Functions of T Lymphocytes - Video Tutorials & Practice Problems

Functions of Cytotoxic T Cells

In this video, we're going to talk more details about the functions of T lymphocytes. And in this video, we're going to first start off by talking about the functions of cytotoxic T cells or TC cells. And then later in our lesson in a different video, we'll talk about the functions of the helper T cells. Now first we need to recall from some of our previous lesson videos that cytotoxic T cells or TC cells are important for targeting infected host cells that are presenting intracellular pathogens or antigens from inter intracellular pathogens on MH C class ones. And these cytotoxic T cells will induce apoptosis in these infected host cells, eliminating the infected host cell and ultimately eliminating the the in intercellular pathogen within them as well. Now, these cytotoxic T cells have the ability to distinguish between uninfected healthy host cells and infected dangerous host cells and they can do that by what is being presented on the MH C class one molecules on uninfected cells or healthy host cells. These are going to present non immunogenic self-made peptides. And so what that means is that these are going to be presenting normal uh proteins that belong to us on their MH C class ones and self made peptides are non iogen, which means that they do not elicit an immune response. And so again, we know from our previous lesson videos that these T cells would become allergic or unresponsive if they did target uninfected cells. Now infected cells that are infected with some kind of intracellular pathogen like for example, a virus, these are going to be presenting uh immunogenic antigens, immunogenic microbial antigens and immunogenic microbial antigens. As their name implies, they do elicit an immune response or they do cause an immune response. And those are gonna be the ones that the T cells are gonna be uh focusing their uh immune response on the infected cells. And so when a cytotoxic T cell binds an infected cell presenting an immunogenic microbial antigen, that cytotoxic T cell is going to release a series of proteins and molecules uh like for example, proteases which are proteins that degrade other proteins and perforin, which is uh referring to molecules that are capable of creating pores in the infected cell. And these pores in the infected cell allow proteases to enter into the infected cell via those pores. And again, these proteases are proteins themselves that degrade cellular proteins within the infected cell. And by degrading all of these cellular proteins within the infected cell that ultimately will induce apoptosis in the infected cell. And so by the cytotoxic T cell inducing apoptosis and infected cells. Uh apoptosis is a way to control the killing of infected cells without exposing the pathogens to nearby healthy cells. And so uh these cytotoxic T cells, they can also release cytokines or communicating molecules to neighboring cells, activating macrophages and increasing antigen presentation on dendritic cells ultimately helping to boost the immune response even more. And so, if we take a look at our image down below, we can get a better understanding of the functions of these cytotoxic T cells. And notice that our image is broken up into two sections. We have the top section here in blue and then we have this bottom section down below here in pink. And what you'll notice is that in the top section, what we have is an uninfected cell. This is a healthy cell and it is going to be presenting normal cytoplasmic proteins on its MH C class one. And so, because this uninfected cell is presenting normal proteins, this cytotoxic T cell over here is or TC cell or CD eight cell. In other words, is not going to generate an immune response towards these uninfected healthy cells. And so no immune response is generated here. However, if the cytotoxic T cell over here recognizes uh these uh microbial antigens, uh these dangerous microbial antigens like for example, antigens from a virus, uh then it will be able to uh determine that this is an infected host cell. Uh And again, that is because this infected host cell is presenting immunogenic microbial antigens or microbial antigens that are capable of generating an immune response. And so the cytotoxic T cell again, will release, the proteases will release the Perin. And uh notice that it will allow these molecules uh which sometimes are referred to as death packages. Uh allow those molecules to enter into the effect infect itself and cause apoptosis of the infected cell. And again, by causing apoptosis of the infected cell, it gets rid of the infected cell, but it also helps to get rid of and eliminate the pathogen that is inside of it. And so it is a way to help defend ourselves from the pathogens. And so this here concludes our brief introduction to the functions of cytotoxic T cells and their ability to cause apoptosis in infected cells. And we'll be able to get some practice applying these concepts and then talk about the functions of helper T cells as we move forward in our course. And so I'll see you all in our next video.

Which statement is FALSE about cytotoxic T cells?

• A. They stimulate B cells.
• B. They destroy virus-infected cells.
• C. They recognize MHC I bound antigens on APCs.
• D. They induce apoptosis in infected cells.

$T_c$ cells recognize epitopes only when the latter are held by

• A. MHC proteins.
• B. B cells.
• C. Interleukin-2.
• D. Granzyme.

