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B 细胞、 CD4 + T 细胞和 CD8 + T 细胞综述

B细胞、CD4+T细胞和CD8+T细胞综述。 Sal Khan 创建




now that we've touched on all of the major players and the specific immune system what I thought I would do in this video is kind of do a summary so it all fits together a little bit so the first person or character we got exposed to is the b-cell which always do in blue the b-cell right like that and what made that interesting is that it every b-cell has its own specific or they have membrane bound antibodies but for each b-cell the membrane bound antibodies on each specific b-cell had its own variable portion so this b-cell that'll be variable right like that variable like that and if if I were to draw another V cell right here I would draw the variable portion a little bit different and this Y this is y different actual B cells will respond to different antigens or different pathogens that have entered our system and a b-cell gets activated it needs to get let me let me write all this down actually so if we're talking about a b-cell to get activated so let's talk about what happens when it gets activated or what needs to happen so activation it needs binding of the pathogen onto one of these membrane bound antibodies so binding of pathogen or maybe call it a mutagen or antigen and to gin but that's not all I mean sometimes that's that's all you need but usually you also need to be stimulated by T cell so T helper T cell stimulation and you might say where's the helper T cell stimulate this guy well B cells were also antigen presenting cells so it'll suck this guy in break them out and present him on an MHC 2 complex so that's an MHC let me do it someplace where I can draw it a T cell coming in well let's say this is an MHC 2 complex this guy gets cut up part of him gets presented right here and then a activated helper T cell an activated helper T cell whose variable portion of their T cell respond the receptor is specific to this could come along could come along and activate this character I'm not drawing that receptor well but this is a that right there is a helper t-cell and that is the B cell now once it's activated it starts differentiating and it differentiates it starts cloning itself and it could either turn into effector cells and this is true of B cells or T cells once they get activated they either they keep cloning and they either turn to effector cells or memory cells memory cells stick around a lot longer so that in the future you're gonna have many more of this version of B cells so if you get the same antigen or pathogen in the future the likelihood of it bumping into this type of B cell is going to be higher so the response will occur faster the effector b-cells effector B cells produce they essentially turn into an antibody making machines so they'll say gee this antibody bonds to this antigen that we have in the system now let me just produce a ton of them so it starts building up all of the cellular machinery and it just starts producing antibodies like crazy and I want to point out one thing that my wife pointed out to me when I was she overheard me making the last video and she's a fellow in hematology and pardon a lot of hematology immunology so I definitely have to defer to her she is the expert on this well in the last video I kind of you know very hand waving we said oh you know b-cells once they get activated if they're the effector B cells they produce antibodies I want to be very clear it is only the effector B cells that produce the antibodies and the common term for them the common term for them if someone were to walk up to you and say what what cells in the body are producing antibodies you wouldn't be wrong if you said effector B cells but the common term that people expect to hear are plasma cells plasma cells plasma cells and effector B cells are the same thing but normally when they say what happens to a B cell when it starts producing antibodies they then call it a plasma cell they don't call it a B cell anymore and I want to make that very clear because my wife is like well I have attendings that if they asked me what what selling the body produces antibodies and if you said b-cell they would say no wrong it's a plasma cell or if your unity said effector b-cell they wouldn't be happy they wanted to hear plasma cell that's this is the common term used in immunology and apparently he an apparently Rheumatology circles tonight that I might say my wife is a hematologist no no she's studying Rheumatology I get confused with all the apologies sometimes anyway that's what the b-cell is doing these antibodies can then go attach things and mess up viruses and an antigen well viruses are instances of antigens and bacteria and and and tag them for pick up by macrophages or other types of phagocytes those were the b-cells then you have your t-cells and here I'm going to talk about t-cells a little bit differently than I had in the last few videos just to give a little bit more of a nuance so there's two types of t-cells and you might have be able to say hey there are helper T cells and cytotoxic T cells and you're not wrong but what I'm going to do is do a slightly different differentiation just so that you you are familiar with these terms so there's two types of T cells just like that all T cells have T cell receptors let me draw the T cell receptors T cell receptors just like that but they also have these other proteins on them and some of them have these proteins called I'll just call it I'll draw it like that called cd4 proteins and some of them have I'll do it in a different color and some of them have what's called cd8 CED CED eight so this one right here would be called a cd8 positive T cell it has the cd8 proteins on it and this would be called a cd4 positive cd4 positive T cell I've never used these words before you're like gee where did these coming from now the cd4 receptor is the thing that wants to bind this is the thing that helps to go to the MHC 2 complexes so cd4 t-cells are helper t-cells so this is you know most of the time and I want to make it very clear immunology is a very I mean this field people are discovering things on a regular basis so people are still understanding these things and there's all sorts of special cases but usually when people talking about talk about cd4 positive T cells they're talking about helper T cells so this is normally going to be a helper a helper T cell or you could call it a T helper just like that likewise the cd8 proteins these are attracted to the MHC one complex these are attracted to MHC one you can kind of say this is what brings them to the to the the cells that have the cancer that are that I have expressed antigens on their MHC one complex so most of the time cd8 positive T cells are cytotoxic sido toxic so cytotoxic T cell and oftentimes before a cell gets activated they just describe it as a cd4 T cell or cd8 T cell and then after it becomes for example in the cytotoxic T cell after it becomes activated and starts wanting to kill things then maybe you call it cytotoxic but this is all you know this is all wordplay I think you get the general idea but just to remember what they do this guy we just said it he'll bond he wants to bond to the MHC complex so you have MHC complex plus presenting some antigen plus presenting some antigen this is mhc1 right here we learned in the last video every nucleated cell in the body expresses an MHC one complex so this is the case where something wacky is happening inside this cell maybe a virus isn't infected it maybe it's cancerous it's just it's it needs to die otherwise it's gonna keep producing protein or pre keep producing viruses if it's infected by a virus or otherwise it's gonna keep dividing if it's a cancer and in fact the rest of the body so the cd8 kills infected cells kills I'll just say bad cells because I don't know if you can cancer release into infection kills bad cell cells that are you know if you don't kill them there producing viruses or keep splitting and spreading the cancer while t-cells they're attracted to professional antigen presenting cells so and I always do a gendered excel right here because they're also the best antigen presenting cells and they have CD f's RMH two complexes and it's digested some antigen and it presents it right there and then that activates that activates the helper t-cell and then when the helper t-cell when the helper t-cell all of these guys once they're activated they all go into effect or effect they all start differentiating into effector and memory cells an effect or helper t-cell it does a couple of things it can so when we're talking about helper t-cell it can activate it can activate b-cells and it also releases cytokines and let's say this guy gets activated he'll also start releasing these chemicals which are really those alarm bells that tell other people to really get in gear maybe you know V cells and cytotoxic T cells start proliferating more rigorously actually part of the the T cell act the cytotoxic T cell activation can be assisted or kind of given a be given a boost by these saito by these cytokines so by these alarm bells so this guy is the alarm ringer alarm alarm while the cd8 cells or the cytotoxic T cells within their effector mode they kill cells they kill cells and of course in the memory mode there's just a bunch of copies of these originals around that are ready and more than they were originally were so that in the future if something like this or something like this occurs they're gonna be activated faster because they're gonna be bumped into faster so hopefully that clears up a little bit and I introduced a little bit more topic terminology but I really want to stress my wife's point cuz she said hey you don't want people out there saying b-cells produce antibodies even though it is effector B cells once activated B cells that are differentiated into effector B cells those are what are producing antibodies because when they go to medical school people want to hear plasma cell