Our immune systems are pretty badass. Within each of us lie valiant microscopic warriors that can literally eat invaders, blast them with toxic chemicals or puncture their membranes with little protein spears, among other functions. All of this happens within a rather delicately balanced system of electrical signals and chemical messages in reaction to events happening around us and within us.
I started peeking into the immunological world as I was researching the stress response for a previous blog post, The Axis: How Stress Works. The relationship between stress levels and immunity caught my attention, especially considering the current sweeping, global, viral pandemic. The acute stress response temporarily shuts off several processes of the immune system, and chronic stress can wreak havoc on the system as a whole.
How interesting is it that the process that exists to prepare us to deal with imminent danger, through things like increased heart rate, more blood to skeletal muscles and heightened awareness, also suspends our ability to deal with internal threats?? (like viruses, bacteria, parasitic worms, toxic chemicals, etc... ie) pathogens)
In this post we will take a deeper look at how the stress response, specifically cortisol, does the work of shutting off our internal defenses when it kicks into gear. But first, let’s get a basic understanding of of the the immune system, consisting of a large network of cells varying widely in type, function and structure. These cells, generally known as white blood cells, are broken down into two main categories, according to their mechanism of action.
Below are just a few animated examples of what our immune cells get up to in there. Obviously, there are way more processes that occur to make the system work, and it's way more complex than a sharpie drawing. But this can at least give you some appreciation for the microscopic mini-dramas occurring within you.
This cell, the neutrophil, part of the innate immune system, connects proteins within its plasma-floating globules into a giant spear that punctures the membrane of an invader. It then proceeds to consume the entrails. Yum! Neutrophils are named as such because under a microscope, they react neither to an acidic nor basic stain. Therefore, they are neutral (neutro-) loving (-phyllic).
Dendritic cells hang out where your body is in contact with the external environment (nose, lungs, skin) and wait for a pathogen that it’s interested in. When it finds a worthy opponent, it tickles the pathogen with its tentacles and nibbles on it (in a process literally called “nibbling”) to get some of its chemical structure. Once it has enough presentable evidence, called an antigen, it will migrate to the lymphoid tissue and present its nibblings to the adaptive immune cells so they can start constructing an antibody.
The basophil, part of the innate immune system, signals other cells through the release of histamine in the case an inflammatory or allergic reatction, which not only recruits other cells to the scene but also makes capillaries more permeable so cells can easier move from blood to tissue. Like the neutrophil, the basophil was named for its reaction to pH stains. It reacts most to a basic stain, therefore it is basic (baso-) loving (phyllic).
Left: Helper T Cell activates and recruits other immune cells. There is an incredible amount of communication that occurs between cells of the immune system. A whole network of warriors that aren’t afraid to ask for what they need. Adaptive immune cells will usually hang out in tissue, maturing and doing other cell-y things, until the scavenging, more mobile cells signal a need.
Right: Cells will often kill themselves after doing their job in a process called “apoptosis”. While it may seem drastic, this is necessary to keep the immune system from attacking itself. The cells that squirt out crazy chemicals to kill intruders would end up intoxicating the whole body and eating away away all your tissue if it kept up its work after an intruder was dead. So after it’s done the noble work of protecting your physical vessel, that cell will valiantly step down for the good of the system and bid farewell to its membranous abode.
Here, again, we see the neutrophil. Often first on the scene of tissue damage or inflammatory response, this one is smothering an invader with chemicals that destroy the membrane and melt that bugger away. Will it proceed to consume the leftovers? Probably.
***BONUS NERVOUS SYSTEM EDUCATION!!!***
(Yes, the brain and spinal cord have their own special, though not separate, immune system
Microglia (greek for "little glue") were initially thought to serve the sole purpose of holding neurons in place but actually act as immune cells of the nervous system. They live in the meninges, or the protective layering around your brain and spinal cord. Microclia lodge in one place (they're glue, after all) and have tentacles that feel around for intruders, kind of like the dendritic cell. If the tentacles feel the unpleasant itch of a pathogen, its cell body will expand enough to completely engulf the pathogen. After it consumes the invader, it will shrink back to its original size, spit part of the pathogen back out, present it on one of its tentacles and send some chemical signals that recruit adaptive immune cells to come take a look at what it caught so they can create antibodies. Once the antibodies are created, those cells can then better deal with that pathogen later if it circulates through the system because it will be recognized and demolished.
