 All right, I get a little sad when I talk about natural killer cells. First of all, I get sad because it makes me think of the movie Natural Born Killers, which was quite possibly one of the most disturbing movies I've ever had the unpleasantness to have to watch. I don't want to think about it too much. So I will try not to think about that. Natural killer cells are a type of lymphocyte. Oh dear. They're a type of lymphocyte that not very many lymphocytes are natural killer cells. I'm going to draw you a picture of a lymphocyte because this will remind you lymphocytes were those white blood cells that have very large round nuclei. When you're doing white blood cells, when you're doing blood histology, you look in the microscope and you see these awesome white blood cells and you get really excited because you think you found a big lip of cytoplasm and that was just the dark nucleus that you see. Lymphocytes have a big round, moony nucleus and sometimes they don't have much else inside their cells. Lymphocytes are responsible for the acquired immune response. So we're going to talk about them in great detail in the next lecture. Natural killer cells are the exception. Only 2% of lymphocytes are natural killer cells and here's what they do. They go around and they check you. So they look at the self cells and here's the scoop. I'm going to give you just a little heads up. We're going to have an entire section on this in the next lecture on the acquired immune response. But this is one of your cells and I'm so excited about this. I can hardly stand it. This is like the whole reason that I teach the immune system so that I can tell you that all of your cells have Facebook, true story. All of your cells have these protein platforms. I'm not joking. I am not making this up called MHC or Major Histocompatibility Protein Platforms. MHC platforms are basically the place where your cells post status updates about what's going on inside them. So if this cell, this U cell was like, dude, this is great. I just ate a chocolate cake. It's going to post little pictures of chocolate cake. Look, I'm going to put a cherry on top of my chocolate cake. That's chocolate cake. And little pieces of chocolate cake are going to be posted on the MHC platform. Now, natural killer cells are coming along and they check everybody's MHC platforms. They're like big brother. They're coming around and they're going, okay, what's going on inside there? And we're going to monitor your Facebook posting and guess what we're going to do if we don't like it. Because guess what? If you posted, like, you posted, look, watch what I'm going to post. Uh-oh. What is this? Uh-oh. Tell me that you know what that is. It's a virus. If you were infected by a virus and you're like, oh yeah, I feel kind of funky and I don't know what's wrong with me, but I'm going to post pieces of this virus that I have on my MHC platform. Dude, natural killer is going to come along and be like, check your MHC, here he comes. He goes, uh-oh, that ain't you, dog, that ain't you. And he is going to make you commit suicide. Terribly sorry, we have rules here. If you're going to post crap like this, we will force you to kill yourself. And so natural killers initiate, initiate apoptosis. Apoptosis is sell suicide. What? So be careful what you post on your Facebook platform if the natural killers are around, because if you, now, all jokes aside, if you post information about a virus that has infested you, it's probably in everyone's best interest to kill yourself. How awful is that? My analogy breaks down tragically at this point, so please do not take offense. Because if you don't kill yourself and you are virus infested, this little cell is going to be hijacked by the virus and is going to produce like bajillions, frenillions, gazillion viruses. The viruses are going to fill up the inside of the cell so much that guess what the cell is going to do? It's going to pop. Instead of having controlled death, suicide, taking one for the team, thanks dog pound, you're going to explode, you're going to die anyway, and now you've exploded and let all baby viruses out into your body. And so you've got it. So natural killers come along, you know? It's a dirty job that somebody has to do it. If you're infected, we're going to make you kill yourself so that it is kind of under control that you don't have to infect everybody else in the process. All right, sounds like a good strategy. It works now. We're going to talk about the last innate strategy that happens or that's facilitated by the innate immune response. It's facilitated by more chemicals and that's fever.