Introduction to T Lymphocytes - Video Tutorials & Practice Problems
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1
concept
Cell-Mediated Immunity
Video duration:
3m
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In this video, we're going to begin our introduction to T lymphocytes or T cells. And so first, we need to recall from some of our previous lesson videos that T lymphocytes or T cells play an important role in cell mediated immunity, which recall is a part of adaptive immunity. And so cell mediated immunity is going to be targeting and destroying intracellular pathogens or disease causing agents that have made their way inside of a host cell. And it does this by using once again T cells or T lymphocytes. And so down below what we're going to do is focus on this image, but we're going to continue to introduce and uh talk about T cells and T lymphocytes as we move forward. And so what you'll notice here is we're showing you the primary lymphoid organs here and recall that T cells are going to be uh developed in the thymus. And after these T cells are fully developed, the naive forms of the T cells or the inactive forms of the T cells will migrate to the secondary lymphoid organs like tonsils or lymph nodes or the spleen. And so really what we're going to learn moving forward is that there are two major types of T cells, there are cytotoxic T cells or TC cells. And then there are also helper T cells or TH cells. And as we move forward in our course, we will differentiate between these two types of T cells. Now, uh here we're showing you that both the cytotoxic T cell and the helper T cell need to be activated by an antigen presenting cell such as a dendritic cell. And so here we're showing you a dendritic cell presenting antigens on its surface so that they can activate these T cells and upon activation of the T cells, these T cells will begin to divide and differentiate into either memory T cells. Uh So notice that there are both memory cytotoxic T cells, memory TC cells, but there are also memory th cells as well or memory helper T cells. And in addition to generating these helper, uh these memory cells, uh they also will differentiate into effector cells as well, factor helper T cell and also factor cytotoxic T cell. And so uh what you'll notice is that it's these effector uh T cells that can go on to carry out uh the immune functions. And uh the memory T cells are just stored for uh generating an immune response to a secondary infection, a potential secondary infection. Uh Now notice that the B cells are being shown over here on the right hand side, but we're going to talk about the B cells later in our course, after we finish talking about the T cells. And so everything that we've discussed here uh in this video about the T cells, we're going to break down and explain in more details as we move forward. And so this year concludes our brief introduction to T lymphocytes. And again, we'll continue learning about them as we go forward. So I'll see you all in our next video.
2
Problem
Problem
Which of the following answers is a major difference between cell-mediated and humoral immunity?
A
Cell-mediated immunity utilizes T cells while humoral immunity utilizes B cells to respond to infection.
B
Cell-mediated immunity involves antigens presented on APCs while humoral immunity involves free antigens.
C
Cell-mediated immunity responds to antigens outside of cells. Humoral immunity responds to antigens within a cell.
D
A and B.
E
B and C.
F
All of the above are major differences between cell-mediated and humoral immunity.
3
concept
T-Cell Receptors
Video duration:
5m
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In this video, we're going to talk more details about T cell receptors. And so first, we need to recall from some of our previous lesson videos that T cells are immune system cells that play a huge role in adaptive cell mediated immunity. And recall that these T cells they develop in the thymus. And these T cells have thousands of identical T cell receptors that are embedded in their membranes. Now, these T cell receptors are commonly abbreviated as TCRS. And so these T cell receptors or TCRS are again receptors that allow T cells to recognize and attack very specific intracellular pathogens or pathogens that are on the inside of a host cell. Now also recall from some of our previous lesson videos that these T cell receptors are not capable of binding free antigens. These T cell receptors can only bind to presented antigens or antigens that are presented on the surface of antigen presenting cells. Now, in terms of the structure of these TCRS, each TCR consists of two polypeptide chains, an alpha chain and a beta chain. And these two polypeptide chains are linked via special types of covalent bonds known as disulfide bonds And also each of these polypeptide chains contains two different regions. The first region that each of them contains is a variable region. And the second region that each of them contains is a constant region. And we'll be able to see all of this down below in our image in a moment. Now, the variable region of each of the polypeptide chains as its name implies is a region