 Hey everybody, Dr. O. In this video we're going to talk about all the different types of T cells. So T cells are a type of lymphocyte, we've covered the natural killer cells already, the NK cells, we'll cover the B cells here in the next video. So here's the kind of story I like to tell when we're dealing with our T cells. So we have the helper T cells at the top there, what are called the CD4 T cells. Those are going to be the generals because their job, they don't kill cells directly, but they activate and direct other cells to do the work for them. So they're going to be the generals. Then next we have, let's, let's get down to the cytotoxic T cells or the CD8 T cells. These are going to be the soldiers. These are the ones that directly kill other cells and what's called cell mediated immunity. Then in the middle you have what are called the regulatory T cells. You'll hear them called T regs as well. I'll put that on the screen. I personally still call them suppressor T cells. That was their name for a while, but regulatory T cells or suppressor T cells consider them the Peace Corps. So we have the generals that direct the battle. We have the soldiers and now we have the Peace Corps. They're the ones that try to keep the peace or make sure that there's not too much conflict. So they keep your immune system getting out of hand, right? Which because of too much immunity is a terrible thing. Can lead to hypersensitivities, anaphylactic shock, autoimmune conditions and the like. All right. So other than the T regs, I still want to talk more about the helper T cells and the cytotoxic T cells here, but I just want to introduce them all in one place. Let's go ahead and dive in. The CD4 positive T cells, those are your helper T cells and the CD8 positive T cells, your cytotoxic T cells. So CD4 is going to matter. I mean, there's different receptors basically, but the CD4, you're going to hear that if you ever learn about HIV. So HIV specifically infects and destroys the CD4 positive T cells and it infects the helper T cells. So someone with HIV is getting their T cells checked. They're looking for these, the helper T cells. And if the T cell count drops below 200 cells per microliter of blood, then you, you now have eights. HIV becomes eights. So here just real quickly, you see the CD4 positive T cell on the top, not only does it activate and direct the CD8 positive T cell there in the corner, but it also activates your B cells. So this, the helper T cell is the general responsible for both halves of your immune system. The cell mediated immunity by directing cytotoxic T cells to kill other cells and antibody mediated or humoral immunity by activating B cells to become plasma cells and make antibodies. Here you see what a naive helper T cell. So naive just means it's a fully functional immune cell, but it doesn't have a target yet. It hasn't been told what to look for. So once a naive helper T cell has been given a mission by an antigen presenting cell like you see here. Now it's going to become either a TH1 cell, a TH2 cell or a memory helper T cell. So I don't make a huge deal out of this, but just so you know, the TH1 cells, they're going to be the ones that activate the other types of T cells, your cytotoxic T cells and also cells like macrophages. So they're going to have those cell mediated immunity related cells be, be activated. The TH2 cells are the ones that are going to activate your B cells to become plasma cells and make antibodies. And memory helper T cells are going to be there for the next time you see the same antigen. So the next time you're exposed to something, that's how we develop immunity. We have memory cells of all different types that are waiting to start this response more quickly the next time. All right, then same pictures before, but now we're looking at those CD8 positive T cells. Instead of being the general that direct to the combat, these are the soldiers. And they're going to actually find their targets and they're going to attack and destroy their targets. They use very similar chemicals, very similar to methods to the natural killer cells, but they have a very specific target. NK cells or natural killer cells, they're involved in immunological surveillance because they just know that something's wrong with a cell. The cytotoxic T cell has a very specific target. Once it finds it, as you can see there, it attacks and destroys that cell using the same chemicals like perforins, granzymes, these types of things that are going to have this cell basically implode or kill the cell directly without letting it leak all of its contents, hopefully into the environment because that could actually help these pathogens spread infections. Here you see the same thing, a naive T cell is given its mission, it's given a wanted poster and says, this is the cell you're looking for. And then some of these cells are going to become activated cytotoxic T cells and go and attack and destroy that enemy, some are going to become memory T cells which are involved the next time you're exposed to something. Okay, so those are all the different type of T cells you're supposed to know. A lot of important information here, hope this helps, have a wonderful day, be blessed.