Antibody Class Switching: Study with Video Lessons, Practice Problems & Examples

Antibody class switching is a process where activated B cells change the class of antibody they produce, initially starting with IgM. This occurs through genetic rearrangement of the DNA encoding the antibody's constant region, allowing the plasma cells to switch to classes like IgG while maintaining specificity for the same antigen. The variable region remains unchanged, ensuring the antibody binds to the same epitope. This process is crucial for effective humoral immunity, enabling a more tailored immune response as the body encounters different pathogens.

Antibody Class Switching

In this video, we're going to begin our lesson on a process known as antibody class switching. 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. 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. 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. 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. 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. Antibody class switching, once again, occurs via changes in the DNA. It occurs more specifically via genetic rearrangement of the DNA encoding the antibody's constant region. Recall that we discussed the constant region of antibodies when we discussed the structure of the antibody. It's important to note that, even after antibody class switching, when plasma cells go from secreting IgM to IgG, the new antibody class still maintains the specificity for the same exact epitope of the same exact antigen. This is because the variable region of the antibody is unchanged. 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. 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. It's really the gene segments that remain for the constant region that are first in line that are going to be expressed. If we take a look at our image down below, we can get a much better understanding of this process of antibody class switching. 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. Sometimes when these activated B cells divide, there is no loss of their DNA segments. In those cases, these activated B cells, when they divide, there's going to be no changes to their DNA. When there are no changes to the DNA, what that means is there's no changes to the constant regions. Notice that here we have the 5 different classes of antibodies. 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. By first in line, we mean here furthest to the left in this image. It's the IgM class that is actually going to be programmed to be first in line. What this means is that it is the IgM class of antibody that is going to be produced initially. 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. 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. 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. 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. 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. When that happens, when IgM and IgD are deleted and removed, the only segments that remain are IgG, IgE, and IgA. You can see those that are remaining down below right here. What you'll notice is that again, it's the gene segment that is first in line that is going to be expressed. In this case, IgG is the first gene segment, furthest to the left. That means that IgG is the class of antibody that is going to be secreted and produced by this plasma cell. Here you can see a plasma cell that is secreting the IgG class of antibody. 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 secreting. 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. 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. We'll be able to get some practice applying these concepts as we move forward in our course. 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.

Here’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 antibody they produce, initially starting with IgM. This occurs through genetic rearrangement of the DNA encoding the antibody's constant region, allowing the plasma cells to switch to other classes like IgG, IgA, or IgE. The variable region remains unchanged, ensuring the antibody binds to the same epitope of the antigen. This process is crucial for effective humoral immunity, enabling a more tailored immune response as the body encounters different pathogens. By switching antibody classes, the immune system can better adapt to and neutralize various threats, enhancing overall immune protection.

How does the DNA rearrangement occur during antibody class switching?

During antibody class switching, DNA rearrangement occurs specifically in the constant region of the antibody gene. Initially, B cells produce IgM antibodies. When class switching is triggered, specific DNA segments coding for the constant regions of other antibody classes (e.g., IgG, IgA, IgE) are brought into proximity by looping out and deleting intervening DNA segments. This rearrangement allows the B cell to express a different constant region while maintaining the same variable region, ensuring the antibody's specificity for the antigen remains unchanged. The new antibody class produced can then perform different functions in the immune response.

What role do cytokines play in antibody class switching?

Cytokines play a crucial role in directing antibody class switching by influencing which antibody class a B cell will switch to. Different cytokines promote switching to different antibody classes. For example, Interleukin-4 (IL-4) promotes switching to IgE, while Interferon-gamma (IFN-γ) promotes switching to IgG. These cytokines are secreted by helper T cells and other immune cells in response to specific pathogens or immune challenges. By guiding the class switching process, cytokines help tailor the immune response to be more effective against the particular type of pathogen encountered.

Can antibody class switching affect the antigen-binding specificity of the antibody?

No, antibody class switching does not affect the antigen-binding specificity of the antibody. The process involves changes in the constant region of the antibody's DNA, but the variable region, which determines the specificity for the antigen, remains unchanged. This means that even after switching from IgM to another class like IgG, the antibody will still bind to the same epitope on the same antigen. This allows the immune system to maintain its ability to recognize and target the specific pathogen while adapting the antibody's effector functions to better combat the infection.

What are the different classes of antibodies that B cells can switch to?

B cells can switch to several different classes of antibodies, each with distinct functions. The main classes include:

• IgM: The first antibody produced in response to an infection, effective in forming antigen-antibody complexes.
• IgG: The most abundant antibody in blood and extracellular fluid, providing long-term immunity and capable of crossing the placenta.
• IgA: Found in mucosal areas, such as the gut, respiratory tract, and urogenital tract, as well as in secretions like saliva and breast milk.
• IgE: Involved in allergic reactions and protection against parasitic infections.
• IgD: Functions mainly as a receptor on B cells that have not been exposed to antigens.

Class switching allows the immune system to adapt and use the most effective antibody class for different types of infections and immune challenges.