of the polypeptide chain that varies between different TCRS and so different TCRS will have different variable regions. And also this variable region is the region that will directly bind to the presented antigen. Once again, the TCRS are only capable of binding to presented antigens. They are not capable of binding to free antigens. Now, the amino acid sequence variation that's in this variable region accounts for the many different types of antigens that different TCRS can bind. And so different TCRS are capable of binding to different antigens. But once again, a single T cell will have thousands of identical T cell receptors, which means that a single T cell is only capable of uh generating a uh an immune response towards one very specific antigen. Now, the constant region is the second region that each of these polypeptide chains contains. And the constant region as its name implies, is going to be a region that remains relatively constant uh in terms of its amino acid sequence. And also this constant region is the region that's closest to the cell surface and want to get, and once again, it is going to be very constant in its amino acid sequence. And so if we take a look at our image down below, we can get a better understanding of these T cell receptors. And so notice on the left hand side over here, we're showing you a T cell and again, recall that these T cells are going to have thousands of identical T cell receptors. And notice that here, we're showing you these T cell receptors that these uh T cells can have. And uh notice that this, if we zoom into this particular T cell receptor, uh we can see uh that is what this image is showing a zoom in of this particular T cell receptor. And when we look at the entire T cell receptor, you'll notice that it has those two polypeptide chains. It has this alpha chain over here on the left and then it has this beta chain over here on the right. And the two chains are linked via disulfide bonds. Now notice that each of these chains contains a variable region which is here at the top. And this variable region that you see right here again, is going to vary from one TCR to another TCR um vary between different TCRS. And uh also it's going to allow for the binding uh to a presented antigen. Um Now, down below uh in this green region, what we have is the constant region of these polypeptide chains and the constant region is gonna remain relatively constant from one TCR to a different TCR. And so this here concludes our brief introduction to these T cell receptors. And once again, we'll be able to get some practice applying these concepts and learn more about T lymphocytes as we move forward in our course. And so I'll see you all in our next video.
4
Problem
Problem
Which of the following is NOT a component of TCRs?
A
Alpha chain.
B
CD3 complex.
C
Beta chain.
D
Constant & Variable Regions.
E
None of the above.
5
Problem
Problem
What is the importance of the variable region of T-cell receptors?
A
The variable region is the closest region to the cell’s surface and stabilizes the receptor in the plasma membrane.
B
The variable region directly binds to antigens.
C
The variable region varies in its amino acid sequence allowing different TCRs to bind different antigens.
D
The variable region directly binds to antibodies.
E
A and B.
F
B and C.
G
C and D.
6
concept
Naive T Cells Become Effector & Memory T Cells
Video duration:
7m
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In this video, we're going to introduce naive T cells, effector T cells and memory T cells. And we'll also talk about how these naive T cells can actually become effector and memory T cells. Now, it is important to note that before a developed T cell encounters, its presented antigen, that it's supposed to generate an immune response to that T cell exists in an inactive form that we refer to as a naive T cell. And so a naive T cell is a T cell that is inactive because it has not yet encountered a presented antigen. And so before the T cell can actually generate an immune response, the naive T cell must become activated. And so when naive T cells encounter presented antigen on an antigen presenting cell, such as for example, a dendritic cell, then that naive T cell can become activated. And so activated T cells are capable of doing two things they're capable of proliferating or multiplying to create more of identical clones of itself. And they're also capable of differentiating or changing their phenotype to become a slightly different cell type. And so when they differentiate to change their phenotype, they can differentiate into either an effector T cell or they could differentiate into a memory T cell. And so the effector T cells are going to be short lived cells. And these uh affected T cells that are short lived, they generate an immediate immune response to the first infection upon encountering the antigen for the first time. Now, the memory T cells, on the other hand, these cells are long lived cells that can survive for many, many years, perhaps even the lifespan of the the human being. Now, these memory T cells that are long lived, they also remember the antigen and by remember the antigen, what that