Your immune system: Natural born killer발음듣기
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Your immune system: Natural born killer
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And while the sex part is, I'll grant you, a little bit sexier, not dying is also really fantastic, something that I personally like to do every single day.발음듣기
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I personally like to not die in all sorts of ways, like I don't jump out of planes, I don't go into active combat zones, I don't do heroin.발음듣기
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I can, however, spend time wallowing in the filth with my cute bacon-producing friends here and not have to worry about dying because somehow my body can handle a lot of little devils on my hands, in my air, in my food, little things that literally want to kill me.발음듣기
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There are more potentially human killers in this pig pen than there are in all of the world's prisons but I don't have to worry about it because of an elite team of microscopic assassins that live inside my body, my immune system.발음듣기
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(upbeat music) You've heard of some of these little ninjas, others maybe not, but everyone knows the work they do by the trail of dead that they leave behind, pus being the most disgusting example.발음듣기
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They not only identify incoming enemies, they eliminate them and then they keep files on them in case their kind ever comes back.발음듣기
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So I don't want to freak you out but you and I are covered in pathogens right now and you really can't blame them for wanting to get a piece of your action, you warm, high energy, nutrient rich, salty watery action.발음듣기
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Your body is pretty much a theme park for these guys and although the majority of organisms living inside you actually make your life more comfy, there are some less helpful viruses and organisms from here on out referred to as pathogens that will want to turn your body into a factory for their children. So let's avoid that.발음듣기
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Innate, or non-specific immunity, that responds to all kinds of pathogens the same way and very quickly whether your body has seen that pathogen before or not.발음듣기
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And your acquired, or adaptive, immunity which develops more slowly and requires your body to learn the wily ways of the pathogen before it defeats it.발음듣기
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Every animal has an innate immune system, even sponges, but only vertebrates have the acquired kind.발음듣기
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You were born with your innate immune system and from the second that you wiggled your way out of the sterile environment of your mom and into this germ-y disgusting world, that system has been protecting you.발음듣기
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The thing about the innate immune system is that it doesn't care what it's killing, it doesn't worry about whether it's offing a virus or a bacteria or a fungus, its job is to just keep the enemy from getting in.발음듣기
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The first line of defense in keeping sketchy characters out are the skin and mucous membranes.발음듣기
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The skin has so many excellent functions, like keeping your organs in, that it's easy to forget that its primary purpose is to keep things out.발음듣기
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It's oily and kind of acidic and really not easy to penetrate and I'm about to rock your world with this, but your digestive tract is also technically the outside of you.발음듣기
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Well the inside of that tube is exposed to as much weird, grody stuff as the outside of the tube.발음듣기
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So your body treats the digestive tract like the front lines of this war which is one of the reasons why your stomach takes no prisoners with the whole stomach acid situation.발음듣기
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In addition to things like skin we've also got mucous membranes providing another barrier to microbes trying to sneak in.발음듣기
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Mucous membranes line all of your internal surfaces that are exposed to the outside like your lungs and the inside of your nose, as well as some other parts of your body like the inside of your mouth and your eyelids and your sex organs.발음듣기
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Mucous membranes unsurprisingly produce mucous which is a viscous fluid, you've probably heard of it, and it traps microbes and helps sweep them away.발음듣기
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The honchos here are specialized cells in your connective tissue called mast cells that constantly search for suspicious objects, usually unknown proteins, and then release signaling molecules like histamine when they find them Histamine makes your blood vessels more permeable which allows a whole bunch of fluid to flow to the affected area and that is what causes inflammation.발음듣기
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But it also brings in a crapton of white blood cells, infection fighters, to go all Balrog on whatever's trying to make its way in.발음듣기
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This is great if you get a splinter in your toe or a bunch of viruses in your face, but sometimes something gets into you that's not actually dangerous, like pollen or dust or like, a peanut and your immune system triggers an inflammatory response anyway even though it's not a big deal.발음듣기
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This is what we call an allergic reaction and you know what those are like with the swelling and the redness and the mucous production and the itching and the occasionally a little bit of death, so that is why we take antihistamines to suppress the histamine triggers so our immune system stops freaking out about nothing.발음듣기
