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Basically, in order to be properly activated, B Cells have to become antigen-presenting cells. This works because B Cell Receptors are very different from T Cell receptors, which need the hot dog bun to recognize a very tiny piece of antigen.
So when a B Cell receptor connects to a turkey drumstick, a big chunk of antigen, it swallows it and processes it inside itself, just like a Dendritic Cell would. It slices the big chunk of meat up into dozens or even hundreds of tiny sausage parts, all the size of wieners. And these tiny parts are then put into MHC molecules (hot dog buns) on the surface of the B Cell. Basically, a B Cell takes a complex antigen and turns it into many processed, simpler pieces that are then presented to the Helper T Cell.
Step 1: A battle needs to occur and dead enemies, which are big chunks of antigens (turkey drumsticks), need to float through the lymph node. Here, a B Cell, with a specific receptor needs to connect to the antigen. If the dead enemy is covered in complement, activation will be much easier. This will activate the B Cell, which makes a lot of copies of itself and produces low-grade antibodies, but the B Cells will die after around a day if nothing more happens. Step 2: In the meantime, a Dendritic Cell needs to pick up enemies at the battlefield and turn them into antigens (wieners) which are
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if a T Cell recognizes an antigen that a B Cell presents to them, it stimulates the B Cell. This stimulation is like a gentle kiss or a warm encouraging hug. Not only does this prolong the life of the B Cell, it also motivates it to try to improve the Antibody! Every time a B Cell receives a positive signal from a Helper T Cell, it begins a round of purposeful mutation. This process is called Somatic Hypermutation (also known as Affinity Maturation) and we will never use this clunky term again.
Another thing Antibodies can do with their cute butts is to activate the complement system. Complement, as efficient and deadly as it is, when it is only by itself, its abilities are limited and it relies on finding the surfaces of enemies with a lot of luck basically.
Again we see the principle of our two immune systems: The innate part does the actual fighting, but the adaptive part makes it more efficient with deadly precision.
We learned about the scope of your body, your cells, and some of your most common enemies, bacteria. About your soldier and guard cells that guard your insides, the mechanisms they use to identify and kill invaders, and how they use inflammation to prepare the battlefields of your body. We learned how your cells recognize things and how they communicate with each other. We explored the complement system that saturates every fluid in your body. We learned about your surveillance cells that get help when necessary. We learned about your internal infrastructure and how your body has billions of
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It covers all of your surfaces that interact with the outside that are wrapped inside you. Mucus is continuously produced by Goblet Cells,
This slimy mucus serves multiple purposes—in the simplest sense it is just a physical barrier so intruders have a harder time reaching the cells that it covers.
And mucus is not just a sticky barrier but also filled with unpleasant surprises similar to the desert kingdom: salts, weaponized enzymes that can dissolve the outsides of microbes, and special substances that sort of sponge up crucial nutrients that bacteria need to survive, so they starve to death inside the mucus.
the mucosa inside your stomach acts as a barrier that keeps the acid at a distance and protects the cells making up your stomach wall.
Epithelial Cells. These cells are the equivalent of your skin cells, if you want. They are the cells that directly sit on the border of your mucous membranes, only covered by the slime. They are your “inside skin” cells.
So first of all, the immune system of your intestines is a semi-closed system that tries not to mix too much with the immune system in the rest of the body.
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. These bacteria are called commensal bacteria,
In a nutshell there are three layers: First a layer of mucus filled with antibodies, defensins (we met these before on the skin, the tiny needles that can kill microorganisms), and other proteins that kill or damage bacteria. In the gut it has to be pretty thin and somewhat porous because all the nutrients from your food need to pass inside, and if the first protective layer were too good, you would starve to death.
Below the mucus layer, the intestinal epithelial cells are the actual barrier between the inside and the outside. Similarly to your lungs, the layer of epithelial cells protecting your insides is only ONE cell thick.
So below the epithelial wall is the third layer of the gut mucosa, the Lamina Propria, which is the home of most of the immune system of your gut. In the Lamina Propria, directly below the surface, special Macrophages, B Cells, and Dendritic Cells are waiting to greet the unwelcome guests:
As a consequence the Macrophages guarding your intestines have two properties: Firstly, they are really good at swallowing bacteria. And secondly, they do not release the cytokines that call in Neutrophils and cause inflammation. They are more like silent killers, casually eating bacteria that cross the line but without making a fuss about it.
And IgA does not activate the complement system and does not trigger inflammation, which are both very important here. IgA is really good at something else though: with its four pincers that reach in opposite directions, it is an expert at grabbing two different bacteria and clumping them together.
So a lot of IgA can create huge clumps of helpless bacteria that are transported out of the body as part of your poop. All in all, around 30% of your poop consists of bacteria—and a lot of them have been clumped up by IgA Antibodies (most disturbingly, around 50% of them are still alive when they leave you).
Pathogenic viruses are excellent at circumventing the immune system because they have a superpower: Nothing multiplies as fast as they do. And that also means that nothing mutates or changes as fast as viruses.
DNA, which carries the instruction manuals for all the proteins of the cell, but not just blueprints but also their production cycles. These proteins determine the development, function, growth, behavior, and reproduction of your cell. So whoever controls the protein production controls the cell itself. How does this work? Well, your DNA consists of smaller sections, your genes, and each gene is the instruction for one protein. To turn the instructions from a gene into an actual protein, this information needs to be transmitted to the protein production machinery in the cell.
How do genes transmit information? Well, they technically don’t do anything because genes are just sections of your DNA. To communicate the information stored in a gene to the rest of the cell, living things use RNA. RNA is a complex and fascinating molecule that fulfills a variety of different and crucial jobs. The one we care about in this context is to act as messengers that relay the building instructions from genes to the protein factories of your cells.
The influenza virus A, for example, just dumps a number of RNA molecules into the nucleus, where it pretends to be commissioned from your own genes and tricks the cell into building specific viral proteins.
Pyrogen loosely translated means “the creator of heat,” an extremely fitting name in this case. Simply put, 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. It also is a strong motivator to lie down and rest, to save energy, and to give your own body and immune system the time they need to heal or to fight the infection.*3
For one, it may generate more heat by inducing shivering, which is just your muscles contracting really quickly, which generates heat as a byproduct. 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. This is also the reason why you can feel so cold when you have a fever—your skin is actually colder because your body is trying to really heat up your core and create unpleasant temperatures at the battlefield to make pathogens really unhappy.
On average your metabolic rate increases by about 10% for every two degrees Fahrenheit your body temperature rises, which means that you burn more calories just to stay alive.
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.
There is the common wisdom that the color of your snot can tell what kind of infection you have and if it is just a cold or a flu, but that is not true: the color just tells you how severe the inflammatory reaction inside your nose is, not what caused it. The more colorful, the more Neutrophils have given their life.
Every cell of your body that has a nucleus (so not red blood cells) has MHC class I molecules.
