Classes of Antibodies: Study with Video Lessons, Practice Problems & Examples

There are five classes of antibodies: IgG, IgA, IgM, IgE, and IgD, distinguished by their unique heavy chains. IgG is the most abundant, providing immunity to fetuses and newborns. IgA protects mucous membranes and is found in secretions like saliva and breast milk. IgM is the first antibody produced during infection, effective in blood. IgE is crucial for allergic responses and parasite defense, while IgD aids in B cell activation. Understanding these classes is essential for grasping humoral immunity and immune responses.

Classes of Antibodies

In this video, we're going to talk about the different antibody classes and so it turns out that there's actually 5 different classes of antibodies or, in other words, 5 different classes of immunoglobulins. And so these five classes are based on differences in their heavy chains as we'll see down below in our table. And so the 5 classes of antibodies are IgG, IgA, IgM, IgE, and IgD. And if you look at these red letters here, notice that it spells GAMED, and so notice down below right here we have this antibody stick figure playing some video games, and based on his facial expression, I'd say he's pretty gamed out from playing video games for 72 hours straight. And so hopefully, this antibody stick figure along with GAMED will help you guys remember the 5 different classes of antibodies. And so looking at this table right here, what I want you guys to notice is that the light chain for all 5 classes of antibodies is exactly the same. So the light chain λ, there'd be the one that's the Greek letter lambda. And so the light chain is not going to distinguish one antibody class from another. However, looking at the heavy chain, notice that each class of antibody has a unique heavy chain. And so it's the heavy chain that's going to distinguish one antibody from one antibody class from another. And so this first row of antibody, this first class of antibody is IgG and this is really the one that we've been talking about all along and so you can see the Y-shaped structure here that we talked about. Now, notice that IgE and IgD have very similar type of structures to IgG. However, IgA forms a dimer of these 2 Y-shaped structures and IgM tends to form a pentamer, containing 5 different Y-shaped structures here. Now, over here in this column, what we have is the primary feature of each of these antibodies. Now, IgG is actually the most prevalent and the most abundant antibody in our blood. So this is going to be one that's involved, in protecting pretty much against all types of infections including bacterial and viral infections. Now, IgA is actually going to be highly concentrated in mucous membranes and it's going to be one that is, typically secreted by our cells and, it's also prevalent in our saliva. Now, IgM interestingly enough is usually going to be the first antibody, that's going to be produced upon infection. So, IgM is going to be the one that's going to initiate the primary immune response. So the very first immune response. And then, the common second immune response would be IgG since it's so prevalent in our blood. Now IgE on the other hand here is gonna be one that's gonna defend against allergies or allergens. And so you can see here we have a guy who's saying I'm allergic to this kitty cat right here, and that's unfortunate because this is a cute little kitty cat. But IgE again is going to help defend against these allergens. Now IgD is one where its function is not really very well characterized. However, there are some, textbooks and studies that say they're involved with activating B cells and, allowing B cells to, participate in immune responses. Now over here on the far right, what we have is the distribution of these antibody classes throughout our bodies. And so notice that pretty much all of the antibodies are gonna be found in our bloodstreams, except for IgA, which again is gonna be highly concentrated in our mucous membrane. So it's gonna be lining our, digestive systems a lot. And so this here concludes our introduction to the antibody classes and we'll be able to talk more about antibodies as we move along in our course. So, I'll see you guys in our next video.

Which of the following is NOT an immunoglobin class?

• A. IgM.
• B. IgH.
• C. IgG.
• D. IgE.
• E. IgD.

IgG

In this video, we're going to talk more about the details concerning the IgG class of antibodies. The IgG antibody is considered the standard antibody in our system. This is because the IgG antibodies are the most abundant antibody class in our blood and tissues. In some individuals, IgG antibodies can make up to 80% of all immunoglobulins.

These IgG antibodies have a variety of functions. They are capable of binding to very specific antigens and can eliminate pathogens by activating the complement system's classical pathway, which, recall, we covered when we discussed innate immunity in our previous lesson videos. IgG antibodies are also known for providing immunity to a developing fetus during pregnancy, as well as to a newborn child after birth. This is due to their remarkable ability to cross the placenta between a mother and her baby, allowing the mother's IgG antibodies to protect the baby. Essentially, the mother is protecting the baby with her antibodies.

IgG antibodies are also known for having a long half-life, meaning they are very stable and can last a long time within our bodies before being broken down. This long half-life extends the duration of protection for a newborn through the first few months after birth until the baby is capable of generating its own antibodies. Essentially, a mother's antibodies protect the baby while it is a developing fetus, and for the first few months of the baby's life, until it can produce its own antibodies.

