 and everybody's going to school. And you know that their schools happen in different places. The B cells are going to school in the bone marrow, the T cells are going to school in the thymus, but they both start out as naïves. Oh, well, let's say the first thing that they do is they're going to pick a receptor. So I mean receptor for T cells, I mean antibody for B cells. They're going to pick their specific little guy now. It's insane when you think about how many different possible antibodies slash receptors can be produced. Think about all the stuff out there that is not you, you would want to have your lymphocytes able to detect or able to respond to. Think about all the different cold viruses that you want your lymphocytes to be able to specifically respond to. It's absolutely mind-boggling. And the way that this incredible diversity is generated is through gene shuffling. So they pick a naïve T cell and a naïve B cell, they actually, they're considered naïve, and that just means that they're not ready to rock yet. They're still babies, but they shuffle their genes and they pick their specific receptor. And once they've committed to their specific antibody or their specific T cell receptor, they go to school. So both of them pick a receptor, they're both considered naïve cells, and then they go to school. Both of them participate in negative selection school. Maybe I should say negative selection class. One of their classes they have to take is negative selection. And this one involves just making sure that you do not bind to self. And if you pass this class, then you are going to be self-tolerant. So if you pass, you're self-tolerant. If you don't pass, that means that you actually stick to self-molecules. Your receptor binds to you, and that's bad, right? So guess what happens? 95% of the naïve lymphocytes fail. And guess what they have to do? They don't go through necrosis. They go through apoptosis. They have to commit suicide. Like, if you don't pass this class, you're done. You have to commit controlled cell suicide, and the game is over for you. You picked a bad receptor. So 5% pass rate where, yeah, they are self-tolerant. This happens with both of them. I should have put it in the B cell category so that we had a little bit more room, but I guess it makes sense to keep it in the T cell or in the middle because it is related to both of them. T cells. T cells don't get to call it the end of the story there. They actually carry on, and they have to go to positive selection class. And in positive selection class, you check to make sure you can bind to MHC platforms. What? So does that give you a hint about what T cells are actually going to do? I hope so. Positive selection class means you can bind to MHC. Now, the fact is that some of them need to bind to MHC2 to get activated. Some of them need to bind to MHC1 to carry out their actual function, like why we even have them in the first place. So if they pass positive selection school, then they are considered immunocompetent. And we're going to come back to this, and we're going to remind ourselves of this because right now you might be like, dude, why is it different? And why do I care if they're immunocompetent? They have different ways of becoming mature. Right now they are at school, and if a big if, if they passed negative selection school, then they are self-tolerant, and if they passed positive selection school, then they're immunocompetent. They're still naive cells. They're still naive lymphocytes. However, they have functional receptors. So now they can go out and at least patrol, 5% of everybody that we sent to school is going to go out because they have graduated, and they can go out and patrol the area. What do you think they're patrolling for? They're patrolling for their specific antigen. And how they do that is dependent on whether they're B cells or they're T cells. So in the next section, we're going to look at MHC2 because we talked about MHC1, everybody has it. Everybody posts their news on MHC1, but MHC2 is required for activation of a naive lymphocyte. So if you're naive, you can't just find your antigen and then be like, awesome, nuclear warfare, let's do this. There's like a whole bunch of checks and balances, thank goodness, because they're babies. They don't know anything yet. And so there have to be other people to activate those naive lymphocytes before they're mature and they can carry out the actual effects. So let's look at the MHC2 platform and see what role it plays in the activation process.