in this video, we're going to begin our lesson on a process called affinity maturation. And so here we're asking you guys a question that says how does our immune system ensure mass production of the most effective antibody during an infection. And so one of the answers to this question is through the process called antibody class switching, which recall we talked about before in some of our previous lesson videos and allows B cells and plasma cells to ultimately switch the class of antibody that they will produce and create a more effective antibody class. However, another answer to this question is the process of affinity maturation which is going to allow B cells and plasma cells to continuously create more and more effective antibodies over time. And so what's important to note is that as B cells proliferate and divide it's more likely that mutations will occur. And these mutations can occur in the variable region of the B. C. R. Or antibody genes. And recall that the variable region is the region that is going to control the antigen binding site. And so this can cause changes in the antigen binding site and the ability for the pcR or antibody to bind its antigen. And so ultimately these mutations that occur in the variable region of the B. C. R. Or antibody genes. And the changes that occur in the B. C. R. Or antibodies ability to bind its antigen can lead to a process that we refer to as affinity maturation. And so affinity maturation can be defined as a form of natural selection among B cells allowing for mass production of more effective antibodies over time. And so the way that this process works is that B cells that accumulate mutations in their vcrs that allow them to bind their antigen more effectively are actually going to be a lot more likely to proliferate and divide and create an army of identical clones that combined more effectively. However, the B cells that end up accumulating mutations in their vcrs that allow them to bind less effectively to their antigen are going to be less likely to proliferate and divide and so they will not be able to divide. And so over time as this continues to happen during an infection, the majority of B cells during an infection are going to be able to bind the antigen more and more effectively as time proceeds. And so if we take a look at our image down below, we can get a better understanding of this process of affinity maturation, select naturally, selecting for B cells that bind more and more effectively. And so what you'll notice is that in this image up at the top we have a B cell here that has these B cell receptors or B. C. R. S. And notice that within these B cells there are some green pluses throughout and there are some red pluses throughout as well. And so it's important to note that the green pluses represent more effective B cells and those more effective B cells are going to be more likely to proliferate and divide and then the red plus is actually represent less effective B cells that bind the antigen not as well. And so those are less likely to proliferate. They do not proliferate. And of course the more Green pluses there are the more capable the B. C. R. And antibody is capable of binding its antigen. And the same thing goes with the more Red Plus is the less capable it isn't binding. And so notice that at the very very top what we have is a B cell that is pretty capable of binding to its antigen. And so this B cell that's capable of binding to its antigen is going to be promoted to proliferate and divide. And so notice that as this B cell divides mutations can accumulate in the variable region of its pcr and antibody genes. And so that's going to change the ability for those um B. C. R. S. And antibodies to bind their antigen. And so notice that sometimes the mutations lead to a decreased ability to bind to the antigen. And if that's the case these mutations these B cells that accumulate mutations that lead to less effective binding they are not likely to proliferate and so notice they stop dividing here. However sometimes the mutations will lead to improved ability to bind the antigen. And so notice here we have two green pluses representing um you know mutations that occurred that lead to improved binding and so this one here is more likely to proliferate and divide. And so when it proliferates and divides again mutations are likely to occur. And if the mutations lead to decreased binding ability of the uh pcR or antibody to the antigen again these cells will not be likely to divide and proliferate so they stop dividing. However, if it these mutations lead to yet even better, more effective B cells notice there are three green pluses here, then this one here is going to be more likely to proliferate. And so ultimately what you see here is that this one here can proliferate even more again accumulating more and more improved binding ability over time. And then as these divide again you start to get an army of effective B cells that are more and more effective as time proceeds as they divide and accumulate mutations that allow them to bind better and better and better over time. And so ultimately what we're saying here is that between the process of antibody class switching that we talked about in our previous lesson videos and the process of affinity maturation here that we're discussing in this video over time, B cells and plasma cells are going to be able to produce more and more effective. Be cRS and antibodies over time. And so what this means is that our bodies are going to get better and better at defending themselves from specific types of antigens over time. And so this here concludes our brief lesson on affinity maturation, and we'll be able to get some practice applying these concepts as we move forward in our course. And so I'll see you all in our next video.