means is that they do not respond to the first infection. However, they will generate a very fast response to any future infection such as a secondary infection. And so that helps to create a stronger immune response when you are exposed to uh one of these antigens a second time. And so we'll get to talk more about uh these details here as we move forward in our course. Now, it is also important to note that there are two main types of effector T cells and two main types of memory T cells. And those are going to be the cytotoxic and helper T cells. And so that means that there are effector cytotoxic effector T cells, cytotoxic memory T cells. And there are also helper effector T cells and helper memory T cells. And so if we take a look at our image down below, we can get a better understanding of all of these T cells. And so notice on the left hand side over here, we're focusing in on the cytotoxic T cells. And remember that the cytotoxic T cells have an effector cytotoxic T cell. And there's also memory cytotoxic T cells. And so uh notice that these uh T cells originally, they start off in their naive forms. And so here we have a naive T cell and recall that the naive T cell is going to be inactive because it has not yet encountered its presented antigen. However, when the naive T cell is uh introduced to its presented antigen by an antigen presenting cell such as a dendritic cell. And so this cell over here is our antigen presenting cell presenting an antigen to this naive T cell. Uh when the naive T cell recognizes uh a presented antigen, then that can lead to T cell activation, which is what we see right here. And so this T cell activation will allow uh uh the, the T cell to proliferate divide and differentiate into either an effector cytotoxic T cell. So this would be a cytotoxic, uh an effective cytotoxic T cell being represented right here. And notice that we're showing this cytotoxic T cell somewhat like the grim reaper here because it's going to have some immune responses that are kind of similar to a grim reaper. And we'll be able to talk about that later as we move forward in our course. And so notice that the cytotoxic effector T cell is capable of generating an immune response. And later, we'll also get to talk about how these cytotoxic T cells are also referred to as CD eight cells, which is why this uh character here has a CD eight on it. Now again, in addition to differentiating into effector cytotoxic T cells, the cytotoxic, the activation of the naive cytotoxic T cell could also lead to the differentiation into a memory cytotoxic T cell, which is what we have over here. And the memory cytotoxic T cell does not respond to the very first infection. Instead, it's a long lived cell that is capable of responding faster to future infections. And so notice that this uh memory cytotoxic T cell here is saying I will remember this antigen if we uh encounter it again in the future. Now, over here, on the right hand side, we have an analogous image but instead of cytotoxic T cells, these are for helper T cells. And so again, the helper T cells also have an effector helper T cell and a memory helper T cell. And so again, it originally starts off as a naive T cell. But upon uh recognizing and being presented, its antigen by an antigen presenting cell like a dendritic cell, the naive T cell which is inactive can become activated. So we have T cell activation and again, that leads to the differentiation and the proliferation of these cells. So, uh it can differentiate into a helper T cell, which is the effector T cell and uh or it could differentiate into a memory T cell which again uh is going to generate a uh faster response and future infections. Now, the helper T cell is going to uh as its name implies, help activate other components of the immune system. And so we'll be able to talk more about the uh actual um uh immune responses of these uh T cells as we move forward in our course. But for now, this here uh has uh concluded our lesson on naive T cells and how these naive T cells can become activated to uh differentiate into either effector T cells or memory T cells. And how there are also cytotoxic and helper versions of each of these T cells. And so uh this year concludes uh this lesson 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.
7
Problem
Problem
A naive lymphocyte:
A
Has encountered an antigen with its receptor but has not yet produced antibodies.
B
Has not yet encountered an antigen recognized by its receptors but is producing antibodies.
C
Has encountered an antigen and has undergone apoptosis.
D
Has fully developed antigen receptors but has not yet encountered an antigen.
E
Has produced antibodies despite not having developed receptors.
8
Problem
Problem
Which of the following statements about effector T cells is NOT true?
A
Effector T cells are long-lived cells that allow the immune system to respond quickly to subsequent infections.
B
Effector T cells can take two forms: Cytotoxic T Cells & Helper T Cells.
C
Effector T cells trigger an immediate immune response to a novel infection.
D
Effector T cells are short-lived immune cells.
E
All of the above statements about effector T cells are true.