Looking at our image below, you will see it highlights the important features of the IgG class of antibodies. It showcases the standard antibody structure we discussed in previous lesson videos, and emphasizes that IgG is the most abundant class of antibodies, making up about 80%. It also highlights the role of IgG in providing infant immunity during and after pregnancy because of its ability to cross the placenta. Finally, this IgG antibody has various immune functions, including the ability to activate the complement system via the classical pathway, where it can bind to antigens. This activation leads to different types of complement system activities such as inflammation, opsonization, and cell lysis of microbes.

If you do not remember the details about the complement system classical pathway, I encourage you to review our older lesson videos on that topic. But for now, this concludes our brief lesson on the IgG class of antibodies. As we move forward in our course, we will also discuss some of the other classes of antibodies. I'll see you all in our next video.

IgA

In this video, we're going to briefly discuss the IgA class of antibody. And so the IgA class of antibody is going to help protect mucus membranes throughout our bodies. And they can also be found in body secretions such as, for example, saliva, tears, and breast milk. Now the IgA antibody is commonly found as a dimer, which means that it consists of 2 identical subunits that are held together. And this dimer is referred to as secretory IgA or sIgA for short. And within this secretory IgA molecule, which is a dimer, it consists of 2 monomers that are held together by a peptide, and we'll be able to see that down below in our image. Now the secretory IgA antibody in breast milk helps protect the intestinal tract of breastfed newborns which is why breastfeeding can actually be very healthy for newborn babies to provide them with those IgA antibodies that can help protect, again, the intestinal tract of those newborns. And so if we take a look at our image down below, we're just emphasizing those same important details of the IgA antibody. And, again, the IgA antibody is commonly found as a dimer that we refer to as secretory IgA. And so what you can see here is that there is a dimer. There's this unit right here and then there's this other identical unit right here. And these two units are held together by this blue peptide that is swirling around it. And so, that is the secretory IgA antibody. Again, this is really going to be important for protecting mucus membranes, throughout our bodies and also it's going to be found in mucus, saliva, tears, and breast milk. And so you can see those images down below. And again because it is found in breast milk, it will help protect the intestinal tract of newborn babies that are breastfed. And so, you can see the IgA antibody here dissolved within this breast milk. And so, this here concludes our brief lesson on the IgA class of antibody, And again we'll be able to get some practice applying these concepts and talk about the other classes of antibodies briefly as we move forward. So I'll see you all in our next video.

IgM

In this video, we're going to briefly discuss the IgM class of antibody. The IgM antibody is very important for controlling infections in the blood. It is actually the very first antibody that is initially produced in a primary infection by plasma cells before a process known as class switching takes place. Later in our course, in a different video, we'll talk more about this antibody class switching. The IgM class of antibody is also the largest class of antibody in terms of its size and molecular mass because IgM antibodies consist of a pentamer, which means that it is composed of 5 identical Y-shaped subunits. Because it has 5 Y-shaped subunits, each subunit with 2 antigen binding sites, that means that there are 10 antigen binding sites. Because there are so many antigen binding sites on these IgM antibodies, that makes them very effective at linking antigens together. The large size of the IgM antibody class actually prevents the IgM antibody from leaving the blood into the tissues. That's why the IgM antibody's primary role is to help control infections in the blood. Also, the IgM class of antibody is the most efficient antibody class at activating the complement system via the classical pathway.

If we take a look at our image down below, once again, we'll have an image that helps to emphasize those same features of the IgM class of antibody. Notice first that it is indeed a pentamer that consists of these five identical Y-shaped subunits. That makes it the largest antibody class. Also, it is the very first antibody that is initially created by all plasma cells prior to the antibody class switching process that we'll get to talk about in more detail later in our course. The primary role of the IgM antibody, because of its large size, is to control infections in the bloodstream. It is also the most effective antibody at activating the complement system. It activates the complement system when it binds to the antigen. Here, we have a little image that shows you C3 convertase being generated upon activation of the complement system and then all of these actions that result from the complement system activation, including inflammation, opsonization, and cell lysis of microbes. If you don't remember much about the complement system, make sure to go back to our older lesson videos to check those out. This concludes our brief lesson on the IgM class of antibody, and we'll be able to get some practice applying these concepts and talk about the other classes as we move forward. So, I'll see you all in our next video.

IgE

In this video, we're going to talk briefly about the IgE class of antibodies. The IgE antibodies are found on the surface of both basophils and mast cells. Recall that basophils and mast cells have a lot of similarities, but basophils circulate through the bloodstream, whereas mast cells are more localized within specific tissues.

When these IgE antibodies are on the surface of basophils and mast cells, they are capable of detecting and responding to very specific antigens. These IgE antibodies can actually cause the cell to undergo a process called degranulation, which you might recall from some of our previous lesson videos just means that it will cause these cells to release their granules and the contents of their granules into the environment. This can include releasing inflammatory mediators that lead to inflammation in response to some kind of infection.