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Most of the immune system activity that happens inside your body's fortress is done by white blood cells or leukocytes.발음듣기
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Leukocytes are awesome for a lot of reasons but one reason is they've got full VIP access to anywhere in the body that they want to go with the exception of the central nervous system, the brain and the spinal cord which are for obvious reasons, super high security areas.발음듣기
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Leukocytes can move through the circulatory system and when they get to a place where they're needed they can basically send a signal to ask the capillary to open a gap between its cells and then it oozes through that gap to the site of the infection.발음듣기
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Now there are a lot of different kinds of leukocytes, like different branches of your own personal microscopic army.발음듣기
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More Greek this time, phago meaning eating and they're just any cells that ingest microorganisms through the process of phagocytosis.발음듣기
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Phagocytes are pretty cool, they can literally chase down invading cells, grab them and then complete engulf them.발음듣기
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And some, like the superabundant neutrophils, move around the bloodstream and can quickly get to where the action is.발음듣기
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The big eaters which don't generally travel a lot but instead hang out like bodyguards in your various organs.발음듣기
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Not only do they kill outside invaders, they can also detect when one of your cells has gone rogue, like a cancer cell and kill those too.발음듣기
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Of all the grizzly stuff that goes on in the never-ending street war that is your immune system, some of the most gruesome stuff is done by a kind of cell called natural killer cells.발음듣기
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Wade, Watergate. It was a tumultuous time but part of me wishes that you, 1973, had an opportunity to name everything in biology because you got one chance to name a new type of immune cell and you named it the "Natural Killer Cell" and I freaking love that.발음듣기
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I look around at today's script with all of its dendritic cells and macrophages and diapedesis's and I think, what if we let 1973 name all these things?발음듣기
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I don't know, maybe you would have screwed it up but I don't think we could have done any worse than all this G.D. Greek we have to deal with all the time.발음듣기
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Okay, natural killer cells, more than just a great name, also the only phagocyte in the innate immune system that destroys other human cells.발음듣기
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When your cells are healthy they have a special protein on their surface called MHC1, MHC for major histocompatability complex.발음듣기
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But when your cells are infected, say with a virus or when they're cancerous, they stop producing that protein.발음듣기
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So the natural killers are always going around, checking up on each of your cells and when it finds one that's not normal, it pulls out its AK-47 and unloads.발음듣기
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Actually it just binds with it and then secretes an enzyme that dissolves its membrane, but still, killing.발음듣기
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Finally dendritic cells are a type of phagocyte that hangs out on the surface of much of your body that comes in contact with the environment.발음듣기
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They eat up pathogens and then carry information about them back to the spleen or the lymph nodes where it passes intelligence about what's going on in the war front to the acquired immune system.발음듣기
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I actually studied dendritic cells in my undergraduate thesis and I kind of fell in love with them.발음듣기
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The activity of these cells gives us a chance to transfer from the innate immune system to the acquired immune system which is going to make things a little more complicated.발음듣기
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The acquired system has to learn as much as it can about every pathogen it interacts with, store that information, and then use it to invent defensive's against them.발음듣기
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Harvesting bacteria and other stuff, not just good bacteria that can help your guts out but also harmful ones that your body learns from and stores information about.발음듣기
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That system keeps an eye out for any foreign substance, a toxin, a virus, a bacteria, even parts of those things that could be telltale signs of a bad guy.발음듣기
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An antigen is anything that causes your immune system to I.D. a pathogen and then create an antibody against it.발음듣기
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Now antibodies aren't cells, they're highly specialized proteins produced by B cells to recognize and help lay the smack down on intruders.발음듣기
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The best that they can do by themselves is sort of swarm all over the invader making it harder for it to move and to excrete toxins or otherwise infiltrate healthy cells, but more often antibodies serve as tags, attaching themselves to the scumbags and then releasing chemical signals to nearby phagocytes alerting them that it's dinner time.발음듣기
