Introduction to B Lymphocytes - Video Tutorials & Practice Problems
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1
concept
Humoral Immunity
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3m
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In this video, we're going to begin our introduction to B lymphocytes or B cells. And so first, we need to recall from some of our previous lesson videos that B lymphocytes or B cells play an important role in adaptive humoral immunity. And recall that humoral immunity is the part of the adaptive immune system that is going to be targeting and destroying extracellular pathogens or pathogens that are on the outside of host cells. And these uh this humoral immunity will be able to destroy these extracellular pathogens by using B cells um as well as using what are known as antibodies. And we'll get to talk a lot more about antibodies as we move forward in our course. Now also recall from some of our previous lesson videos that the dendritic cells which are antigen presenting cells or uh an A PC, they have both MH C class one and MH C class two molecules. And so that means that they're capable of activating T cells. Uh uh both types of T cells, the cytotoxic and the helper T cell. And when they activate the helper T cell, the helper T cell will then go on to be able to activate the B cell and then the B cell will be able to carry out its immune functions. And so if we take a look at our image down below, you'll notice it's an image that we've seen before in our previous lesson videos. And so once again, we have our primary lymphoid organs at the top which include the thymus and the bone marrow. The thymus is where the T cells fully develop and the bone marrow is where the B cells fully develop. Now notice that because we've briefly discussed the T cells already that the T cell area over here is pretty much all gray out because we've already talked about it briefly in our previous lesson videos. And here in this video, we're gonna be focusing on the B cells. And so these fully mature naive B cells will migrate from the primary lymphoid organs to the secondary lymphoid organs. And so here we have a naive or inactive B cell. Now, this naive B cell has not yet encountered an antigen, but when it does encounter its antigen, it will be able to internalize that antigen process that antigen and then display that antigen on its MH C class two molecules. And so when it's displaying those MH C class two molecules, uh those antigens on those Mh C class two molecules, the effector helper T cell can recognize those antigens on the MH C class two. And so the effector helper T cell can then cytokines that can ultimately activate the B cell and the activated B cell. As we've discussed before. In some of our previous lesson, videos are gonna be able to proliferate or divide to create clones as well as differentiate into either uh memory B cells as you see here. And the memory B cells will be important for a secondary infection. Uh or the activated B cells could differentiate into what are known as plasma cells. And plasma cells are really the effector uh B cell. And so these plasma cells are going to be able to release and secrete antibodies and these antibodies can carry out many different types of immune functions. And so as we move forward in our course, we're gonna talk a lot more details about this activation process of the B cells, uh the differentiation of the memory and the plasma cells and then also the antibodies that these plasma cells can produce. And so this year concludes our brief introduction to these B lymphocytes or B cells. And again, we'll be able to learn more as we move forward. So I'll see you all in our next video.
2
Problem
Problem
Match the correct form of adaptive immunity to the scenarios below.
A. Cell-Mediated Immunity. B. Humoral Immunity
_____ 1. A macrophage acting as an APC is activated by a CD4 effector cell.
_____ 2. A naive B cell is activated after binding an antigen and differentiates into a plasma cell.
_____ 3. Responds to exogenous antigens.
_____ 4. Responds to endogenous antigens.
_____ 5. A liver cell infected with a virus undergoes apoptosis when signaled by a CD8 effector cell.
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2m
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3
concept
B Cell Receptors
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4m
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In this video, we're going to briefly discuss B cell receptors. And so first, we need to recall from some of our previous lesson videos that B cells develop in the bone marrow. And these B cells have thousands of identical B cell receptors embedded in their membranes. And these B cells are also associated with what are known as antibodies. And that's because these B cells have the ability to differentiate into what are known as plasma cells that secrete many antibodies. And we'll get to talk a lot more about plasma cells and antibodies as we move forward in our course. But going back to these B cell receptors, these B cell receptors are commonly abbreviated as BC RS. And again, each B cell is going to have thousands of identical BC RS embedded in their membrane. Now, these B cell receptors or BC RS, these are receptors that allow B cells to recognize and attack extracellular pathogens. Now, one of the main differences between B cell receptors or BC RS and T cell receptors or TCRS is that recall that TCRS, they do not bind to free antigens. TCRS can only bind to presented antigens on MH CS. Now, B cell receptors, they actually can bind to free floating antigens. And so the free floating antigens are able to bind to the BC RS. And when those free floating antigens bind to the BC RS, they can then be internalized and processed. And then those free floating antigens can be presented by the cell for activation by helper T cells. And they will be presenting those free floating antigens on their MH C class two molecules. Now, some important things to note about these BC Rs is that BC RS are practically membrane embedded antibodies. And so the structures of antibodies are going to resemble the structure of BC RS and vice versa. And so they have very, very similar overall structure and we'll get to talk about the structure of BC RS and antibodies in more detail as we move forward in our course. Now, another important thing to note is that the BC RS of A B cell are pretty much almost identical uh two, the antibodies that that B cell eventually secretes. And so uh that's another important thing to keep in mind. And so if we take a look at our image down below, uh we can get a better understanding of these B cell receptors. And so notice on the left hand side over here, we're showing you A B cell and this B cell can have again, thousands of identical BC RS embedded in their membrane. And these are the B cell receptors. Now notice that these BC RS, they take on a shape that resembles that of the antibodies uh that they eventually produce. And again, the BC RS, they are capable of binding to free antigens or antigens that are not being presented. And so this is a free antigen. And again, it's not, uh it's not being presented. Now, if we zoom into this BC R over here, which you'll notice is that again, the BC R is gonna have this Y shaped structure that you see right here. This is our B cell receptor. And uh uh what you see here is that this little yellow region here represents the antigen binding site of the B cell receptor. So this is what is, this is the region of the BC R that binds the antigen and notice that there are two antigen binding sites allowing for the BC R to bind to two antigens at once. And so notice over here, we are showing you a free antigen and uh notice that it's binding to this specific epitope of the free antigen. And so that's a term that we talked about in some of our previous lesson videos. And so uh this year concludes our brief introduction to B cell receptors and BC RS and their ability to bind to free antigens. And we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video.
