If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:9:16

Cytotoxic T cells and MHC I complexes

Video transcript

everything we've discussed so far involved recognizing and tagging or engulfing shady things that were found outside of cells so outside of cells we've seen things like a B cell a B cell has its membrane membrane bound antibodies its membrane bound antibodies maybe one of these might might recognize something shady out in the outside of the cell and of course this part over here as we know these they all have a variable portion right over here so this is specific to this shady thing then this will be engulfed and then parts of it parts of it will be attached to an MHC 2 complex so let me do that in a different color so an MHC 2 complex and then that will go to the surface that will go to the membrane of the cell to present itself so that's an MH 2 MHC 2 complex and so it has a little bit of the little little piece of this shady thing out here and we call this little shady peach this is an antigen this is an antigen presenting cell here and then we've seen is especially if this is a b-cell then a helper T cell that also has a variable portion that corresponds to that corresponds to this specific antigen so this would be a helper T cell right over here so this is a helper T helper cell when it recognizes then it'll start dividing into memory helper T cells and effect our helper T cell so the effector helper T cells essentially ring the alarm bells and start kind of accelerating the B cell replication I guess you could say that the B cell activation and and the theory is that this is kind of a double handshake process but once again this is what's occurring outside of cells so when we found stuff outside of cells we engulf them and then we presented them on MHC 2 complexes mhm see two complexes so now you're probably thinking well yeah I mean that's the outside of cells but you know there's MHC - there's these helper T cells but we've also referred to cytotoxic T cells what do those do and we've also if there's MHC - there's probably an MHC one complex what does the MHC one complex do and if we're you know we can recognize shady things that are happening outside of cells but don't shady things sometimes happen inside cells and what do we how does our immune system respond to that and actually as you can imagine all of those all of those things will be answered in the rest of this video so let's think about what's happening let's think about what happens when shady things start to happen inside a cell so for example for example it might not even be due to a virus or due to way back to some type of bacteria it could be the cell itself has gone awry so let's say that this right over here is a cancer cell so it's had some mutations it's starting to multiply like crazy so this is a cancer cell and the cancer cell because it had mutation it's going to produce it's going to produce some weird some weird proteins so these cancer cells are going to produce some weird proteins so every every every cell with a nucleus in your body and that's pretty much every cell except for red blood cells has the has MHC one complexes and the point the whole point of the MHC one complex is to but is to bind to shady things that are produced inside of the cell shady things that are produced inside of the cell and then present them to the membrane so even a malfunctioning cancer cell should be doing this so then it will so this MHC one complex is bound to this two bound to this these strange proteins that are produced by the the mutations inside of the nucleus and then it can present them and then it can present them and so what you could imagine what the appropriate immune spot response should be these things these cancer cells these cancerous cells should be killed and actually let me label this properly so that was MHC 2 you're presenting an antigen that was found that was initially found outside of the cells engulf with and taken out MHC 1 MHC 1 it's binding to shady things inside the cell and then presenting it out now this thing should be killed now as you can imagine what's going to kill it well that's where the cytotoxic T cell comes into the picture so the cytotoxic T cell is going to have so that's a receptor right there it'll have a variable portion that's specific to this type of an antigen and so it'll bind there and then once it does that it says oh boy there's just all this shady stuff here these shady proteins that are in produce this this cell and all the other ones like it need to be killed and so the cytotoxic T cell will begin to replicate once again like other other types of immune cells it's going to replicate into the into the memory cells just in case this type of thing shows up ten years in the future and also the effector cells so this is memory and also effector and also and also affect your cells effector cytotoxic T cells and as we always know the effector version is the thing that actually does something it starts to actually affect things and what it is going to affect it is going to start binding to things that are that are presenting the same antigen on top of as part of their M R on top of their MHC one complex so this character right over here so it's presenting that same antigen it's presenting that same antigen on this MHC one complex and remember the variable portions need to match up so let's say that this is this is an effector cytotoxic T cell an effector cytotoxic T cell and actually let me draw it a little bit a little bit different so let me draw it like this this is effector cytotoxic T cell its receptor it's variable portion is the one that's compatible with this antigen that's being presented right over here so let me just label this again this is the MHC one complex this is an effector cytotoxic cytotoxic T cell so I put the C there for cytotoxic and what it does is essentially kind of latches on to the cell that needs to die and it does it it not only just has this receptor interfacing with the MHC one complex but it actually has a whole series of protein and I'm proteins and I'm not drawing this to scale really this would be much smaller relative to the scale of cell that essentially latches on between the two and I'm not going to go into detail but essentially forms what you could call an immuno synapse which is kind of where the two things are interacting with each other and so when it identifies this and says okay I need to kill this thing or essentially I need to make this thing kill itself it starts releasing all of these molecules so it can release molecules like perforins so it'll release these perforins which will essentially cause gaps or holes to follow to fit to form in the in the in the membrane of the cell that needs to die and it could release other things like granzymes that can go in and essentially cause this thing to kill itself so the whole point of this video is to appreciate I guess what we haven't talked about yet we had already talked about what happens when you identify shady things outside of the cells and then how you can kind of bring them in and then present them and then use that to can further activate the immune response now we're talking about identifying shady things inside the cell those get presented by MHC one complexes and then the cytotoxic T cells recognize them and then force the cell to kill themselves and this wouldn't just be cancer cells this could also apply to a cell that has already been infected by a virus so for example a cell like this already so that's its nucleus it's already been infected by some virus it's already been infected by some virus so it's hide the virus has hijacked the cells replication machinery in order to replicate itself and so the proper immune response is hey look I'm uh I'm uh I'm a virus making machine I I should kill myself so so it'll take some Italy antigens that are being produced inside of by virtue of by the fire is there going to bind to MHC one complex --is to MHC one complex is so pieces of the virus we're going to bind to MHC one complex is and then they're going to be presented on the surface they're going to be presented we do it this way presented on on the surface so this exact process can happen again
Biology is brought to you with support from the Amgen Foundation