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.
Antibody Class Switching: Videos & Practice Problems
Antibody class switching is a crucial process where activated B cells change the class of antibodies they produce, initially starting with IgM and potentially switching to IgG, IgA, or IgE. This genetic rearrangement occurs in the DNA of B cells, specifically altering the constant region while preserving the variable region, ensuring specificity for the same antigen. The process involves the deletion of certain gene segments, allowing the expression of the new antibody class. Understanding this mechanism is vital for grasping adaptive immunity and the body's response to pathogens.
Antibody Class Switching
Video transcript
Class switching occurs when which of the following scenarios occur?
Which lymphocyte is responsible for inducing class switching in B cells?
Why is class switching of antibodies during an infection important for effectively fighting the infection?
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 ______.
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More setsHere’s what students ask on this topic:
What is antibody class switching and why is it important?
Antibody class switching is a process where activated B cells change the class of antibodies they produce. Initially, B cells produce IgM antibodies, but through genetic rearrangement, they can switch to producing other classes like IgG, IgA, or IgE. This rearrangement occurs in the DNA of B cells, specifically altering the constant region while preserving the variable region, ensuring the antibody maintains specificity for the same antigen. This process is crucial for adaptive immunity as it allows the immune system to produce antibodies that are more effective in different physiological contexts, enhancing the body's ability to respond to pathogens.
Created using AIHow does the genetic rearrangement occur during antibody class switching?
During antibody class switching, genetic rearrangement occurs in the DNA of activated B cells. This involves changes in the constant region of the antibody gene. Specific DNA segments coding for the constant region are deleted, allowing the expression of a new antibody class. For example, if the segments for IgM and IgD are deleted, the remaining segments might code for IgG, IgA, or IgE. The variable region, which determines antigen specificity, remains unchanged. This ensures that the new antibody class still targets the same antigen but can perform different functions in the immune response.
Created using AIWhat role does the constant region play in antibody class switching?
The constant region of an antibody determines its class and effector functions, such as binding to different receptors on immune cells or activating complement pathways. During antibody class switching, the constant region undergoes genetic rearrangement, where specific DNA segments are deleted. This allows the B cell to produce a different class of antibody (e.g., switching from IgM to IgG) while maintaining the same antigen specificity due to the unchanged variable region. The new constant region endows the antibody with different functional properties, enhancing the immune response's versatility.
Created using AIWhy does the variable region remain unchanged during antibody class switching?
The variable region of an antibody remains unchanged during class switching to ensure that the antibody retains its specificity for the same antigen. The variable region is responsible for binding to the antigen's epitope, and any changes to this region could alter the antibody's ability to recognize and bind to the antigen. By preserving the variable region, the immune system ensures that the new class of antibody (e.g., IgG, IgA, or IgE) produced after class switching can still target the same pathogen effectively, while the constant region changes to provide different effector functions.
Created using AIWhat triggers antibody class switching in B cells?
Antibody class switching in B cells is triggered by signals from helper T cells and cytokines. When a B cell is activated by an antigen, helper T cells provide additional signals through direct cell-to-cell contact and the release of cytokines. These signals induce the genetic rearrangement necessary for class switching. Different cytokines can influence the specific class of antibody that the B cell will switch to, allowing the immune system to tailor its response to different types of pathogens. For example, IL-4 can promote switching to IgE, while IFN-γ can promote switching to IgG.
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