9
concept
Cytotoxic T Cells vs. Helper T Cells
Video duration:
5m
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In this video, we're going to further differentiate between cytotoxic T cells and helper T cells. And so we need to recall from our previous lesson videos that there are two types of effector and memory T cells that are responsible for generating an immune response to antigens. And those two main types of T cells are once again, the cytotoxic T cell and the helper T cell. Now, the cytotoxic T cell is commonly abbreviated as TC cell or CD eight cell. And the CD A is specifically referring to a uh a specific uh protein that's on the surface of these cytotoxic T cells. And so cytotoxic T cell, TC cell and CD eight cell are all referring to the same types of cell. And these cytotoxic T cells, they're mainly responsible for releasing chemicals that induce apoptosis of host cells that are infected with intracellular pathogens. And so once again, these T cells are targeting intracellular pathogens. Now, uh the helper T cell on the other hand, is going to have a different function than the cytotoxic T cell. The helper T cell is going to be commonly abbreviated as TH or CD four cells. And again, CD four is just the name of a protein that's found on the surface of these helper T cells. And uh helper T cells, th cell and CD four cell are all referring to the same type of cell. Now, once again, the helper T cells are different than cytotoxic T cells. They do not have the same functions. The helper T cell as its name implies is going to help other cells become activated. And so they are going to produce cytokines to help stimulate and activate other immune cells, for example, helping to stimulate and activate B cells. And again, we'll get to talk more about B cells later in our course, after we finish talking about the T cells. And so again, uh the cytotoxic T cell can be abbreviated as CD eight cell and the helper T cell can be abbreviated as CD four cell. And that's something that's very important for you to uh remember. And so again, CD here actually stands for cluster of differentiation. And these are specific markers uh protein markers that are on the surface of these specific types of cells. And it's one of the ways that scientists can differentiate between the two types of T cells. Uh And so, uh these CD uh markers are clusters of surface proteins on T cells that again can be used to differentiate cytotoxic T cells and helper T cells. Uh So again, the CD markers, uh the cytotoxic T cells are CD eight and the helper T cells are CD four. And it's the CD markers that can actually dictate or help to dictate the interactions and the functions of the cytotoxic and helper T cells. And so if we take a look at our image down below, we can further differentiate between the cytotoxic and the helper T cell. And so on the left hand side of our image, what we're showing you is the cytotoxic T cell. And what you'll notice is that our cytotoxic T cell uh has these CD eight markers on its surface. And again, uh these CD eight markers are uh going to allow for scientists to um basically differentiate the cytotoxic T cell from the helper T cell which we have on the right now, the cytotoxic T cell we're showing here also um as the grim reaper here because what it does is it can induce apoptosis and host cells that have been affected by an intracellular pathogen. So, for example, over here, we have another host cell that is infected and it is infected with a virus as you can see right here. And so, because this host cell is infected, this cytotoxic T cell can come and it can induce apoptosis of this infected host cell. And that ultimately helps to protect um the entire human body and uh defend ourselves against these in intercellular pathogens. Uh Now again, we'll get to talk a lot more details about the functions of cytotoxic T cells as we move forward in our course. Now, on the right over here, what we're showing you are the helper T cells and the helper T cells are also known as TH cells or CD four cells. And that's because they have CD four markers or proteins on the surface of uh these cells. And uh these helper T cells, they are different than the cytotoxic T cells. They have a different function instead of inducing apoptosis. These helper T cells are going to help activate other cells so they can activate other reinforcements if you will. And so notice over here what we're showing you are a bunch of other immune system cells that can become activated and uh they become activated by the help of the CD four cells. And so, uh the activated immune cells are gonna be capable of generating immune responses and I improved immune responses as well. And again, we'll get to talk more details about the functions of helper T cells as we move forward in our course. And notice that we're showing you the helper T cell here as a little uh uh like a crosswalk uh person that helps people cross the roads and things like that because again, it's going to be helping uh other immune cells to perform their functions better. And so uh this here concludes our brief uh introduction to the cytotoxic T cell and helper T cells. And again, we'll be able to apply these concepts as we move forward and learn more about them as well. So I'll see you all in our next video.
10
Problem
Problem
CD markers differentiate the two types of effector T cells. Cytotoxic T cells have _________ markers while helper T cells have _________ markers.
A
CD3; CD4.
B
CD4; CD5.
C
CD8; CD6.
D
CD8; CD4.
11
Problem
Problem
Which of the following statements about cytotoxic T cells is true?
A
When cytotoxic T cells encounter an antigen, they produce cytokines to stimulate other immune cells.
B
When cytotoxic T cells encounter “presented” antigens, they send signals triggering apoptosis in the infected cell.
C
When cytotoxic T cells encounter an antigen, they recruit B cells to produce antibodies.
D
Cytotoxic t cells only recognize and respond to “free” antigens.
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