in this video, we're going to begin our lesson on a process known as antibody class switching. And so first we need to recall from some of our previous lesson videos that when plasma cells are first formed from B cells that differentiated into them, these plasma cells are initially going to begin producing and secreting the antibody class known as I G. M. And so I G M is the very first antibody class that is going to be produced initially. However, as activated B cells continue to multiply and proliferate some of those activated B cells are going to undergo a process known as antibody class switching. And so antibody class switching as its name implies, is going to allow for plasma cells to switch the antibody class that they are producing and secreting. And more formally we can define antibody class switching as a process characterized by changes in the D. N. A. Of an activated B cell that ultimately allows its plasma cell to change the antibody class that it is producing. And so uh plasma cells that descend from B cells can go from secrete ng the antibody class I. G. M. To secrete ng the antibody class I. G. Through the process of antibody class switching. Now, antibody class switching once again occurs via changes in the D. N. A. And so it occurs more specifically via genetic rearrangement of the DNA encoding the antibodies constant region. And so recall that we discussed the constant region of antibodies when we discussed the structure of the antibody. And so what's important to note is that even after antibody class switching when plasma cells go from secreted by GM. To I. G. G. That new antibody class still maintains the specificity for the same exact episode of the same exact antigen. And this is because the variable region of the antibody is unchanged. And so the I. G. M. Class of antibodies secreted by these plasma cells would bind to the same exact epitope and same exact antigen as the I. G. Class of antibodies secreted by those same plasma cells that have descended from those activated B cells. And so um what happens in this antibody class switching process which we'll get to discuss more in our image down below is that the deleted gene segments of the constant region are not going to be expressed. And it's really the gene segments that remain for the constant region that are first in line that are going to be expressed. And so if we take a look at our image down below we can get a much better understanding of this process of antibody class switching. And so notice at the very top of our image here what we have is an activated B cell that is now multiplying and proliferating and dividing to create more activated B cells. Now sometimes when these activated B cells divide there is no loss of their DNA segments. And so in those cases these activated B cells when they divide there's going to be no changes to their D. N. A. And when there's no changes to the D. N. A. What that means is there's no changes to the constant regions. And so notice that here we have the five different classes of antibodies. And notice that initially all of these B cells are going to be programmed with all of the genes for these five different classes of antibodies. However it's only the gene segment that is first in line that is going to be expressed and by first in line we mean here furthest to the left in this image. And so it's the I. G. M. Class that is actually going to be programmed to be first in line. And so what this means is that it is the I. G. M. Class of antibody that is going to be produced initially. And so notice here we have a plasma cell that is going to be producing and secreting the I. G. M. Class of antibody which you might recall is a pen Timur. As you see here that consists of five identical subunits. Um However, although I G. M. Is the very first class of antibody produced by the plasma cells that descend from the activated B cells again as these activated B cells divide and proliferate some of them will undergo the process of antibody class switching, allowing them to switch uh the antibody class from my Gm to any of the other types of antibodies. And so what you'll notice is that in the process of antibody class switching described more on the right hand side of this image uh there is going to be the loss of very specific DNA segments coding for the constant region of the antibody. And so what you'll notice is that the variable region once again is unchanged. As we discussed up here, variable region of the antibody is unchanged. However, the constant region which is going to differ from one antibody class to another. Uh some of those regions may be deleted. And so here in this specific example we're showing you that it's the region for I. G. M. And I G. D. That are both being deleted in this particular example. And so when that happens when I G. M. And I G. D. Are deleted and removed, the only segments that remain R I G I G. And I G A. And so you can see those that are remaining down below right here. And what you'll notice is that again it's the gene segment that is first in line that is going to be expressed. And so in this case I. G. Is the first gene segment furthest to the left. And so that means that I G. G. Is the class of antibody that is going to be secreted and produced by this plasma cell. And so here you can see a plasma cell that is secreted in the I G. G. Class of antibody. And so this is how antibody class switching can occur. Notice that these first descendants of plasma cells initially were secreted by GM. But as time goes on, the plasma cells that descend can switch the class of anybody that they are producing and secreting. And so once again here we're saying that the antibody gene that is again first in line is going to be expressed and secreted by the plasma cell that descends. And so this year concludes our brief lesson on antibody class switching and how antibodies and and how plasma cells can go from initially secreted by GM to secreted another class of antibody like for example I. G. And so we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.