accurately, from skin to bone. The first line of defense that our bodies have against infection is our skin. Layers of dead cells coated with oils and enzymes from sebaceous glands act as a barrier between us and the outside world. There are also bacteria, yeasts, and even viruses on our skin that keep less-welcome microorganisms from taking residence, protecting us further.
Our eyes, mouth, nose, anus, and genitals act like gateways for pathogens to get through this protective layer, but there are gatekeepers:
- Tears wash out the eyes and contain salts, water, and antimicrobial enzymes that keep them clean
- Mucous in the nose catch small particles and pathogens and helps the nose and lungs remove them (either out of the body, through coughs and sneezes or into the stomach, by swallowing)
- Stomach acid destroys swallowed pathogens
- Saliva and mouth-based bacteria have some anti-microbial properties
We actually all have bacteria, viruses, and other microorganisms living inside us that help prevent infection. They help by taking resources away from potential pathogens and by creating anti-microbial chemicals that protect the body. Many of the bacteria living in our guts also help digest certain foods and provide vitamins essential to our health. The gut is very important to the immune system, and you can read more about it here.
This is why hygiene is so important to health. Cleaning your skin (baths, showers, and hand-washing) and your mouth (brushing teeth) wash away a lot of pathogenic bacteria.
When pathogens do get through these defenses, they make their way into other organs or the bloodstream. This is when immune system is supposed to take action.
The Inflammatory Response
Alongside our first-line defenses, our immune system has something called innate immunity. Innate immunity is our baseline ability to defeat invading microorganisms, even when we’ve never experienced them before.
This is usually a general and intense response. It is a part of the reason why people get sicker the first time they catch an illness.
High fevers, a runny nose, rashes, and other symptoms of sickness are the body putting forth a powerful and general inflammatory response. As the body experiences more diseases and builds up a repertoire of antibodies (that recognize the illness) it is better able to modulate its responses and fight illness more efficiently. This is called the “adaptive immune response.” Adaptive immunity involves T cells and B cells that specifically target the pathogen or the affected cells.
Put another way, when the body doesn’t recognize a pathogen, it mounts a generic, powerful response. But, when the body does recognize the invading pathogens, it responds by creating strategic antibodies designed to combat the specific threat.
The inflammatory response is a chain reaction of activity in the body that leads to an appropriate (or inappropriate) response to a pathogen. Fighting infection is a long and complex process, but in short it involves:
- Antibodies patrolling the body recognize a pathogen or the skin or cells in muscle tissue are damaged. In either case, inflammatory particles are then released into the surrounding tissue.
- These inflammatory particles – of which there are too many to name in a brief overview – affect the cells around them. The cells respond by causing them to release more inflammatory particles.
- What happens next depends on the particular particles and the damage involved, but eventually these inflammatory particles act as an alarm signal, triggering the immune system to act.
- Other cells, such as lymphocytes, are sent to the area.
- Fluid is often retained around the cells in the area, causing swelling.
- Cells in the disturbed area may be triggered to produce more heat, creating a “fever.”
- Blood vessels are expanded to allow the passage of immune system cells, reddening and warming the area.
- Exactly what happens depends on the injury and the signaling particles that get released
- In all cases, the body is set to a higher alert level overall, and more immune cells end up in circulation. These immune cells can activate in response to other pathogens or injuries.
- After the threat is no longer detected by the body, the immune system ramps down the inflammatory response. Again, the signals involved depend on the response, but usually, the body returns to normal.
The Body’s Reaction
The body’s reaction, and thus the specifics of the immune response, vary depending on what the body is fighting. When it’s a virus, T-cells are deployed, and cause the infected cells to destroy themselves. When it’s a wound or an irritant on the skin, platelets and regeneration-inducing immune system particles are sent to the area to fight off any invaders while the skin heals. If there is a bacterial infection, the whole body will turn up the heat production to “cook” the bacteria – as in a fever.
The body figures out the correct response to a situation because it is built into the immune response. Or because it ‘learns’ the way that it is supposed to handle a pathogen or signal. This learning process is called “immunization.” Although we know parts of it, other aspects of it are unclear because of the complexity of the system. The body becomes immunized when it is exposed to a pathogen or substance. Vaccines immunize the body by exposing it to a less potent version of a disease or to the antigens that would be found in the disease. But it can happen naturally as well.
Instead of resetting completely, it saves antibodies of particular pathogens to a sort of library. This allows the body to recognize and be better able to fight off infections. This is why second or third infections from the same source are less intense.
However, this is also how many allergies work. When the body develops antibodies to harmless and common substances, it marks them for attack and triggers an inappropriate inflammatory response. It is this inflammatory response that causes the damage and danger associated with allergies.
Autoimmune diseases are similar. In both cases, they are treated by medications that modulate the immune system.
Where do immune system cells come from?
There are many different types of immune system cells, but most come from the same place that our red blood cells come from: our bone marrow. Bone marrow is a region of soft tissue in the center of certain bones including:
- the sternum
- spinal vertebrae
- iliac bones (in the pelvis)
- shoulder blades
Colloquially, many different types of immune system cells are called “white blood cells.” They are also known as leucocytes. These blobby cells prowl through both blood vessels and lymphatic vessels, seeking out pathogens.
There are many different types of white blood cells that are specialized for specific activities. Neutrophils tend to attack bacteria, while macrophages generally stick to patrolling for pathogens and cleaning up dead cells. Many, however, are more generalized. White blood cells can be found in lymphoid organs like the thymus and spleen, and will also be in the bone marrow and the lymph nodes.