Now that we have some background, let’s swing back around to how exactly the stress response, cortisol specifically, shuts down immune function. This is a complex system with a myriad of possibilities, differing person to person and moment to moment. However, we’ve been able to study some of these reactions and get a general idea of what happens when the immune system slows its responses in the presence of cortisol. Here are a few ways that it works.
1) Suppresses the production of chemical messages from cells so they cannot stimulate other cells to come join the fight in some cells
2) Restricts the capacity of dendritic cells’ maturation, survival, movement and function. When these cells can no longer travel and work as usual, they cannot move through the blood detect invaders or to lymphoid tissue to present its antigen to T Cells. Cortisol can also make dendridic cells tolerogenic, which means tolerant of immune suppression, so they can no longer detect invaders. This also affects the capacity of the dendritic cells to signal T Regulator cells, which play a role in regulating how many immune cells are active in an area at the same time. So by hampering the structure and function of dendritic cells, both branches of the immune system, innate and adaptive, are suppressed.
3) Reduces circulation of T Cells by enhancing their migration back to bone marrow and other lymphoid tissue
4) Draws neutrophils out of bone marrow and into the blood stream, simultaneously hindering their ability to migrate to inflamed sites. This means that there are a lot of hungry phagocytes out there not knowing where to go, triggering a body wide inflammatory response of backed-up of immune cells. It has also been shown to promote neutrophil apoptosis, or cell suicide.
5) Crosses the blood brain barrier to act on microglia, immune cells in the nervous system, and suppress the production of chemical messages that tell other immune cells to come help
All these little functions that are impaired by cortisol are necessary when an individual is facing danger. Shutting down certain functions allows the energy of the body to be directed elsewhere. Acutely, this is something the body can handle and bounce back from. In fact, after an imposition of eustress the body actually learns to recover from the stress response faster and quicker. Chronically, constant exposure to cortisol can potentially wreak havoc on the immune cells, both dampening their response and confusing their overall function.
So on a deep level, learning to understand your own personal emotional and physical responses to stress creates a stronger, healthier you. Sometimes it’s easy to access our brains "rest and digest" parasympathetic state, to chill out and relax (cooking, quiet walks, giving or getting a massage). Other times it can be really difficult to sit still, to take time, to really acknowledge and own your shit. Honestly, it requires some discipline to regularly take yourself out of a reactionary, stress induced state and purposefully focus your efforts on reducing stimuli, slowing the breath, and being more still. But it’s worth it. It’s in this parasympathetic state that our body is able to truly do its supportive work, to run all those little functions that keep us, quite literally, together. In this state that our immune system re-calibrates and enlivens.
Stress management includes and goes beyond emotional regulation. It’s important to understand that tending to the self, emotional, mental and physical, goes beyond bath bombs and sugar scrubs, and it does more than just make you feel good. It strengthens your immunity! Sincerely understanding your reactions to life and working with your own ability to handle stressors affects you deeply and biologically. Taking care of you matters.
I challenge you to take inventory of your restorative practices. Be it meditation, a movement practice, a quiet walk outside, sipping tea in the dark, preparing a nutritious meal, just being quite for a while and looking around…whatever works for you. Do them regularly, with relative discipline, with love and knowing that by giving the body and brain time to recover, you’re allowing all the parts of yourself that make you strong and resilient, even more so. Visit this website’s resources page for access to guided meditations and movement videos if you need somewhere to start.
Thanks for reading,
“The HPA-Immune Axis and the Immunomodulatory Actions of Glucocorticoids in the Brain” Bellavance, M.A., Rivest, S. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978367/
“A Biopsychosocial Model Based on Negative Feedback and Control. Carey, T.A., Mansell, W., Tai, S.J. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3937810/
“Inhibition of Microglial Cell Activation by Cortisol”. Drew, P.D., Chavis, J.A.. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3937810/
“Cytokines, Inflammation and Pain”. Zhang, J.M., Jianxiong, A. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785020/
“The Innate and Adaptive Immune Systems”https://www.ncbi.nlm.nih.gov/books/NBK279396/
“Principles of Human Anatomy” Tortora, G.J., Nielsen, M.T.
“A role for class A scavenger receptor in dendritic cell nibbling from live cells.” Harshyne, L.A., Zimmer, M.I., Watkins, S.C., Barrat-Boyses,