in this video, we're going to briefly review the differences between Cida toxic and helper T cells and we're going to do that by completing all of the interactive blanks in this table down below. And so notice on the far left we have a column this is type of T cell and recall there are two main types of T cells. The first are the sido toxic T cells or TC cells for short and the second are the helper T cells or the T. H cells for short. Now notice that this entire row right here applies to Cida toxic T cells and this entire road down below applies to the helper T cells now recall that in terms of the C. D marker, psycho toxic T cells have a cd eight marker on their surface. And so that's why Cida toxic T cells are sometimes referred to as cd eight cells. Whereas helper T cells have a cd four marker on their surface and they're referred to as cd four cells. Occasionally. Now, in terms of the antigen presenting proteins, recall that psycho toxic t cells are capable of recognizing and responding to antigens presented on MHC Class one molecules. And on the other hand, helper T cells are capable of recognizing and responding to antigens presented on MHC Class two molecules. Now recall that the MHC Class one molecules are going to be found on all nuclear gated cells and this is partially what allows for Cida toxic T cells to target all of our nuclear gated cells Now. On the other hand, MHC Class two molecules are not found on all nuclear gated cells. Instead, they're only found on some of our cells, specifically the antigen presenting cells such as dendritic cells, Macrophages and B cells. Now in terms of the antigen source, notice that MHC Class one molecules are going to be presenting endogenous antigens or in other words antigens that are inside the target cell. So for example, antigens from a virus that is infecting the inside of a target cell. Now, MHC Class two molecules on the other hand, they present exogenous antigens or antigens that are going to be outside of the target cell initially. And so you can see here these antigens originated from outside of the target cell. Now they can be internalized and process and then presented on these MHC Class two molecules. But again these antigens would have originated and be causing harm on the outside of cells. And notice that in terms of the target cells that once again because MHC class one molecules are on all nuclear ated sells, it allows Cida toxic T cells to pretty much target any of our nuclear gated cells which is practically all of our cells now. On the other hand, MHC Class two molecules are only found on those ap CS antigen presenting cells and it turns out that the helper T cells they mainly are gonna be targeting the ap CS that include B cells and macrophages. And in terms of the functions recall that Cida toxic T cells their function is to induce target cell apoptosis inducing apoptosis of infected host cells causing a cell that is infected with an intracellular pathogen like a virus to undergo apoptosis in order to eliminate the infected cell but also eliminate the pathogen, the intracellular pathogen. Now helper T cells, on the other hand, they do not induce apoptosis. Instead they're all about activating or stimulating a target cell to improve that target cells immune capabilities and so they can target B cells and target macrophages to help activate those B cells and macrophages and again either lead to an immune response or lead to an improved immune response. And so this year concludes our brief review of psycho toxic versus helper T cells. And again we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video

in this video we're going to briefly cover our comic strip for T cell functions. And so notice that down below we have this portion of our image that corresponds to the same comic strip that we covered in our previous lesson video. And so here in this image, we've only added this little section over here and this section here in pink is what is new in this video. And so just to refresh our memories about this comic recall that uh T lymphocytes will not be activated if harmless antigens are being presented. And so notice that are dendritic cell over here is presenting an antigen that is harmless. It's Little stew which is a self sell, a harmless antigen. And so notice that the T cell here recognizes that this is a harmless antigen that there's no need to activate. And so it remains in an energetic or unresponsive state. And so it will not generate an immune response towards harmless antigens. Now, on the other hand, if a harmful antigen is being presented such as virus vic right here then the dendritic cell is going to produce co stimulatory molecules that will activate the T lymphocytes. And so notice he's saying here he is harmful and because this is a harmful antigen, it is going to be generating an immune response. So it activates reinforcements And ultimately and our new part of the image the activated T lymphocytes are going to be able to create a an effective immune response to ultimately eliminate the threat. Uh And so by eliminating the threat here, what you can see is that these other immune components have been assembled here. We have the cd eight cells, we have the cd four cells And uh the cd four cells can uh you know activate macrophages and B cells and things of those nature to generate an effective immune response to eliminate the pathogen and destroy the pathogen so that it no longer is effective and cannot cause us harm. Now, as we'll talk about more moving forward in our course, we're going to learn how sometimes our immune system can cause unintentional harm to our own self. And so that is not a good thing about our immune system. Yes, it's very effective at eliminating pathogens but occasionally it can cause our own tissues harm. And so we'll be able to talk about that aspect of our immune system more as we move forward in our course. But for now what you can see here is that again, t lymphocytes are not activated with harmless antigens. They're activated with harmful antigens. And once those t lymphocytes are activated they will work to eliminate the threat. And so we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video