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Saliva contains a number of chemicals that help break down your food, so digestion really begins right after you begin eating.
Millions of years ago your ancestors made a fragile deal with a team of microbial species—humans provide them with a long, warm tunnel to live in and a constant stream of stuff they can eat, and in turn they break down carbohydrates that we can’t digest and produce certain vitamins that we can’t make ourselves. The bacteria of the microbiome are tenants of sorts and these resources are the rent they have to pay.
In the Lamina Propria, directly below the surface, special Macrophages, B Cells, and Dendritic Cells are waiting to greet the unwelcome guests:
inflammation means a lot of extra fluid in the intestines, which you experience as diarrhea. Diarrhea doesn’t just mean watery poop, but also damage to the very sensitive and thin layer of the cells that take up the nutrients from your food.
A virus is not much more than a hull filled with a few lines of genetic code and a few proteins.
The hulls of viruses are spiked with special proteins that can connect to a receptor type on their victims’ surface.
The Alveolar Macrophage. Its main job is patrolling the surface of your lungs and picking up trash.
In airways they downregulate other immune cells like Neutrophils and make them less aggressive. But most importantly, they tone down any sort of inflammation. Because the thing you really don’t want in your lungs is fluid.
There is evidence that your lungs might have a microbiome (which means a collective of microbes that live in your lungs),
the cell carefully wraps the virus inside a package and pulls it deep inside towards its nucleus, the brain of the cell.
the influenza tricks the cell into delivering its genetic material directly into the brain of the cell, the nucleus.
If you cut yourself and bacteria infect your wound, things are pretty straightforward: There is damage that immediately causes inflammation and attracts the immune system and there are a lot of enemies that don’t exactly act super discreet but more like a bunch of drunk toddlers in a candy shop.
The first real defense of your body against viruses is Chemical Warfare!
cytokines are the molecules that activate and guide your immune system.
There are a lot of different cytokines that are released in this situation and they do a lot of different things but here we want to highlight a very special class: Interferons.
Interferons are the ultimate “get ready for a virus” signal.
Every moment of your life your cells are recycling and reconstructing their internal building blocks and materials to make sure every protein is in good shape and works as intended. So some interferons tell cells to chill out a bit and to slow down the production of new proteins. If a cell doesn’t build a lot of proteins, it can’t build a lot of virus proteins if it happens to be infected already.
the next step on the escalation ladder of the antivirus section of your Innate Immune System: Plasmacytoid Dendritic Cells.
they are so sensitive to the signs of a virus infection, that only a few hours after the first of your civilian cells have been infected, they have opened the interferon floodgates.
soldier cells realize that they are dealing with a virus infection and that they need help on a larger scale, so they release another set of cytokines: Pyrogens.
pyrogens are chemicals that cause fever. Fever is a systemic, body wide response that creates an environment that is unpleasant for pathogens and enables your immune cells to fight harder.
they directly affect your brain and make it do things.
Your brain cranks up the heat in two main ways: For one, it may generate more heat by inducing shivering,
And by making it harder for this heat to escape by contracting the blood vessels close to the surface of your body, which reduces the heat that can escape through your skin.
Certain chemical reactions between proteins have a sort of optimal zone, a temperature range in which they are most efficient. By increasing the temperature in the body during fever, pathogens are forced to operate outside this optimal zone.
This is also the reason fever is helpful to your immune cells, since they can handle the heat, they can make use of the effect that higher temperatures tend to speed up certain reactions between proteins.
Your immune system needs to be able to kill your own cells. Your immune system has an actual license to kill you.
these cells go wrong, they could decide to kill healthy tissue and organs. And indeed, this does happen to millions of people each day and is called autoimmune disease,
The two MHC molecule types are crucially important and they have fundamental differences. MHC class I molecules are display windows. MHC class II molecules are hot dog buns! Very different things, annoyingly similar names!
Only antigen-presenting cells have MHC class II molecules.
This is it—no other cell is allowed to have an MHC class II molecule.*2 In contrast to that: Every cell of your body that has a nucleus (so not red blood cells) has MHC class I molecules.
The MHC class I molecule showcases these proteins to the outside world, just like a fancy display window would showcase a selection of the items the inside of a store has to offer.
One of the most important things that happens during the chemical warfare triggered by interferon is that cells are stimulated and ordered to make more MHC class I molecules.
Around 40% of the T Cells in your body are Killer T Cells and, just like their Helper T Cell siblings, Killer T Cells come with billions of possible different and unique receptors for all sorts of possible antigens.
These Dendritic Cells that are charged up with the snapshot of a battlefield from a virus infection are basically able to call for three different types of reinforcements: They activate the specific Killer T Cells that kill infected cells, and they activate Helper T Cells that help out at the battlefield and Helper T Cells that activate B Cells to provide antibodies.
the Killer T Cell punctures the infected cell and inserts a special death signal, that is conveying a very specific order: Apoptosis,
Natural Killer Cells hunt two types of enemies: cells infected by viruses and cancer cells.
They check if a cell has MHC class I molecules. Nothing more, nothing less. This is solely to protect against one of the best anti–immune system tactics virus and cancer cells have. Generally cells that are either infected or unhealthy do not show MHC class I receptors in order to hide what is going on inside them.
While the rest of the immune system looks for the presence of the unexpected, the presence of something other, Natural Killer Cells look for the absence of the expected, the absence of self. This principle is called “The Missing-Self Hypothesis.”
To prevent them from killing healthy cells, they have special receptors that calm them down, an inhibitor. A large stop sign receptor. The display window, the MHC class I molecule, is this stop sign, and it fits right into this receptor.
When Natural Killer Cells check out a civilian cell for infection or cancer, if they have plenty of MHC class I molecules, as most healthy cells do, the inhibitor receptor is stimulated and tells the Natural Killer Cell to chill. If the cell does not have enough MHC molecules though, there are no calming signals and the Natural Killer Cell, well, kills.
Killer T Cells flood into your lungs in the thousands, armed with receptors
If they detect virus antigens they order the infected cells to kill themselves. Macrophages work overtime to eat up all their dead friends and foes.
Millions and millions of Antibodies move in to eliminate the viruses outside of cells and stop them from infecting more cells.
Neutralizing Antibodies neutralize the virus by connecting firmly to the structures that the virus used to gain access into epithelial cells.
Other Antibodies can be very specific and block the virus in a variety of interesting ways.
Ribosomes are the structures that turn mRNA into proteins. So they are fundamental to the survival in both human and bacterial cells, because without new proteins, a cell must die.
Regulatory T Cells. They make up only about 5% of T Cells and in a sense are “opposite Helper T Cells.”
they can end an immune reaction or just prevent it from being triggered in the first place.
their most important job though is to act as a countermeasure to autoimmune diseases, where they prevent your cells from attacking your body.
