hello and welcome to learn a double Bhaiji for free with miss astrick today's video is on the cell mediated response or cellular response of immunity and this focuses on the T lymphocytes and the T cells if you are new here then make sure you click subscribe to keep up to date with all the latest videos and if you do like today's video then please give it a thumbs up if you want to make notes as you go 3 then to grab a pen and paper now and pause whenever you need to so the T lymphocytes or T cells for short these are involved in the specific immune response so this is the second line of defense after a pathogen has got into the bloodstream so all lymphocytes are made in the bone marrow the reason that these are called T cells though is because the T cells mature in the thymus and the thymus is this organ just here the cell mediated response is the response involving the T cells so that's what we're going to be focusing on today and when we say specific immune response we mean it is the response to an exact antigen or cell surface molecule so antigen presenting cells now I briefly mentioned this in the first video in immunity if you've not seen that then just click it so you can see that one first APC for short now these are any cell that presents a non-self antigen on their cell surface membrane so that could be an infected body cell which has a virus inside and that will then present the viral antigen on the cell membrane or it could be one of the phaedra sites such as a macrophage after phage site ASIS and it is engulfed and destroyed a pathogen and will then present the antigens on its surface it could be cells of a transported organ which will also have different shaped antigens compared to your ownself cell antigens or abnormal cells such as cancer cells they will also have slightly different shaped self cell antigens so all of these would class as antigen-presenting cells and is these cells which trigger B cell mediated response but first why it is called cell mediated instead of just the T cell response well it's called the cell mediated response because it is just do the T cells but the T cells will only respond to antigens which are presented on antigen presenting cells so it's cell mediated because it's only the response of T cells to antigens on the outside of the membrane of cells it won't be the T cells will not be responding to any antigens which are just floating in the blood or other bodily fluids say what the response actually is then step one once a pathogen has been engulfed in phaedra cytosis the antigens will then be placed on the surface of that phaedra site or macrophage and that is now an antigen presenting cell so we've got an antigen presenting cell just here the helper T cells which are a type of T lymphocytes they actually have receptors on their surface and those receptors are able to bind to antigens which are being presented on the antigen presenting cell now when that happens when they attach together it activates these helper T cells and that activation causes them starts divide by mitosis and they will then replicate to make large numbers of claims so this diagram here is actually going into more detail than you need but it's just gives you an overall idea of this attachment and between the receptor and the aunt in step four that's not the end so step four we've now had lots and lots of mitosis to create this large number of T helper cells and those will then differentiate into different cells or stimulates different cells so one thing that could happen is some of those cells will remain how the T cells and they will then go on to activate b-cells the b-cells are in the humoral response which is going to be in a later video some will stimulate macrophages which are the fader sides which will then undergo fader cytosis and destroy any pathogens son will become memory cells and they will store memory of that particular shaped antigen some will become slides toxic T cells or killer T cells and that's what we're going to focus on next these killer T cells or cytotoxic cells say cytotoxic T cells these can destroy abnormal or infected cells what they will do is release a protein and this protein is called perforin perforin is able to embed into the cell surface membrane of whichever infected cell and it's attached to and when it does that actually makes a pore or hole in that cell surface membrane and the result of that is any substance can enter or leave the cell and that causes cell death so this is most common environment sections because viruses will replicate within your body cells so as a results the sites of toxic T cells were released as per foreign that embeds into your cells cell surface membrane causing your own body cells to die but that is the sacrifice to prevent the virus from being able to replicate and infect even more of your body cells so just an example down here when you have a bad cold and you have a sore throat the reason you actually have a sore throat is the cytotoxic T cells are destroying the cells in the back of your throne which are infected with the virus and if they can then destroy all of the infected cells then that will mean it can't replicate further and it can't go on to cause any more damage so in summary the cell-mediated response involves the response of t lymphocytes to antigens on the cell's antigen presenting cells could be fade asides abnormal self cells non-self cells were transplant or infected body cells helper T cells divide by mitosis to become more helper T cells which will then stimulate the B cells and fade recite ASIS or they could become team memory cells or cytotoxic T cells cytotoxic T cells will kill the infected body cells by releasing perforin and that protein creates pores in the cell surface membrane which causes a cell to shrivel or lice so that is it for the cell mediated response for practice questions head over to miss Esther ich komm and if you have found this helpful today then please do give it a thumbs up