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October 20, 2022 - January 9, 2023
The inflammation retracts and blood vessels constrict again, while the excess fluid leaves the now-former battlefield, transported away through the lymphatic vessels. The bloated tissue constricts slowly to its former dimensions. The damaged tissue is already regrowing, young civilian cells take the place of the fallen. Regeneration is on its way.
Right now your Adaptive Immune System has a specific weapon against every possible enemy in the universe.
A bacterium consists of one cell. And it can produce another fully grown-up bacterium in about half an hour.
but by pure random chance from time to time, there will be an individual that adapts to your defenses and becomes a pathogen: A microorganism that causes disease,
Worse still, even in the midst of an ongoing infection, the genetic code of invaders can change in ways that make them harder to kill.
What you will now learn may be the most amazing aspect of your immune system. It will take us a few chapters and will introduce not only mind-blowing principles that keep you alive, but also your best defense cells and things like Antibodies, something we hear about quite regularly in the media, especially in the wake of the novel coronavirus.
To recognize a bacteria and to grab it, your immune cells need to connect to the protein puzzle pieces of bacteria.
the language of immunology, a protein piece that is recognized by the immune system is called an antigen
An antigen is a piece of an enemy that your immune system can recognize.
In your body right now, there is at least one immune cell that has a receptor that can recognize one of the many millions of different antigens that can exist in the universe.
But wait a second. Receptors are made from proteins and as we discussed earlier, a gene is the code to build one protein.
Wait. How can you get such an enormous variety of receptors if our genetic code is so much smaller?
evolution has given your immune system a small number of gene fragments, not even whole genes, but fragments.
this is what your adaptive immune cells do with gene fragments. It takes gene segments and randomly combines them, then it does the same again, and then it randomly pulls out or adds in parts, to create billions of different receptors. They have three different groups of gene fragments.
But there is a catch—this ingenious way to create such stunning variety makes your adaptive immune cells critically dangerous to you. Because what is stopping them from developing receptors that are able to recognize self, the parts of your own body? Well, their education is. So let us finally talk about your most important organ you have never heard of.
Your Thymus is absolutely crucial for your survival and, in a way, will decide at what age you will die,
Some of your most powerful, crucial adaptive immune cells are educated and trained here: T Cells.
T Cells do a variety of things, from orchestrating other immune cells, to being antivirus superweapons, to killing cancer cells.
before they can fight for you, they need to pass the horribly dangerous curriculum in the Thymus.
each individual T Cell is born with ONE specific type of receptor, able to recognize ONE specific antigen. But there is a vital flaw: With so many different receptors there are guaranteed to be a large number of T Cells with receptors that are able to connect to proteins from your own cells. This is not a theoretical danger, but the cause of a number of very real and serious diseases that millions of people are suffering from right now called autoimmune diseases.
At least 7% of all Americans suffer from autoimmune diseases
an autoimmune disease is your adaptive immune system thinking that your own cells are enemies,
The T Cells that pass test one have functional receptors. Great job so far! The second test is called positive selection: Here the teacher cells check if the T Cells are really good at recognizing the receptors of the cells they will need to work with.
The final exam is simply: Can the T Cell recognize self
The only acceptable answer is “No, not at all.”
the teacher cells in the Thymus that do the testing have a special license to make all sorts of special proteins that usually are made only in organs like the heart, pancreas, or the liver and also hormones, like insulin for example.
Roughly ten to twenty million T cells will leave your Thymus today.
Your Thymus basically begins shrinking and withering away when you are a small child.
until around the ripe age of eighty-five, your T Cell university closes its gates for good.
The absence of the immune cell university is one of the most important reasons why seniors are much weaker and more susceptible to infectious diseases and cancer than younger people.
When an infection occurs, your immune system determines which specific defense is needed and how much of it. The adaptive immune system works together with the Innate Immune System to find the few cells that have the right receptors for this specific invasion, locate them among billions of others in your huge body, and then rapidly produce more of these cells.
How does it do this? By preparing a presentation
is the Innate Immune System’s job, and this is where the Dendritic Cell, this big, weird-looking cell with many octopus-like arms that takes samples, comes into play. When an infection happens it covers itself with a selection of the enemy’s antigens and tries to find a Helper T Cell that is able to recognize one of the antigens with its specific receptors.
Dendritic Cells literally disassemble pathogens into antigen-sized pieces and pack them into special contraptions on their membranes.
the Dendritic Cell then travels through the lymphatic system to present them to the Adaptive Immune System, or more precisely, to Helper T Cells.
All antigen-presenting cells have one thing in common: A very special molecule that is as important as the Toll-Like Receptors
Major Histocompatibility Complex class II. Or in short, MHC class II,
the cells of the Adaptive Immune System are extremely powerful. Activating them by accident has to be avoided at all costs—so a few special requirements have to be met before they are activated. And one of them is the MHC class II receptor,
Helper T Cells are able to recognize an antigen only if it is presented in an MHC class II molecule.
information about an infection is transmitted from your Innate Immune System to your Adaptive Immune System.
the Dendritic Cell a living information carrier.
After arriving in a Lymph Node, the Dendritic Cell has about a week to find a T Cell to activate before an internal timer runs out and it kills itself,
As the infection dies down no more new Dendritic Cell snapshots are sent to the Adaptive Immune System, the older sets of information die, and no new T Cells are activated.
The genes that are responsible for the MHC molecules are the most diverse genes in the human gene pool, leading to a huge variety of MHC molecules between individuals.
different types of MHC are better or worse at presenting antigens from different enemies,
this is enormously beneficial because it makes it really hard for a single pathogen to wipe us out.
This is so incredibly crucial for our collective survival that evolution may have made it a contributing factor in mate selection. In human words: You find potential partners with MHC molecules that are different from yours more attractive! OK wait, what? How would you even know this? Well, you can literally smell the difference! The shape of your MHC molecules does influence a number of special molecules that are secreted by your body—which we pick up subconsciously, from the body odor of other people—so you communicate what type of immune system you have through your individual smell!
We just find that if a potential mate has a different immune system, he or she smells sexier.
there are multiple classes of T Cells: Helper T Cells, Killer T Cells, and Regulatory T Cells, each able to specialize even more into various subclasses, for every possible kind of infection.
T Cells are the coordinators of the immune system.
