The human immune system is a topic that seemed foreign and not particularly pressing just several months ago. But the current coronavirus pandemic has brought the topic of immunity to the forefront of everyday conversation.
We’re going to demystify this topic so you can be better informed about what your immune system is and how it relates to another topic you hear much about: inflammation.
To begin, your immune system is not a system, but a set of systems that work together to protect the cells of your body. The two major branches of this system are innate immunity and adaptive immunity.
The Innate Immune System
Innate immunity is the collection of nonspecific protections that we are born with. These include the physical and chemical barriers of the skin and the mucous membranes inside of our respiratory and digestive tracts. These barriers trap and flush-out invaders, as well as facilitate immune surveillance.
The innate system also has several chemical defenses that are “non-specific” because they don’t target a certain species of pathogen, but they still protect against invaders. These include things like sweat, oil, tears, saliva, and wax that can help trap and kill pathogens.
Beyond the initial physical and chemical barriers, the innate system has a second line of defenses that include sensors, communicators, defenders, and biological responses such as inflammation and fever.
A major cell type involved in the innate response is known as granulocytes, which are leukocytes that consume and digest invaders. These cells patrol the blood and tissues looking for threats and can respond accordingly when they discover one.
Additional cells act similarly to find threats and then create cascades that mount an attack. However, these cells still are not responding to just one type of pathogen but are instead triggered by substances in bacterial cell walls or viral particles. This is why these cells are considered non-specific defenses.
When an immune cell finds a threat, it releases a chemical messenger known as a cytokine. Cytokines are small proteins used for communication that can alter the behavior of cells around them. This initiates the inflammatory response.
Inflammation is a coordinated reaction to a threat. This response can include swelling, redness, heat, and pain. The purpose of the response is to destroy an invader and remove its by-products as quickly as possible. However, when destruction is not an option, the cells try to wall-off the foreign material. The essential factor of inflammation is that it be able to extinguish, clear-out, and resolve the threat. When inflammation is sustained and cannot be resolved, it becomes dangerous to the host.
The Adaptive Immune System
The adaptive immune system is called as much because after it encounters, fights, and defeats a specific pathogen, it holds onto a “memory” of how to kill it again if it’s encountered. That’s why this branch handles specific immune defenses.
The adaptive immune system works in two ways. First, it has what’s called humoral immunity, which is composed of B cells and antibodies that patrol the blood. Second, it has cell-mediated immunity, which uses T cells to defend cells that are infiltrated by a threat.
“Humor” means fluids, which is referring to the adaptive response in body fluids that can eliminate threats outside of a cell. In this system, B cells become activated when they encounter an invader on their cell receptor. They then consume, process, and present the pathogen’s proteins on the outside of their cell membrane.
A secondary immune cell called a Helper T Cell then checks the protein to decide whether it is a threat or not. If it is, the B cell will transform into a plasma cell, which can then start producing antibodies.
Antibodies are small proteins that are produced to neutralize or destroy specific threats. Once the pathogen is defeated, some of those plasma cells will become memory cells, and then remember that one pathogen for life—circulating the body on patrol for it. This is one of the principles of vaccines.
The other branch of adaptive immunity is cell mediation. Rather than patrolling blood for an unbound threat, this response is all about dealing with a cell that is already infected.
In this scenario, the pathogen causes the proteins on the outer membrane of the compromised cell to change. Which signals a special immune cell, called an antigen-presenting cell, that looks for surface protein changes.
These cells sample the environment, collect foreign material, and then migrate into the lymph organs to present it to T cells. A T cell with the receptor for a particular foreign protein becomes “activated” once it encounters it. This transforms the basic T cell into a special type of Cytotoxic T cell that can then patrol the body for all fragments of this threat that it now “knows.” It can instruct any cell presenting that protein to kill itself using a process called apoptosis (programmed cell death).
Immunity in The News
Now that we’ve looked at the basic immune response from a 30,000-foot view, there are probably many key words standing out. Questions concerning antibodies, long-term immunity, and inflammation are at the forefront of national discussions. It’s important to note that all of these processes require a tremendous amount of nuance to understand fully.
Antibodies are an indication that a person has successfully dealt with a threat. When many people in a population have antibodies for a certain pathogen, “herd immunity” is developed.
The balance of immune responses is a delicate one. Some people’s immune systems over-respond to threats and incur what’s known as a cytokine storm. This can damage the host but is done so at the hands of one’s own immune system, not the threat itself. It’s not exactly known why this happens, but there is a lot of research looking into risk factors and contributing issues such as underlying diseases and dysregulated metabolic processes.
This is also why the concept of “boosting” the immune system is inaccurate. What would “boosting” entail? Having more immune cells? We know from cytokine storms and autoimmune diseases that immune systems that over-react do not benefit the host. Instead, we need to think of supporting the immune system—which is more about supporting a person as a whole.
What can you do to give your body the support it needs?
Habits and choices that promote total health over long periods of time are our best bet. However, what is simple is not easy. Americans are missing some of these factors entirely, but we can collectively make the decision to start prioritizing them. These include: not smoking, consuming a highly nutrient-dense diet, maintaining a healthy and lean body weight, drink alcohol sparingly, get at least 7-9 quality hours of sleep nightly, reducing chronic stress, and having diverse exposures to microbes in many different environments (fibers, forests, dirt, soils, water, and plants).
Above all, logic and healthy decisions are essential right now. We can focus on science to better understand what happens in our bodies and our population as we encounter microbes of all kinds. Then, we can make the choice to support ourselves and our community with healthy and resilient lifestyles. With that, we empower ourselves to make decisions regarding what we are in control of: our health.