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Pus is the dead bodies of millions of Neutrophils that fought to the death for you, mixed in with ripped-apart remains of civilian cells, dead enemies, and spent antimicrobial substances.
Without your Neutrophils’ sacrifice, this infection would have spread already. Maybe to the bloodstream, which would give the intruders access to the whole body and that would be really, really bad.
The Dendritic Cell is on its way.
They identify what kind of enemy is infecting you, if it is a bacterium or a virus or a parasite. And they make the decision to activate the next stage of your defense: Your adaptive immune cells, your heavy, specialized weapons that need to come in if your innate immune system is in danger of being overwhelmed.
Not only is the Dendritic Cell able to distinguish if an enemy is, for example, a bacterium, it can distinguish between different species of bacteria and knows what sort of defense is needed against them.
the Dendritic Cell has to enter the Immune System Superhighway: The Lymphatic System,
A very fascinating example is the bacterium Klebsiella pneumoniae, a pathogen that causes, among other horrible things, pneumonia. It avoids the whole complement affair by hiding itself from complement proteins behind a sticky and gooey structure called a capsule. Which is quite literally a slimy sugary coat the bacteria produce to cover the molecules the immune system would recognize. Simple and effective, like a deodorant for bacteria.
Your lymphatic system begins as a tight and complex network of capillaries spread throughout your tissue.
They are built like a series of one-way valves—water can enter them from the tissue but it cannot flow back.
The Spleen is a sort of large lymph node,
For one, the spleen is the place in your body where 90% of your old blood cells are filtered and recycled when their life comes to an end.
25 to 30% of your red blood cells and 25% of your platelets (remember, the cell fragments that can close wounds) are stored here for emergencies.
The main home for another immune cell we did not mention before even though it did help out during the cut: the Monocyte.
If you suffer an injury and an infection that drains and kills a lot of your Macrophages, they come in as backup.
they are called to the heart during a heart attack to help the heart tissue with healing itself.
the spleen really is just a huge lymph node that filters your blood (and not your lymph fluid, like your regular lymph nodes do)
Other organs like the liver, regular lymph nodes, and your bone marrow can take over most of its jobs.
The Tonsils are known to people only as weird lumpy things in the back ends of their throats that sometimes have to be surgically removed in children.
Your tonsils are something like a center of your immune system intelligentsia in your mouth.
your tonsils have deep valleys where tiny pieces of food can get stuck. Microfold Cells, very curious cells that grab all sorts of stuff from your mouth and pull it deep into the tissue, where they show it to the rest of the immune cell to check
If your tonsils are overeager and work too hard, they can become chronically inflamed and swell up, which can cause all sorts of unpleasant symptoms.
what you really need to know about your tonsils is that they are immune bases that actively sample what comes into your body.
the Lymphatic System is your fat transportation system. It picks up food fats around your intestines and dumps them into the bloodstream to be further distributed.
Exhausted by a seemingly endless war, a spent Macrophage slowly moves over the battlefield looking for bacteria to kill.
then it notices something. Thousands of new cells arrive at the battlefield and spread out quickly.
These are Helper T Cells! Specialist cells from the Adaptive Immune System were forged just for this particular battle and they exist only to fight this specific soil bacterium
it moves directly towards the tired Macrophage and whispers something, using special cytokines to convey its message.
All over the battlefield this begins to happen as Helper T Cells whisper magic words to tired soldiers, motivating them to get themselves together and engage the bacteria again,
Another tiny army—this time directly made by the Adaptive Immune System—has joined the fight. Counting in the millions, it floods the battlefield, dashing against the enemies. The specialist forces of the Antibodies have arrived! Although they are made from proteins just like complement, antibodies are very different.
At some point the last panicked bacterium is devoured whole by the once-tired Macrophage.
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.
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.
through controlled recombination, your immune system is prepared for every possible antigen an enemy could make.
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?
The Thymus is an unappealing and boring collection of tissue
it is one of your most important immune cell universities
your most powerful, crucial adaptive immune cells are educated and trained here: T Cells.
Without T Cells you are quite dead—they may be the most important Adaptive Immune Cell you have.
let’s say a T Cell receptor can connect to a protein on the surface of a skin cell, it would not understand that it is connecting to a friend. It would just try to kill it.
an autoimmune disease is your adaptive immune system thinking that your own cells are enemies,
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. This way they can show the T Cell all kinds of proteins
Your Thymus basically begins shrinking and withering away when you are a small child.
Actually T Cells got their name from the Thymus, because they go to school here!
The Dendritic Cell is an antigen-presenting cell,
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.
Helper T Cells are able to recognize an antigen only if it is presented in an MHC class II molecule.
To activate your Adaptive Immune System, a Dendritic Cell needs to kill enemies and rip them into pieces called antigens,
These antigens are put into special molecules, called MHC class II molecules,
