Which of the following statements is not true? a. An antibody has more than one antigen-binding site. b. A lymphocyte has receptors for multiple different antigens. c. An antigen can have different epitopes. d. A liver or muscle cell makes one class of MHC molecule.

Video transcript

Welcome back. Let's look at our next question. It says which of the following statements about the major history, compatibility complex is true. Well let's think to r content videos and recall what we've learned about the major has to compatibility complex or MHC We know that it comes in two types MHC one and MHC two and that this is part of the body's recognition system of its own cells versus foreign cells preventing it from its attacking itself. So MHC one is the body's self recognition system and it does that because it presents peptides from inside the body's own cells. So proteins found in the body's own cells um when they're just broken down in the normal course of operations, peptide bits from those are presented by MHC one on the outside of the cells as sort of an I. D. Tag saying this is self don't attack this and as a result they are found on all cell types throughout the body because you don't want your immune system attacking any of your different cells in any of your systems. Um They're also highly specific. This is because they are a result of apologetic inheritance. Many different genes together inherited in a co dominant fashion and their polymorphic many different alleles for the genes for the MHC proteins. So as a result even two siblings can inherit a very different array of MHC proteins from their parents because again if you're talking about self recognition, you want that to be a very specific sort of fingerprint to individual Let's look at MHC two proteins then this is the body's foreign invader morning swimming and it's found on cells of the immune system only. And that makes sense because these are the cells that are gonna be encountering and destroying foreign cells. So in that course of action they encounter the foreign cells engulf them, Break them down. And then the proteins that were in those foreign cells, peptide bits of them are presented on the outside of the cells, the immune cells. Just the way MHC one does um as sort of a red flag. So MHC two presents peptides from outside foreign cells. So those uh those proteins that were on the outside of those foreign cells. Um the bits of them are sort of held up as a little example to the body saying these are foreign proteins. Pay attention attack them. They're also highly specific. So similar to the one inherit in a similar way. So let's look at our answer choices. With this in mind. Choice A says MHC one displays antigens found outside the cell. Well, as we discussed below, MHC one is the opposite. It's what presents peptides from inside the cell as part of the body's self recognition system. So Choice A is not correct. Choice B says MHC two displays antigens found inside the cell. Well, again, this is exactly the opposite. MHC two is the one that displays antigens found outside of foreign cells. So choice be not correct. Choice C says an organ transplant can be rejected if cells display different MHC one proteins. Well, this is correct because, again, MHC one presents these proteins from inside the body's own cells as a way of saying this is self. But an organ that's been transplanted from a different individual will have different MHC one proteins and be presenting proteins that are not found in the recipient's body. So, unless there's been a very close match, as we discussed, those MHC one proteins very specific to the individual. So, unless there's been a close enough match, an organ transplant will get rejected if the MHC one proteins on those donated organ cells are too different from the recipient. So, Choice C. Is correct. And then let's just look briefly at choice D. MHC one proteins are found only on cells of the immune system, such as dendritic cells and macrophages. Well, this is incorrect because its MHC two proteins, the foreign invader warning system that are found only on cells of the immune system. So, Choice D not correct. So, again, which of the following statements about the major histone compatibility complexes. True. Choice C. An organ transplant could be rejected if cells displayed different MHC one proteins. Thanks for watching. See you in the next video