Functions of T Lymphocytes

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 Cida toxic T cells or T. C 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 cida toxic T cells or T C cells are important for targeting infected host cells that are presenting intracellular pathogens or antigens from into intracellular pathogens on MHC class ones. And these side a toxic T cells will induce apoptosis in these infected host cells, eliminating the infected host cell and ultimately eliminating the the intracellular pathogen within them as well. Now these side a toxic 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 MHC class one molecules on uninfected cells or healthy host cells. These are going to present non immunogen IQ self made peptides. And so what that means is that these are going to be presenting normal proteins that belong to us on their MHC class ones and self made peptides are non immunogen in 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 a non ergic 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 ah immunogen inc antigens, immunogen inc microbial antigens and immunogen inc 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 going to be focusing their immune response on the infected cells. And so when a site a toxic T cell binds an infected cell presenting an immunogen inc microbial antigen that cida toxic T cell is going to release a series of proteins and molecules like for example, protea aces which are proteins that degrade other proteins and perforated, which is referring to molecules that are capable of creating pores in the infected cell. And these pores in the infected self allow Proteus is to enter into the infected cell via those pores. And again these protea aces are proteins themselves that degrade cellular proteins within the infected self. And by degrading all of these cellular proteins within the infected self that ultimately will induce apoptosis in the infected cell. And so by the side a toxic 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 these side a toxic 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 side a toxic 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 MHC Class one. And so because this uninfected cells presenting normal proteins, this psycho toxic T cell over here is or T. C. 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 site a toxic T cell over here recognizes these microbial antigens, these dangerous microbial antigens like for example antigens from a virus, then it will be able to determine that this is an infected host cell. And again that is because this infected host cell is presenting immunogen IQ microbial antigens or microbial antigens that are capable of generating an immune response. And so the site a toxic T cell again will release the proteus is will release the preference and notice that it will allow these molecules which sometimes are referred to as death packages, 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 cida toxic 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.

Tc cells recognize epitopes only when the latter are held by

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

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 defector helper T cell subtypes. And so we're not going to cover all of the possible helper T cell subtypes. But down below notice we have a table with three of the different subtypes of helper T cells. And so each subtype of effective 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 going to briefly cover these three to give you a sense for what this could look like. And so for these th one cells these are cells that respond to interest cellular pathogens. And so for example viruses that are infecting a cell and they can do so by activating macrophages and also by activating psycho toxic T cells or T. C cells. And we know that psycho toxic T cells target intracellular pathogens. And so sometimes these helper T cells can actually help to activate other T cells other side a toxic T cells. And then this is an example of a class of helper T cell that's capable of doing that. Now the th two cell, as you can see here, these can actually respond to multi cellular pathogens. For example helmets, these worms and they're multicellular and they can do so by recruiting and activating NGO cinephiles and bestow fills which again can target these multicellular pathogens like helmets. And then notice that the th 17 helper t cells, those can respond to extra cellular 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 go on to target these bacteria uh these extra cellular 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 going to focus in on any individual. One of these subtypes of helper T cells will be focusing on them collectively as a group. And so that being said this here concludes our brief introduction to some of the different types of helper T cells and will 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

in this video we're going to talk more generally about the functions of helper T cells or T. H 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 antigen presenting and presenting antigens on their MHC Class two molecules. Now unlike the cida toxic T cells whose function is to mainly induced apoptosis and infected cells, helper T cells don't induce apoptosis and other cells. Instead helper T cells or th cells they are going to make cytokines or communication signals that ultimately helped 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 side A toxic 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 that they do on a routine basis. And what they can do is they can also present uh these pathogens as antigens on their MHC class two molecules now affect their helper T cells are capable of binding to the antigen is presented on MHC 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 activating or stimulating the macrophages even further improving their immune capabilities. And so these stimulated or activated macrophages have increased production of Lissa simes which recall are organelles involved with destruction degrading and also increased production of antimicrobials that can destroy invaders more effectively. And so the helper T cell helps the macrophage destroy invaders more effectively. Now the helper T cells can also release additional cytokines that can activate nearby side a toxic 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 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 the macrophages not yet activated. And so these macrophages they are commonly and routinely 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 on these MHC class two molecules. And so you can see here our macrophage is presenting the antigens on its MHC class two molecules. And so what you'll notice is that when a helper T cell recognizes the antigen on an MHC Class two molecule, the helper T cell can release side all kinds and 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 macrophages taking it in and that improves the destructive capabilities of the macrophage so that we have an activated or stimulated macrophage. And so now it's capable of killing the invaders even more effectively. And so down below what we're showing you is again the activated or the stimulated macrophage with improved destructive immune abilities. And so really that's what these helper T cells do. They help other immune cells improve their 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.