Activation of T Lymphocytes

in this video, we're going to begin our lesson on the activation of T lymphocytes or the activation of T cells. And we need to recall from some of our previous lesson videos that antigen presenting cells or a pcs such as dendritic cells for instance, they actually have both classes of major historic compatibility complexes or MHC s, which means that these ap CS like dendritic cells, They have both MHC Class one and MHC Class two. And because they have both classes of MHC s, they can activate either a naive side, a toxic T cell using its MHC class one Or it could activate a naive helper T cell using its MHC Class two. Now we also need to recall from some of our previous lesson videos that these activated T cells they can then proliferate or multiply to create many many identical clones and differentiate into either an affect your T cell or a memory T cell. And so if you do not recall this information from our previous lesson videos, you should definitely go back and check out those older lesson videos before you continue here. Now that being said because we know dendritic cells have both MHC Class one and Class two and can activate either side, a toxic or helper T cell. We can now look at the two major types of antigens that these dendritic cells could present. And so notice that in our text down below this region right here corresponds with the left hand side of our text of our image down below. And this region of our text right here corresponds with the right hand side of our image down below. And so really there are two major types of antigens that can be presented by dendritic cells. Now, if a dendritic cell presents a harmful antigen on one of its MHC s, either MHC Class one or MHC class two, then that dendritic cell will produce what are known as co stimulatory molecules on its surface. And so these co stimulatory molecules will only be produced by the dendritic cell if that dendritic cell is presenting a harmful antigen on its MHC s. Now these co stimulatory molecules can be defined as molecules that communicate the danger or the significance of an antigen to the naive T cell. And so these co stimulatory molecules are really just going to enhance uh the danger sign. And naive T cells, they will only become activated by dendritic cells that are presenting harmful antigens and presenting those co stimulatory molecules. Now on the other hand, if a dendritic cell is not presenting a harmful antigen. If the dendritic cell is presenting a harmless antigen on one of its MHC s then the dendritic cell will not produce these co stimulatory molecules. And if the co stimulatory molecules are not being produced then the naive T cell is not going to become activated and instead of becoming activated, the T cell will become what is known as a nerd GIC and so the term energetic is referring to a cell that becomes another responsive and this unresponsive or energetic cell will ultimately undergo apoptosis and get rid of the T cell that would generally target a harmless antigen. And what this means is that over time our bodies will not generate an immune response. Two harmless antigens, which is exactly what we want. We do not want to generate an immune response towards harmless antigens. And so if we take a look at our image down below, we can get a better understanding of the activation of these t lymphocytes. And so notice once again, the left hand side of our image over here corresponds to if a dendritic cell presents a harmful antigen on its MHC s and the right hand side of our image corresponds to if a dendritic cell presents a harmless antigen on its MHC MHC. And so if a harmful antigen or immunogen inc antigen is being presented on the MHC s of a dendritic cell. So these little blue cells here are our dendritic cells. Then the dendritic cell will also produce these co stimulatory molecules on its surface. And the co stimulatory molecules you can just imagine are just these molecules that tell the t cells that this is a dangerous and harmful antigen that needs to be addressed and an immune response should be generated. And so when these helper T cells or side a toxic T cells when they detect an antigen presented on a dendritic cell with these co stimulatory molecules. Then these naive t cells will become activated. The naive T cells will activate and then they will proliferate and differentiate into either effect your T cells or memory T cells and carry out an immune response to get rid of this dangerous or harmful immunogen IQ antigen. Now on the right hand side, if a dendritic cell is presenting a harmless antigen like for example normal cytoplasmic proteins for example uh then no co stimulatory molecules will be produced. And so notice that this dendritic cell over here does not have co stimulatory molecules. And without those co stimulatory molecules, these T cells are not going to become activated. So the naive T cells, instead of becoming activated they become a nerd GIC. And again the term energy refers to cells that become unresponsive and they ultimately undergo apoptosis. And so the energetic T cells will undergo a popped oh sis. And what that means is that we are going to get rid of the populations of t cells that respond to harmless antigens. And that's exactly what we want. We do not want t cells that generate immune responses to harmless healthy host cells. We only want our immune cells to generate responses towards dangerous immunogen IQ uh antigens. And so this here concludes our brief lesson on the activation of T lymphocytes and we'll be able to get some more practice applying these concepts and learn even more as we move forward in our course. And so I'll see you all in our next video.

in this video we're going to cover this comic strip for T. Cell activation which we have down below in order to give you guys a fun way to remember when T cells become activated by dendritic cells. And so in this little image or comic strip that we have down below notice that we have two sides on the right hand side over here. This is representing when a dendritic cell presents a harmful antigen to a T. Cell. And on the right hand side over here this is representing when a dendritic cell presents a harmless antigen to a T cell. And so what you'll notice is that the dendritic cell in this image is this little blue guy over here and over here this is Mr Dendritic cell. The helper T cell is going to be up here in the right and then the antigen being presented is going to be either right here or in this image on the right over here. So let's take a look at the one on the left first. And so what you'll notice is that the left one is presenting a harmful antigen. And so we have activation of the T lymphocytes when harmful antigens are presented. And so notice that Mr dendritic over here he is hosting this little sweet shop And here comes virus vic a dangerous antigen with a weapon here. And because virus Vic is dangerous saying give me all of your money notice that the dendritic cell is going to produce co stimulatory molecules to activate the helper T cell. And so the helper T cell says oh no he's clearly harmful and I better activate the reinforcements to generate an immune response and get rid of this dangerous antigen. And so once again we have activation of T lymphocytes when harmful antigens are presented. Now on the right hand side over here, what we have is no activation of T lymphocytes. And this is because a harmless antigen is being presented. And so notice here we again have mr dendritic cell saying hey Officer helper T cell, look what he did and you have over here stu which is a self sell a harmless cell. And so because a harmless cell or harmless antigen here is being presented uh then the helper T cell is not going to become activated. And so notice that the helper T cell Officer th here he's saying oh that's just my son and he is harmless and because he's harmless there's no need to activate and because he's not activating. Of course this means that he will become a nerd chick and energetic means unresponsive and ultimately it will end up uh doing apoptosis. And that will get rid of the T cells that would respond to harmless antigens. And that helps to ensure that our immune systems are only targeting dangerous and harmful antigens and are not targeting harmless and healthy antigens. And so hopefully this little comic strip here is helpful for you guys to better understand T cell activation and we'll be able to get some practice applying these concepts as we move forward and learn more as well. So I'll see you all in our next video.