Lymphocytes also are produced in the bone marrow. And often stay in the bone marrow (B-lymphocytes,) where they act as the memory of the immune system. B-Lymphocytes produce antibodies that recognize pathogens and alert the body to invasion. When lymphocytes travel to the thymus, they are stored and become T-lymphocytes. They patrol the bloodstream, seek out marked cells, destroy them, and alert the rest of the immune system to their presence.
Antibodies are produced by leucocytes and lymphocytes, and act as both marker and destroyer, depending on the type. These remain present in the body as a part of the memory of the body. They are major factors in adaptive immunity – our body’s “trained” response to pathogens. Antibodies have one end, which is variable, and fits like a puzzle piece to proteins on the surface of pathogen cells. Or on the surface of the body’s cells infected with a virus. Once it does, the signal and marker molecules are unlocked.
Internal Organs and the Immune System
Immune system cells are stored in different organs in the body.
The thymus, a soft organ in the upper torso or neck, processes and stores T-lymphocytes, allowing the cells to finish maturing. The organ is at its largest in childhood and shrinks in adulthood. It also produces thymosin, a hormone that increases lymphocyte production. As a person grows older, the other organs pick up the slack and become more important to the immune response.
The spleen is a soft organ shaped like a glove and located near the stomach. It filters the bloodstream and acts as a source of spare red blood cells in case of injury. It also holds several lymphocytes, including T and B cells. The spleen is a common place for immune system cells to come into contact with pathogens in the bloodstream. It also finds and destroys defective red blood cells, refreshing the blood. It may have other immune regulation functions, too.
Lymph nodes are areas where immune system cells are stored and where lymphatic fluid flows through and is filtered. There is a whole system of lymph vessels that connect between the nodes and, separate from the bloodstream, transport the cells to where they need to go. The lymph nodes are located in the joints and in the neck, and swell up during injury and, especially, sickness. They can prevent pathogens and poison from traveling beyond the limbs.
Because of the complexity of the immune system and health in general, nearly every organ in the body plays some role in the immune response. (Interestingly, the brain and eye are protected from most immune responses.)
The Immune System & Lupus
The most common type of lupus is Systemic Lupus Erythematosus (SLE) and it is an autoimmune disease. Lupus occurs when the immune system attacks the body’s own cells instead of attacking just pathogens and virus-infected cells. Then, the system error that causes this can result in antibodies that target the body’s own cells. This ingrains the error into the immune system’s memory and ramping up the response and the damage it causes. These “auto-antibodies” can be detected by blood tests called ANA tests.
It’s still not clear what part of the immune system goes awry with lupus. T-cells and B-cells are potential culprits, and also potential targets for medications.
The immune system malfunctions associated with lupus may also be a general series of health issues caused by stress. Stress and anxiety are linked to physical and chemical changes in the brain and body that can affect the immune system and general health. It is a well-known phenomenon for stressful occupations and life events to be linked to flares. Or even the first diagnosable onset of lupus. Avoiding or reducing stressful situations can be difficult in this day and age. But treating anxiety and modulating stress can help with symptoms.
In either case, most medications for lupus involve the immune system and its components. Different medications affect different parts of the immune system or what stage of the inflammatory process that they target. This affects their side effects and effectiveness. You can read more about specific medications for lupus, here.
A Lupus Warrior’s Takeaway
Your immune system is important for both your symptoms and your overall health. It needs to strike a balance. Not so aggressive that it damages your body, but not so weakened that it lets in pathogens and makes you even more sick. Sometimes, though, lupus won’t let you make that choice, and you will need to take medications like immunosuppressants that suppress your immune system.
But, your lifestyle can have a major impact on how you feel. Stay as healthy as possible through a healthy diet, regular exercise, plenty of sleep, and avoidance of what stresses you can. Probiotics are potentially useful for improving immune system health and lupus, and you can read more about what we know about probiotics and lupus here.
Proper hygiene can help, too – preventing the pathogens from entering your body in the first place. This can help calm the immune system, too. You can read more about hygiene and lupus, here.
In short, your immune system is a part of you. Take care of yourself, and your immune system will be taken care of along with it.
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8 thoughts on “An Overview of the Human Immune System”
Very interesting I had Lupus for over 37 years i went true many flare up,
You don’t have lupus now?
Thank you for writing about Lupus in a way people around us can understand. I have been flaring one right after the other for a year now. This comes after flaring constantly but manageable for 4 yeats. I’ prefer to isolate from everyone so I don’t have to say I’m having a flareup. I’m tired of my immune issues. It’s easier to just go to bed and try to calm the racing thoughts of identifying what just did this, how can I move away from triggers, feeling the pain in my stomach Identifying if it’s my pancreas and if so why am I experiencing a few new symptoms with pancreatitis, and separating hunger pangs from inflammation pain. God it’s too much. I judge myself when I need recovery from being clinically burnt out as a tax and business services owner considered on the financial front line, hey just the pandemic itself is tearing up the health of so many! I’m angry trying to sort out problems never risen before for my clients, really the entire country/world. Medical/financial/emotional health complexities have bankrupted our USA to a mere mess of a third world country. I have experienced the daily living of both. Thank you for giving me space to write out, this is how I feel and the reason why I cannot because my time is spent on managing everything
you just read~myLupus and its sucky right now.
Sorry to hear that you are having a rough time. You are right… It sucks!!!
I find online meditation group sessions very useful. Would that be something that you might consider? Hope you feel better soon xxxx
My blood test showed I have lupus
What type of probiotics is the best.
nucific bio-x , sold online, wait for a sale, i was using a cheap probiotics and switched to this, seemed to make a difference.less gas and better bowel movements,
Lupus does suck and 2020 has not helped at all! It’s been one flare after another!