in this video we'll talk about T Cell Activation T Cell Activation take place when T Cell interacts with the antigen presenting cells such as the dendritic cell before understanding the cellular and molecular events in T Cell Activation let us begin from the basics T Cell develops in the bone marrow and it all starts from the hematopoietic pluripotent stem cell from there it develops into lymphoid progenitor from the lymphoid progenitor T Cell precursors are generated and they leave the bone marrow to reach the thymus and in the thymus there is stringent training that these T Cell
precursors get once these T-cell precursors leave the thymus they have T cell receptors and a co-receptor in this case CD4 but these cells are actually naive T cells that means they have not encountered any antigens so far and they are right now in a quiescent state that means in g0 phase these T cells are circulating that means they get circulated into the bloodstream and move here and there anyway at this point of time T cells has condensed chromatin not much transcriptional activity is going on in these T cells and they have very little proportion of
cytoplasm as well now these cells move from one place to another throughout the body and they possibly encountered the dendritic cell in this process it it is found that these T cells are circulating among the blood lymph node and the secondary lymphoid tissue in every 24 hours in this time course they can possibly encounter a dendritic cell let's see what happens in this encounter dendritic cells are antigen presenting cells that means they can present an antigen on top of Class 2 MHC molecule this class 2 MHC molecule can be recognized by T Cell receptor this
T Cell receptor mediated signaling is really important for T Cell Activation indeed this is the first signal that is required for a T Cell Activation there are other receptors present in the T cells such as cd28 which is a cost-stimulatory receptor it interacts with the CD 80 or cd86 receptors on the tendritic cell and this interaction gives the signal 2 for activation other than these two interactions the cytokine signaling is the third signal which leads to a T Cell Activation and the key cytokine for T Cell Activation is interleukin-2 once there are three signals like
this the T cell would now re-enter the cell cycle they would proliferate rapidly this is known as clonal expansion after proliferating rapidly they could be differentiated into several sub lineages based on the cytokines they encounter they could become th1 cell th17 cell T follicular cell or even th2 cells even some of them become T memory cell in future if you want to learn in this process in details that means the T cell differentiation process in details the link is found in the I button or in the description now let me tell you that in T
cells cd28 are not the only co-stumulatory receptor along with cd28 icos is another co-stimulatory receptor now icos can interact with the icos ligand present in the activated dendritic cells and these kind of interaction is super important for the effector T cells now the naive T cell does not express the icos molecule but effector T cell does it is also found in the memory T cells it is thought that these icos receptors are required for maintaining activated state now the positive stimulation is not the only type of interaction that happens in case of a T cell
there are negative core stimulatory receptor as well such as ctla now the ctla and cd80 interaction leads to an inactivation of T Cell responses that means these uh positive and negative co-stimulatory receptors maintain a balance of T cell activity indeed there are several negative core stimulatory receptor present in the T cell and these negative co-stimulation ensures that T cell hyperactivation can be prevented now in summary we learned that T Cell Activation requires the interaction between antigen presenting cells like dendritic cells and T cells there are three distinct signals which are required for the activation of
T cells and we learned about all of them and we learned the importance of cytokine interleukin-2 we also looked at T cell has positive and negative co-stimulatory receptor and we learned that once activated they can be differentiated into different subclasses so if you want more videos and notes lectures all of these can be found in my Facebook page or in my Instagram page my handle is provided here it the links are provided in the description you can support our channel in patreon or in beam UPI also under each video there is an option for super
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