Constant and Variable Regions

by Jason Amores Sumpter
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As I've said before, a single antigen can have many different EP itto pops in its structure. B cell receptors will bind to EP itto pops on complete antigens. But T cell receptors bind Tepito piece that have been processed and presented, and the key to this episode binding. And the specificity of the adaptive immune system lies in the genetics of the antigen receptors, and it has to do with what are called constant regions and variable regions. So constant regions, as the name implies, remain constant. And those are parts of the light chain and heavy chain and the alfa and beta chains. Depending on whether you're talking about B cell receptors or T cell receptors, that will be the same in each is a type of that receptor, and here you can see those highlighted in these darker regions. So these are going to be the constant regions or, well, just abbreviate it. See regions, whereas these lighter colored regions chow mark and red just to be extra clear thes air going to be our variable regions or V regions. So how does this all work? How do these variable regions vary from cell to cell? Well, the genes for antigen receptors have many V regions, actually, and they also have other types of regions and thes regions will recombine in unique ways to produce unique structures. This is, uh, kind of the key to how these antibodies and ancient receptors get that specificity to an antigen. So, for example, with light chain actually has about 40 variable regions Azaz well as what are called five joining segments. And between these alone, you can get over to our sorry not over exactly 200 possible combinations. So huge amount of variation there actually, other regions involved that add more variation. But that's kind of beyond the level of understanding that we need. So what happens is as lymphocytes mature, uh, there's genetic recombination of the various regions that will result in unique antigen receptors. And essentially, this genetic recombination is, you know, the crux of the specificity and flexibility of the adaptive immune system. And, uh, what's so amazing? Getting back to that self non self recognition we talked about is that if maturing B and T cells have antigen receptors that bind to self molecules, they are destroyed or deactivated. So the adaptive immune system has a way of guarding against, you know, a T cell or B sell accidentally developing a type of antigen receptor that would bind to a self molecule or molecule Or, you know, a cell of the organism's body. Pretty incredible stuff. And here you can see that recombination sort of modeled out. You know, I don't really want you to worry about the specifics. All you need to know is that there's, you know, a variety of regions that are essentially mixed and match thio create unique receptors. So with that, let's flip the page.