in this video we're going to do a review of adaptive immunity by outlining and discussing this image that you see down below which is an image that we've discussed briefly before in some of our previous lesson videos. And so notice that towards the top of this image in this little box at the top we have the primary lymphoid organs which recall includes the thymus which is where the t cells fully developed and mature and the bone marrow which is where the B cells fully developed and mature. And so notice on the left we have a T cell and on the right we have a B cell. Now notice that after the B cells and T cells have fully matured in the primary lymphoid organs, they can then migrate to the secondary lymphoid organs. And that is what this green box here represents. And so notice that initially the T cells and the B cells are going to exist in their naive states. And so here we have a naive psycho toxic T cell or TC cell, a naive helper T cell or th cell and a naive B cell. And recall that the naive term just refers to the inactive forms of these T cells and B cells. And so what that means is that the naive forms need to become activated before they can generate an immune response. And the way that they become activated is by encountering their very specific antigen that they respond to. Now recall for the T cells that they need to be presented an antigen. And that's because the T cell receptors or T cRS can only recognize antigens that are presented to them on MHC s and so an antigen presenting cells such as a dendritic cell which we're showing you over here so we can go ahead and label this as our dendritic cell. This dendritic cell can present antigens to the naive T cells and therefore activate the naive T cells. And so recall that the dendritic cell is capable of taking samples from its environment and then presenting those antigens on its surface on MHC s. And the dendritic cell has both MHC Class one and MHC Class two. Recall that the MHC class one is used to present to cida toxic T cells or T C cells. And the MHC class two is used to present to the naive helper T cells. And so here in the center of our image notice we're showing you are dendritic cell presenting antigens on its surface to the side a toxic T cell and the helper T cell. And also recall from our previous lesson videos that uh these co stimulatory molecules that are produced by the dendritic cell are going to be important for also activating the T cells as well. And so notice that once the T cells become activated, they're capable of dividing and proliferating to create an army of identical clones. And they're also capable of differentiating into different cell types and those different cell types include affect their cells and memory cells. And so notice that the site a toxic T. Cell that is activated here. Not only does it divide and proliferate, it is also going to differentiate into different cell types. It could differentiate into memory site a toxic T cells which are going to remain in the secondary lymphoid organs and be important for generating a response to a future exposure to the same exact antigen, creating an even stronger response when we are encountering the same antigen in the future. Um or the T cell could differentiate into an effect er side a toxic T cell which is going to respond to the primary uh exposure to the antigen. And so these defectors cida toxic T cells what they do is they induce a popped oh sis of cells that are infected with uh an intracellular pathogen. And so notice that here we have an infected host cell that is infected with a virus. And so the effective T. Cell can come and induced apoptosis in this infected cell. And by inducing apoptosis and killing that infected host cell it helps to limit the spread of the pathogen. Um Now for the helper T cells the helper T cells have somewhat of a different function than the site a toxic T cells. And so instead of inducing apoptosis the helper T cells are more about activating other immune cell components. And so when the helper T cell becomes activated by the dendritic cell presenting antigens to it. The helper T cell again can proliferate or divide to create an army of identical clones and it can also differentiate into either memory helper T cells which again are going to be important for generating an immune response to future um exposures to the same exact antigen. Or it could differentiate into an effect er helper T. Cell And again the effect of helper T cell is important for activating other types of cells. Here in this image you can see right here this effective helper T cell is important for activating the B. Cell but also the effect of helper T cell can also be important for activating other immune cells such as macrophages for example and activating macrophages have increased killing power, increased destructive abilities to eliminate pathogens. And so notice here we're saying that this helper T cell is capable of activating macrophages and B cells as well by releasing cytokines, chemicals that allow for the macrophage to become activated. Uh And also again here the cytokines are not being shown but the effect of T. Cell can release cytokines to activate the B. Cell. And so if we turn our attention to the B cells again initially the B cells are going to be in their naive form an inactive form before they have encountered the antigen. But as soon as they are and as soon as they are exposed to their very specific antigen um there B cell receptors can bind to that antigen internalize that antigen process it and then express that antigen on MHC s on its surface specifically MHC Class two. And so the effect er helper T cell can recognize that antigen presented on the MHC Class two and it can then activate the naive B cell uh and make it an activated B cell. And the activated B cell Of course it's going to divide and proliferate to create an army of B cells. Um and it can also differentiate into plasma cells or memory B cells. Again the memory cells are really really important for generating a response to a future exposure to the same antigen. So it creates a faster response upon future infections. Uh and the plasma cells are all about secrete ng antibodies and the antibodies can lead to a variety of different immune responses. And so notice that here we have a plasma cell secreted hundreds or thousands of antibodies per second in response to uh an antigen. And so here we're saying that the antibodies are being released by the plasma cells and again they can have many different immune responses. For example tagging pathogens for removal. And so notice here we have the antibodies binding to a pathogen in order to eliminate that pathogen. And so one of the most important components of adaptive immunity is the memory component. The fact that it is able to generate a bunch of memory cells that are going to be able to respond even better to a future infection. And another important component about the adaptive immune system is that it is very, very specific. Each individual T. Cell and each individual B cell can only respond to one very specific antigen. And so it's important for us to have a wide diversity of many different types of T cells and many different types of B cells so that we can respond to a wide variety of different antigens. And so this here concludes our brief review of adaptive immunity and we'll be able to apply some of these concepts as we move forward in our course. And so I'll see you all in our next video.