Now, these IgE antibodies are very important for eliminating parasites, such as worms, and they also play an important role in the response to many different types of allergic reactions or hypersensitivities, which we'll get to talk more about later in our course in a separate video. For now, if we take a look at our image down below, we can get a more solid understanding of this IgE class of antibodies. Notice here it has the same antibody structure and again it’s found on the surface of both basophils, as well as mast cells. You can see the basophil over here, the mast cells over here, and upon binding their antigen, they cause degranulation, the release of the contents of the cytoplasmic granules. These IgE antibodies are important for protecting against parasitic infections like those caused by parasitic worms, as well as again responding to allergies or generating those allergic reactions. And again, we'll get to talk more about allergies later in our course.

But for now, this here concludes our brief lesson on the IgE class of antibody, and we'll be able to get some practice applying these concepts and then talk about the very last class of antibody. So, I'll see you all in our next video.

IgD

In this video, we're going to talk very briefly about the IgD class of antibody. IgD antibodies are found on the surface of B cells, and they signal B cell activation and maturation into an antibody-secreting plasma cell. These IgD antibodies are important for the development and maturation of the antibody response. If we take a look at our image down below, we can see here that the IgD antibody is, again, a monomer that makes up a very small percentage of all the antibodies, about 1% of all the antibodies. It can be found on the surface of B cells, as you see here. Their role on the surface of B cells is to help the B cell differentiate into plasma cells that can secrete antibodies. The IgD antibody is going to help activate the B cell and help it differentiate into a plasma cell. Ultimately, the plasma cell will be able to secrete a variety of different types of antibodies. This here concludes our brief lesson on the IgD antibody and its role in the development and maturation of the antibody response, and we'll be able to get some practice applying this as we move forward. So I'll see you all in our next video.

______ is the first immunoglobulin class produced during a primary response.

• A. IgA.
• B. IgE.
• C. IgM.
• D. IgG.

Which antibody class crosses the placenta from mother to child?

• A. IgA.
• B. IgE.
• C. IgM.
• D. IgG.

_______ is the immunoglobulin class that neutralizes viruses in the intestinal tract.

• A. IgG.
• B. IgA.
• C. IgD.
• D. IgE.

Which of the following antibodies is involved in causing basophils to release histamine when the antibody encounters an allergen?

• A. IgG.
• B. IgA.
• C. IgD.
• D. IgE.

The primary B-cell receptor is:

• A. IgD.
• B. IgA.
• C. IgE.
• D. IgG.

Review Table of Immunoglobin Classes

In this video, we're going to do a quick review of all the immunoglobulin classes or all the classes of antibodies. And so we're going to do that by completing this review table of the immunoglobulin classes. And so, what you'll notice is that we have these five classes of antibodies arranged so that they fit our mnemonic, which is GAMED, and the IgG antibody is the very first one on this list. Notice that it is a monomer and it is the standard antibody. It has a very, very long half-life which means that it's very stable and will last a long time within our bodies before it's broken down. It is the most abundant class of antibody. Around 80% of all antibodies will be IgG. It has this amazing ability to cross the placenta between the mother and the baby which is going to help provide the fetus immunity during pregnancy as well as even after birth because again, these IgG antibodies last such a long time that the mother's IgG antibodies in the baby will also help protect the baby even after birth. They're also important for activating the complement system which can lead to a variety of immune responses.

Now the IgA antibody, notice it is a dimer and a lot of times we refer to this dimer as the secretory IgA antibody or sIgA antibody. Notice that its half-life is medium and it's going to be important for protecting the mucous membranes. It's also found in many different types of body secretions including breast milk which can help protect the infant's intestinal system when a mother breastfeeds her baby.

The next antibody that we have on here is the IgM antibody which is the largest class of antibodies. It is a pentamer and its half-life is medium and it is the very first antibody that is initially created by all plasma cells prior to antibody class switching. It helps to control infections in the bloodstream. That is its main role and it also is the most effective class at activating

The IgE antibody has a very very short half-life, and so it is going to be found on both the surfaces of basophils as well as mast cells and they're important for triggering the release of inflammatory mediators causing these basophils and mast cells to degranulate, releasing their granules into their environment. The inflammatory mediators can cause inflammation and the IgE antibodies also play a role in allergic reactions, and we'll get to talk more about that later in our course when we focus our attention on allergic reactions and hypersensitivities. They also play an important role in protecting against parasitic infections as well, like parasitic worms for example.

Now last but not least, we have the IgD antibody which is again a monomer and has a short half-life, which means that it does not last very long within the body. Now the IgD antibodies are going to be found on the surface of B cells or can be found on the surface of B cells and they play an important role in helping to trigger B cell activation and differentiation into antibody-secreting plasma cells.

And so this here concludes our brief review of the 5 classes of antibodies, and we'll be able to get some more practice applying these concepts as we move forward. So I'll see you all in our next video.

