MHC and Antigen Presentation

Hi in this video we're gonna be talking about MHC and antigen presentation. So MHC molecules are called major historic compatibility complex and what they do is they bind to antigens and activate cells and T cells. The things that express MHC can be, you know, part of the innate immune system, part of the adaptive immune system. But essentially this is a major way that antigens are presented in order to activate them. Now there are two classes. This video is going to focus on Class one and then the next one will focus on Class two. So Class one is responsible for activating T. C cells. So remember these are side a toxic T cells and so um it has this structure, it consists of a single polyp peptide chain and this single chain is going to be attached to a peptide called a beta two micro globulin. And um there is the combination of these to make a single peptide binding site that fits around an 8 to 10 amino acid peptide sequence on the and again. So here are the six steps of how it happens first. You have a pathogen, This is going to be an intracellular pathogen. This is a big important part and a major differentiator between the class one and Class two. So the intracellular pathogen, it's going to be present in the side of soul. So how did it get there? Well the intracellular pathogen could be from a cell that's been infected and it's just already inside it could be a cell that has you know, is maybe expressing viral genes um that are just produced in the cell itself. But either way there's an intracellular pathogen. This pathogen needs to be destroyed. So it's targeted via ubiquity and and passed passed through the protea zone for degradation. Remember the protozoan ubiquitous pathway that we talked about? So this is how it's destroyed and this chops it into little pieces. Then these little antigens, These little pieces are transported into the er you don't need to know this but there's a special complex that does this called the tap complex. And then once it's in the er it binds to the MHC Class one molecule and then eventually that's gonna travel to the plasma membrane be expressed and then that an engine and MHC complex will activate the side of toxic T cells. So here we have so here we have a pathogen. I'm supposed to have an agent, a pathogen and it is destroyed through the protease own. Then these little pieces travel into the er Where it complexes with MHC Class one that then travels to the surface and activates T. C. Cells. So that is the Class one. Let's now turn the page

Okay, so in this video we're gonna be talking about the Class two major historic compatibility complex or MHC. And this is responsible for binding to an agent and activating the T. Helper or the T regulatory cells. So the structure for the class two is a little different. This consists of a hetero dime er that are both encoded by MHC genes. So these are two MHC genes that form a hetero dime. Er um it also has a slightly longer peptide binding site than the class 1 12 to 20 amino acid and this is going to combine the entire peptide. So this is done by um said six but this is really seven steps. So the first step is we have an extra cellular pathogen. So this is a super important difference between the two. This pathogen is going to be taken up by the cell. Then the pathogen after it's taken up, moves to the license zone for destruction. So it's also a big difference. Then the pathogen is going to be degraded in the license zone into the tiny peptide fragments. Antigens. Then at the kind of at the same time the class two molecule is made in the er and complex with a small protein called li. Then this travels to the light zone where the antigen is lee is then cleaved to form clip and then clip is eventually replaced with the antigen in the life zone and then the complex moves to the cell surface. So let's look at this example. So we have a pathogen, it's extra cellular, it is internalized and it travels to the life zone where it's degraded into these small pieces. At the same time you get the MHC Class two which is made in the er let me use a different color made in the er and it's complex with lee. This is like blue protein here. This complex with it attached to lee moves to the listen zone where that is cleaved to form clip and eventually replace to form with the antigen. And then this will travel um to the cell surface where it activates T. Helper and T. Regulatory cells. So that is how Class two works. Which you can see some major differences including the extra cellular pathogen. The license um destruction the clip and lee. Um And the type of cells that are activates. So with that let's now turn the beach.