4
Problem
Problem
What is the difference between a TCR and a BCR?
A
TCRs must be presented an antigen on an MHC molecule from an APC.
B
BCRs must be presented an antigen on an MHC molecule from an APC.
C
TCRs mimic the structure of antibodies and are essentially the same.
D
BCRs are composed of amino acid chains & TCRs are composed of various carbohydrates.
E
TCRs are composed of amino acid chains & BCRs are composed of various carbohydrates.
5
Problem
Problem
A naive B cell is activated when:
A
The B cell’s BCR binds to an endogenous antigen presented by an APC.
B
The B cell is told to differentiate into a plasma cell or memory B cell by a CD4 effector cell.
C
The B cell’s BCR binds to a “free” antigen that is not bound to an APC.
D
When A and B occur.
E
When B and C occur.
6
concept
Naive B cells Become Effector (Plasma) Cells & Memory Cells
Video duration:
4m
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In this video, we're going to continue our introduction to B lymphocytes by talking about the ability for naive B cells to become effector plasma cells and memory B cells. And so first, what we need to know is that before A B cell encounters a free antigen that B cell exists in an inactive form that we refer to as a naive B cell. And so once again, a naive B cell is really just an inactive B cell that has not yet encountered its free antigen. Now upon encountering its free antigen and then presenting that free antigen on an MH C class two molecule, the naive B cells are going to be bound and activated by helper T cells. And again, recall from our previous lesson, videos that helper T cells can help to activate B cells. Now these activated B cells are capable of proliferating or multiplying to create identical clones of itself as well as differentiating or changing its phenotype to become either an effector plasma cell or a memory B cell. And so the effector plasma B cells are going to be short lived cells that make antibodies and they can make thousands of antibodies per second. So they're making lots and lots of antibodies and these antibodies as we'll learn, moving forward in our course, are capable of immediately responding to the first infection. And so they are able to respond to the infection in many different ways. Now, the memory b cells, on the other hand, these are long lived cells and they do not respond immediately to the first infection. Instead, these memory b cells that are long lived cells, they somewhat remember the antigen and they're capable of making antibodies even faster in future infections. And so really, they're only going to help with a future infection and help eliminate that future infection even faster than the primary infection uh was eliminated. And so if we take a look at our image down below, we can get a better understanding of the ability for the naive B cell to differentiate into either an effect or plasma cell or a memory B cell. And so notice over here on the left hand side, what we have is a naive B cell, an inactive B cell. And when this naive B cell encounters a free antigen, as you see right here, a free floating antigen that's not being presented. This free antigen can be internalized into the B cell processed and then uh presented on MH C class two molecules and the MH C class two molecules uh are going to allow helper T cells to activate the naive B cell. And activation of the naive B cell will allow the naive B cell to differentiate either into a memory B cell as we see right here. Or it would allow the B cell to differentiate into a plasma cell. And the plasma cell would be the effector cell again, capable of releasing and producing thousands of antibodies per second, releasing those antibodies into the environment. And those antibodies that are released into the environment can then carry out several different immune responses. Which again, we'll get to talk about as we move forward in our course. Now again, recall that on these B cells, they have these B cell receptors or BC RS and the BC RS that A B cell has are pretty much membrane embedded versions of the antibodies that that B cell ends up producing after it differentiates into a plasma cell. And so uh this year concludes our brief lesson on how naive B cells can become effector plasma cells and memory cells. And once again, we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video.
7
Problem
Problem
Antibodies are made by:
A
Red blood cells.
B
Plasma cells.
C
Dendritic cells.
D
Helper T cells.
8
Problem
Problem
In which of the following sites in the body can B cells be found?
A
Lymph nodes.
B
Spleen.
C
Red bone marrow.
D
Intestinal wall.
E
All of the above.
9
Problem
Problem
The antibody-secreting progeny of an activated B cell are called:
A
Antibodies.
B
Sensitized T cells.
C
Activated macrophages.
D
Plasma cells.
10
Problem
Problem
Which of the following are properties of B cells?
A
Naive B cells, like naive T cells, can differentiate into effector and memory B cells once activated.
B
Effector B cells when activated secrete antibodies which fight a novel infection.
C
Memory B cells when activated secrete antibodies which fight subsequent infections more effectively.
D
To become activated, a naive B cell must present an immunogenic antigen to an effector CD4 cell.
E
All are properties of B cells.
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