Each class of antibody is specifically defined by its

• A. Amino acid sequence of the variable region of the light chain.
• B. Amino acid sequence of the constant region of the heavy chain.
• C. Ability to cross the placenta.
• D. Disulfide bonds.

Match the following antibody classes with their description:

a)   IgA.      b)  IgG.         c)  IgE.         d)  IgM.      e)  IgD.

___ First antibody produced during primary response.

___ Protects mucous membranes.

___ Most abundant antibody.

___ Found on the surface of B cells.

___ Triggers allergic reactions to allergens.

Okay, everyone. Here we have a great review question about the different classes of antibodies because we are going to match the antibody class with one of their descriptors. So we have our 5 different classes, and we know that these different antibodies do a variety of things, but let's try to figure out which one does each of these descriptions. So the first one is the first antibody produced during a primary response. So in primary response is when your body is infected by a new pathogen that it has never seen before. And this is going to be the first antibody that is produced. This is going to be IgM. It is going to be the initial antibody produced by plasma cells before that plasma cell changes to a different class of antibodies. We call this class switching, and you will learn about this soon. But IgM is going to be produced first by all the plasma cells until they're told to switch to a different class. So that means that it is the 1st antibody produced. So that means we're going to put d for our first answer. Okay. So now we have protects the mucus membranes. Remember that this is going to be the antibody that is found in breast milk. And whenever babies breastfeed, it is going to protect them from pathogens that they may ingest because when they're first born, they have a weak immune system. So this antibody protects the mucus membranes in the digestive tract. And remember, this is IgA. So the correct answer to this one is gonna be a. Alright. So now we have 3 left. The third one says the most abundant antibody. You might be thinking this is IgM because it's the first one to be made, but it's actually not. The most abundant antibody makes up about 80 percent of the antibodies in our body, and it's the only one that crosses the placenta between mother and baby and protects the infant for the first couple months of its life. And that is IgG. So the correct answer here is b. Okay. We have 2 left. The 4th one says found on the surface of B cells. It is the most common type of B cell receptor, and this antibody is involved in the differentiation and activation of B cells. This is going to be IgD. So that means answer choice e is the next answer. Excuse me. Now we have the last one, triggers allergic reactions to allergens. This antibody is going to activate mast cells and basophils, causing them to release histamine and trigger an inflammatory response, which is also known as an allergic reaction. And that is IgE, the only answer left. There we go. So that is going to be all of the different antibody classes and their major or most famous description or scenario that they perform. Okay, everyone. Let's move on to our next video.

Here’s what students ask on this topic:

What are the five classes of antibodies and their primary functions?

The five classes of antibodies are IgG, IgA, IgM, IgE, and IgD. IgG is the most abundant and provides immunity to fetuses and newborns by crossing the placenta. IgA protects mucous membranes and is found in secretions like saliva and breast milk. IgM is the first antibody produced during an infection and is effective in the blood. IgE is crucial for allergic responses and defense against parasites. IgD aids in B cell activation and maturation. Each class has unique roles in the immune response, making them essential for humoral immunity.

How does IgG provide immunity to fetuses and newborns?

IgG provides immunity to fetuses and newborns by crossing the placenta from the mother to the baby. This transfer of IgG antibodies helps protect the developing fetus during pregnancy. After birth, the IgG antibodies continue to provide immunity to the newborn for the first few months of life until the baby can produce its own antibodies. This is possible because IgG has a long half-life, allowing it to remain stable and effective in the baby's body for an extended period.

What is the role of IgA in the immune system?

IgA plays a crucial role in protecting mucous membranes throughout the body. It is commonly found in body secretions such as saliva, tears, and breast milk. In breast milk, IgA helps protect the intestinal tract of breastfed newborns. IgA is often found as a dimer, known as secretory IgA (sIgA), which consists of two identical subunits held together by a peptide. This structure allows IgA to effectively guard mucosal surfaces against pathogens.

Why is IgM considered the first antibody produced during an infection?

IgM is considered the first antibody produced during an infection because it is the initial antibody synthesized by plasma cells in response to a primary infection. IgM is a pentamer, consisting of five identical Y-shaped subunits, making it the largest antibody class. Its large size and multiple antigen-binding sites (10 in total) make it highly effective at linking antigens together and controlling infections in the bloodstream. IgM also efficiently activates the complement system via the classical pathway.

What is the significance of IgE in allergic reactions?

IgE is significant in allergic reactions because it binds to the surface of basophils and mast cells, which are involved in the immune response. When IgE antibodies on these cells encounter specific antigens, they trigger degranulation, releasing inflammatory mediators that cause inflammation. This process is crucial for defending against parasitic infections, such as worms, and plays a key role in allergic reactions and hypersensitivities. IgE-mediated responses can lead to symptoms like itching, swelling, and anaphylaxis in severe cases.