T cells and B cells become activated when they're antigen receptors. Bind the appropriate Auntie Jen, and basically these lymphocytes just flow and hang out around the lymphatic system, the blood, the spleen and some even in the skin, and that mucosal associated lymphoid tissue. Until they get a match. It's It's kind of a scattershot approach that the adaptive immune system takes. They try as many different things as they can, and if they get a hit, that's great. But if cells don't encounter the proper EP itto within a certain timeframe, they'll actually die. Cells will eventually die, and if they do encounter the right Apatow, though, they will basically clone themselves. They'll divide and turn, create a what's called a clonal population just a big group of Selves that are clones of them. And this is part of what's called clonal selection theory. Essentially, this is an idea that says antigens will basically select the lymphocytes by, you know, the lymphocyte. Just encountering the right Auntie Jen, the antigens will select the lymphocytes to divide into that clonal population. So basically, you know, if they are activated, they will make a you know, many clones and, uh those clones will become what are called defector cells and memory cells. And before we talk about what those are, I do want to point out that sometimes, uh, lymphocytes that have not been exposed to an antigen yet are called naive lymphocytes. So that's just a mature lymphocyte that hasn't yet been exposed to It's appropriate. Auntie Jen. Now affect our cells are gonna be the short lived but fast acting, um, cells of the adaptive immune system. They're going to take immediate action against the pathogens that are present. Memory cells are gonna be longer living cells. They actually will continue Thio divide at a low rate thio keep up a population around, and they're going to just hang around and be used to fight future infection. So their job is not to take action against these current pathogens. Invading their job is to wait and see if they come back and then mess those dudes up. And here you can kind of see unexamined of how this sort of clonal selection it goes down. We have these, like naive lymphocytes. This particular one has a match. So it's going Thio clone itself a bunch. Uh, these other guys, they didn't get matches, so they're gonna die out. Sorry. You know, brutal in the immune system. And this clonal population is going to divide between some memory cells. And some affect your cells that you can see behind me. All right with that, let's flip the page.