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 Mister Dendritic Cell. The helper T cell is going to be up here on the right, and then the antigen being presented is going to be either right here or in this image on 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 Mister 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 the dendritic cell is going to produce costimulatory 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 Mister Dendritic Cell saying, "Hey, Officer Helper T Cell, look what he did." And you have over here, Stu, which is a self-cell, a harmless cell. And so because a harmless cell or a harmless antigen here is being presented, then the helper T cell is not going to become activated. And so, notice that the helper T cell, Officer T_H 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 anergic. And anergic means unresponsive, and ultimately, it will end up undergoing 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.