Types of Helper T Cells

In this video, we're going to briefly introduce some of the different types of helper T cells or TH cells. And so, depending on the signals provided by a dendritic cell, the naive helper T cells can differentiate into one of many different effector helper T cell subtypes. And so we're not going to cover all of the possible helper T cell subtypes. Uh but down below notice, we have a table with three of the different subtypes of helper T cells. And so each subtype of effect or helper T cell can produce different cytokines or communicative signals that can control an immune response in slightly different ways. And so if we take a look at our image down below of this table of the types of helper T cells, notice that we're showing you three different types, th one th two and th 17 cells. And again, there are many, many types that are not being listed here. And so we're only gonna briefly cover these three to give you a sense for uh what this could look like. And so for these uh th one cells, these are cells that respond to intracellular pathogens. And so uh for example, viruses uh that are infecting a cell and they can do so by activating macrophages and also by activating cytotoxic T cells or TC cells. And we know that cytotoxic T cells target intracellular pathogens. And so uh sometimes these helper T cells can actually help to activate other T cells, uh other cytotoxic T cells. And then uh this is an example of a class of helper T cell that's capable of doing that. Now, the th two cell uh as you can see here, these can actually respond to multicellular pathogens, for example, helmets, these uh worms and uh they're multicellular and they can do so by recruiting and activating eosinophils and basophils which again can target these multicellular pathogens like helmets and then notice that the th 17 helper T cells, those can respond to extracellular pathogens or pathogens on the outside of cells like for example, bacteria that are on the outside of cells by recruiting and activating neutrophils. And again, these neutrophils can uh go on to uh target these bacteria, uh these extracellular pathogens and eliminate them. And so again, there are a variety of different helper T cells, all with slightly varied functions. However, it is important to note that moving forward in our lesson, we are going to consider the functions of all helper T cells subtypes as a group collectively. So we're not gonna focus in on any individual one of these uh subtypes of helper T cells. We'll be focusing on them collectively as a group. And so that being said, this year concludes our brief introduction to some of the different types of helper T cells. And we'll be able to get some practice and learn more as we continue to move forward in our course. So I'll see you all in our next video.

Functions of Helper T Cells: Activation of Macrophages

In this video, we're going to talk more generally about the functions of helper T cells or th cells. And we're going to focus specifically on the activation of macrophages. Now, first, we need to recall from some of our previous lesson videos that naive helper T cells or inactive helper T cells can become activated by dendritic cells that are uh antigen presenting and presenting antigens on their MH C class two molecules. Now, unlike the cytotoxic T cells, whose function is to mainly induce apoptosis and infected cells, helper T cells don't induce apoptosis in other cells. Instead helper T cells or th cells, they are going to make cytokines or communication signals that ultimately help to stimulate and activate other immune cells, improving the immune capabilities of immune cells around it. And so it can improve or activate the immune cells such as macrophages, naive cytotoxic T cells and B cells as well. Now, here in this video, we're going to specifically focus on the ability for helper T cells to activate macrophages. And so macrophages, they are routinely engulfing, degrading and processing invading pathogens in many of our different tissues. And so this is something that they do on a routine basis. And uh what they can do is they can also present uh these pathogens as antigens on their Mh C class two molecules. Now, effector helper T cells are capable of binding to the antigens presented on MH C class two. And that will activate the helper T cells. And the activated helper T cells again will produce cytokines that are capable of activating other immune cells or uh activating or stimulating the macrophages even further improving their uh immune capabilities. And so these stimulated or activated macrophages have increased production of lysozyme, which we call are organelles involved with the uh destruction, degrading and also increased production of antimicrobials that can destroy invaders more effectively. And so the helper T cell helps the macrophage uh destroy invaders more effectively. Now, the helper T cells can also release additional cytokines that can activate nearby cytotoxic T cells as well. And so ultimately, these helper T cells help to boost and enhance the immune response to get rid of invaders even better. And so if we take a look at our image down below, we can get a better understanding of the functions of these helper T cells. Now notice on the left over here, what we're showing you is a um uh a uh macrophage. And so really the top half of this image here is just a cartoon version of another. They're showing the same thing just in a different way. And so what we have is a macrophage and uh the macrophage is not yet activated. And so these macrophages, they are commonly and routinely uh engulfing degrading and processing pathogens. So, they have an invading pathogen here and the macrophage will engulf it degrade it, break it down and then present it on its surface um at on these MH C class two molecules. And so you can see here, our macrophage is presenting the antigens on its MH C class two molecules. And so uh what you'll notice is that when a helper T cell recognizes the antigen on an MH C class two molecule, the helper T cell can release cytokines. And uh these cytokines here can have an impact on the macrophage and it can activate the macrophage. And so notice here we have our helper T cell is somewhat presenting these cytokines to the macrophage and the macrophage is taking it in and that improves the destructive capabilities of the macrophage so that we have a, an activated or stimulated macrophage. And so now it's capable of killing the invaders even more effectively. And so, uh down below what we're showing you is again, the activated or the stimulated macrophage with improved uh destructive immune abilities. And so really, that's what these helper T cells do. They help other immune cells improve their uh destructive immune abilities even further. And so this year concludes our brief lesson on the general functions of helper T cells and their ability to activate macrophages. And 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.

Why are cytokines important signals for cell-mediated immunity?

• A. Cell-mediated immunity requires immune cells to communicate to perform most efficiently.
• B. Cytokines are signals that allow immune cells to communicate.
• C. Effector cells, like CD4 cells, use cytokines to activate other immune cells.
• D. Cytokines signal to specific immune cells to increase their destructive properties and destroy pathogens.
• E. A and B.
• F. C and D.
• G. All of the above.

T______ cells assist in the functions of certain B cells and other T cells.

• A. sensitized.
• B. cytotoxic.
• C. helper.
• D. natural killer.

Which type of helper T cells are involved in fighting extracellular pathogens?

• A. $T_H1$
• B. $T_H2$
• C. $T_H17$
• D. A and B.
• E. B and C.
• F. All types of helper T cells help fight extracellular pathogens.