Antibody Class Switching - Online Tutor, Practice Problems & Exam Prep

Antibody Class Switching

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 IgM. And so IgM 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 DNA of an activated B cell, that ultimately allows its plasma cell to change the antibody class that it is producing. And so plasma cells that descend from B cells can go from secreting the antibody class IgM to secreting the antibody class IgG through the process of antibody class switching. Now antibody class switching, once again, occurs via changes in the DNA. And so it occurs more specifically via genetic rearrangement of the DNA encoding the antibody's 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 secreting IgM to IgG, that new antibody class still maintains the specificity for the same exact epitope of the same exact antigen. And this is because the variable region of the antibody is unchanged. And so the IgM class of antibodies secreted by these plasma cells would bind to the same exact epitope and same exact antigen as the IgG class of antibody secreted by those same plasma cells that have descended from those activated B cells. And so, 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 DNA. And when there's no changes to the DNA, what that means is there's no changes to the constant regions. And so notice that here we have the 5 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 5 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 IgM class that is actually going to be programmed to be first in line. And so what this means is that it is the IgM 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 IgM class of antibody, which you might recall is a pentamer as you see here that consists of 5 identical subunits. However, although IgM 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 the antibody class from IgM 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, 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, some of those regions may be deleted. And so here in this specific example, we're showing you that it's the region for IgM and IgD that are both being deleted in this particular example. And so when that happens, when IgM and IgD are deleted and removed, the only segments that remain are IgG, IgE, and IgA. 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, IgG is the first gene segment, furthest to the left. And so that means that IgG 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 secreting the IgG class of antibody. And so this is how antibody class switching can occur. Notice that these first descendants of plasma cells initially were secreting IgM, but as time goes on, the plasma cells that descend can switch the class of antibody that they are producing and secreiting. 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 here concludes our brief lesson on antibody class switching and how antibodies and how plasma cells can go from initially secreting IgM to secreting another class of antibody, like for example, IgG. 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.

Class switching occurs when which of the following scenarios occur?

• A. The deletion of specific heavy chain genes in the B cell DNA.
• B. Genetic variation of the variable region in an antibody gene within a B cell.
• C. Large deletions of genes encoding the variable region of antibodies in B cells.
• D. Gene rearrangements in a T cytotoxic cell causing the cell to become a T helper cell.

Which lymphocyte is responsible for inducing class switching in B cells?

• A. Regulatory T cells.
• B. Cytotoxic T cells.
• C. Helper T cells.
• D. Memory T cells.

Why is class switching of antibodies during an infection important for effectively fighting the infection?

• A. Class switching allows the immune system to choose the most effective antibody class for fighting the infection.
• B. Different antibody classes have different strengths and functions.
• C. Certain antibody classes will not bind or recognize specific antigens/pathogens.
• D. A and B.
• E. B and C.
• F. A and C.
• G. All of the above.

Antibody class switching rearranges the genes within a B cell which controls the type of antibody secreted by the plasma B cell. During this gene rearrangement, the ______ region of the antibody is affected and the ______ region of the antibody is unaffected. This means that antibody class switching is antigen specificity ______.

• A. Constant region; Variable region; Independent.
• B. Variable region; Constant region; Independent.
• C. Constant region; Variable region; Dependent.
• D. Variable region; Constant region; Dependent.