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Your acquired immune system also has its own type of white blood cells, not phagocytes which go after everything that is a little bit sketchy, but lymphocytes which go after specific things that they already know about.발음듣기
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The T cells which form in your bone marrow and then migrate and mature in the thymus gland right behind your breastbone.발음듣기
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What T and B actually stand for is a long story but if it helps you to remember, T's mature in the thymus, B's in the bone marrow.발음듣기
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We have two different types of lymphocytes because our bodies have two different types of acquired immunity.발음듣기
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The cell-mediated response which is for when the cells are already infected, and the humoral response for when the infection is just in the humors, the body's fluid, not in the cells.발음듣기
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This process mainly involves T cells and there are quite a number of different types of them.발음듣기
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Helper T cells have a cute sounding name but in a lot of ways they call the shots for the whole immune system.발음듣기
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If 1973 had named them they might have been called admirable T cells or something more awesome.발음듣기
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After the deed has been done it has the ability to shred up the proteins from an invader and put a bit of that antigen on its membrane surface.발음듣기
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A helper T cell can detect when this happens and it comes over to attach itself to the presented antigen.발음듣기
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The antigen presenting cell produces a chemical called interleukin 1 which basically tells the helper T cell, uh boss, I found this guy over here and then I broke his neck and then he stuck his guts all over my cell wall.발음듣기
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The helper T cell gives it a look and then releases a chemical called interleukin 2 which is like a bullhorn, an alarm that tells all of the lymphocytes in the area there are problems here, we've got a problem over here in sector 15.발음듣기
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Most of those copies differentiate into effector T cells, which travel around secreting signaling proteins that stimulate other nearby lymphocytes to take action.발음듣기
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Most of the rest of them become memory T cells, they're the ones that keep a record of the intruder and provide us with future immunity against it.발음듣기
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And now for the saddest story of the day, what happens when a cell gets infected, so infected that it knows it's a goner, that it in fact is being converting from a healthy useful part of the body to an evil zombie farm pumping out viruses or bacteria, suddenly co-opted to help destroy everything it loves.발음듣기
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Once a cytotoxic T cell gets the message from the helper T cells that there's an infection to deal with, it starts patrolling the area for any normal cells presenting antigens.발음듣기
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When it finds one, it latches on to it and releases enzymes that create holes in the cell's membrane and eventually breaks down the whole cell, killing the cell and the pathogen in the process.발음듣기
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The humoral response is designed to catch pathogens that are floating around in your body that haven't actually invaded any of your cells yet.발음듣기
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The primary players are B cells which are constantly patrolling your blood stream like cops walking the beat until they get a signal from a helper T cell that something's wrong.발음듣기
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A single B cell can be covered in a forest of up to a hundred thousand antibodies, say for the virus that causes the common cold.발음듣기
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And the B cell next to it will have just as many receptors for a different antigen, for chicken pox or something.발음듣기
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When a B cell bumps into a pathogen that it recognizes, it attaches to it and starts cloning itself like crazy.발음듣기
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Suddenly there are tons of that B cell with the same receptor, but during the cloning process the clones differentiate into new versions of the original just like the T cells did.발음듣기
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Most turn into plasma or effector cells which use the antibody as a blueprint to create a crapton of antibodies for that specific pathogen. Like 200 antibodies per second.발음듣기
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Once these antibodies are released, they bind to the pathogens like crazy, marking them for death until the phagocyte can come along and do the dirty work.발음듣기
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The rest of the cloned B cells mostly become memory cells which have the same receptor and stick around providing future immunity from this invader.발음듣기
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And we are now very out of time but I really love this stuff so I didn't want to gloss over anything.발음듣기
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Mucous, natural killer cells, macrophages, killing things, breaking them up and sticking them on their cell membranes.발음듣기
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Effector cells spewing out antibodies and memory cells making sure that our immune systems hold that grudge.발음듣기
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