 Remember that the MHC, the major histocompatibility complex, MHC, is basically a protein platform that provides information about what's going on inside a cell. And I want you to take a second to visualize this. All cells have MHC1 platforms except not red blood cells. Did you hear that? That's actually whoa. That's the reason why you can do blood transplants, blood transfusions, between they're easy. I can donate my blood and 40% of the United Statesian population can accept my transplant. That's unbelievable. Not 40% of the population could accept a heart from me or a kidney from me or an eyeball or skin from me, a much smaller percentage. And it's because of these MHC1 platforms. That actually, you have to match MHC1 platforms that I want to trade body parts with someone. Because my immune system goes, dude, that's my MHC1 platform. All my cells have it except for my red blood cells. If somebody else's MHC1 comes in, I know that that's not me and I will attack it and kill it. So MHC1, remember, it's, let's just say we ate, we have some little, here's the little virus. And it's inside our body. We're doing our thing. Let's just go ahead and throw that virus into a vesicle. We find it. We're like, let's digest this thing. I don't know what this is in here, but it's what's happening inside me. So I feel like giving a big woof woof to the world and letting them know what's happening with me. This little vesicle of virus part is digested, so broken up into little pieces of virus. And then the little pieces of virus, after it gets broken up by the vesicle that's digesting it, those pieces of virus are sent to the endoplasmic reticulum. So they go to the endoplasmic reticulum. Now think, what happens in the endoplasmic reticulum? What is the endoplasmic reticulum? Remember, this is where proteins are processed. Proteins that are built in ribosomes can be folded and made into their proper shapes in the endoplasmic reticulum. So guess what happens with these virus parts? The endoplasmic reticulum says, I got you, dog. Let me take that virus part that you have. And I have a little MHC platform right here. And I'm building it as we speak, so I'm just going to add that little virus part to this platform inside the endoplasmic reticulum. Does anybody remember? I wish you were here so that you could holler out. Hala, hala. So maybe remember what happens next. Remember how the endoplasmic reticulum like pinches off and sends a little vesicle to the Golgi body? That was that little stack of pancakes. And so the Golgi apparatus is going to be like, I got this fantastic little bubble of MHC. Now look at what happens. The MHC is actually embedded in, I changed my mind about how I want to draw that, it in its own little vesicle that goes to the Golgi into another little vesicle and guess what happens to it. I'm just going to leave it in this vesicle. This isn't going to work for how I did it. I had to do it the first way. Oh, you got this dog pounds because watch. I'm going to go like this. I don't even think I need to send it to the Golgi apparatus. And now I think this is going to work. Watch. I'm going to take it up here and I'm going to exocytose this. I know that I cannot draw this well. But look, I'm going to go like this and I'm going to exocytose my little platform, my little platform, which was just sitting in here, right? And it had the little piece of virus attached to it and now what's on the surface of my cell? My platform, my MHC1 platform is on the surface of my cell and it has that little virus piece in it. Okay, you got it? Somebody's going to come checking that to say, now natural killers we know will come and check that and they can identify general problems. But the acquired immune response, your B cells and your T cells, actually your T cells are going to come along and they're going to be able to read this and know, uh-oh, I think there's a virus in there and they're going to do their thing. Everybody except red blood cells have these platforms to let you know what's going on inside. Now MHC2, not everybody has MHC2 and MHC2 is required to activate our acquired immune response.