in this video we're going to begin our introduction to B lymphocytes or B cells. And so first we need to recall from some of our previous lesson videos that b lymphocytes or B cells play an important role in adaptive Hugh moral immunity. And recall that Hugh moral immunity is the part of the adaptive immune system that is going to be targeting and destroying extra cellular pathogens or pathogens that are on the outside of host cells. And these this hue moral immunity will be able to destroy these extra cellular pathogens by using B cells um as well as using what are known as antibodies. And we'll get to talk a lot more about antibodies as we move forward in our course. Now also recall from some of our previous lesson videos that dendritic cells which are antigen presenting cells or uh a pc they have both MHC Class one and MHC class two molecules. And so that means that they're capable of activating T cells uh both types of T cells the sight of toxic and the helper T cells. And when they activate the helper T cell, the helper T cell will then go on to be able to activate the B cell and then the B cell will be able to carry out its immune functions. And so if we take a look at our image down below, you'll notice it's an image that we've seen before in our previous lesson videos. And so once again we have our primary lymphoid organs at the top which include the thymus and the bone marrow, the theme. This is where the T cells fully developed and the bone marrow is where the B cells fully developed. Now notice that because we've briefly discuss the T cells already that the T cell area over here is pretty much all grayed out because we've already talked about it briefly in our previous lesson videos. And here in this video we're gonna be focusing on the B cells. And so these fully mature naive B cells will migrate from the primary lymphoid organs to the secondary lymphoid organs. And so here we have a naive or inactive B cells. Now this naive B cell has not yet encountered an antigen, but when it does encounter its antigen it will be able to internalize that anti engine process that antigen and then display that antigen on its MHC Class two molecules. And so when it's displaying those MHC Class two molecules, those antigens on those MHC Class two molecules. The effect er helper T cell can recognize those antigens on the MHC Class two. And so the defector helper T cell can then release cytokines that can ultimately activate the B cell and the activated B cell, as we've discussed before in some of our previous lesson videos are going to be able to proliferate or divide to create clones as well as differentiate into either uh Memory B cells as you see here and the Memory B cells will be important for a secondary infection or the activated B cells could differentiate into what are known as plasma cells. And plasma cells are really the defector B cell. And so these plasma cells are going to be able to release and secrete antibodies and these antibodies can carry out many different types of immune functions. And so as we move forward in our course, we're gonna talk a lot more details about this activation process of the B cells, the differentiation of the memory and the plasma cells, and then also the antibodies that these plasma cells can produce. And so this here concludes our brief introduction to these b lymphocytes or B cells, and again, we'll be able to learn more as we move forward. So I'll see you all in our next video.

in this video we're going to briefly discuss B cell receptors And so first we need to recall from some of our previous lesson videos that B cells develop in the bone marrow and these B cells have thousands of identical B cell receptors embedded in their membranes. And these B cells are also associated with what are known as antibodies. And that's because these B cells have the ability to differentiate into what are known as plasma cells that secrete many antibodies and we'll get to talk a lot more about plasma cells and antibodies as we move forward in our course. But going back to these B cell receptors, these B cell receptors are commonly abbreviated as B. C. R. S. And again each B cell is going to have thousands of identical be CRS embedded in their membrane. Now these B cell receptors Rbc Rs. These are receptors that allow B cells to recognize and attack extra cellular pathogens. Now one of the main differences between B. Cell receptors or B. C. R. S. And T. Cell receptors or T. CRS is that recall that T. C. R. S. They do not bind to free antigens. T. C. R. S. Can only bind to presented antigens on MHC. S. Now B. Cell receptors they actually can bind to free floating antigens. And so the free floating antigens are able to bind to the B. C. R. S. And when those free floating antigens bind to the B. C. R. S. They can then be internalized and processed. And then those free floating antigens can be presented by the cell for activation by helper T cells and they will be presenting those free floating antigens on their MHC Class two molecules. Now, some important things to note about these be CRS is that BC RSR practically membrane embedded antibodies. And so the structures of antibodies are going to resemble the structure of B. C. R. S and vice versa. And so they have very very similar overall structure. And we'll get to talk about the structure of B. C. R. S. And antibodies and more detail as we move forward in our course. Now, another important thing to note is that the B. C. R. S of a B cell are pretty much almost identical ah two the antibodies that that B cell eventually secretes. And so that's another important thing to keep in mind. And so if we take a look at our image down below, we can get a better understanding of these B cell receptors. And so notice on the left hand side over here we're showing you a B cell and this B cell can have again thousands of identical. Be CRS embedded in their membrane. And these are the B cell receptors. Now notice that these be crs they take on a shape that resembles that of the antibodies that they eventually produce. And again the B. C. R. S. They are capable of binding to free antigens or antigens that are not being presented. And so this is a free antigen. And again it's not it's not being presented. Now if we zoom into this BC are over here which will notice is that again the B. C. R. Is going to have this Y shaped structure that you see right here. This is our B. Cell receptor. And uh what you see here is that this little yellow region here represents the antigen binding site of the B. Cell receptor. So this is what is this is the region of the BC. Are that binds the antigen. And notice that there are two antigen binding sites allowing for the B. C. R. To bind to to uh antigens at once. And so notice over here we are showing you a free antigen and notice that it's binding to this specific episode. Tope of the free antigen. And so that's a term that we talked about in some of our previous lesson videos. And so this year concludes our brief introduction to B cell receptors and vCrs and their ability to bind to free antigens. And we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video

in this video we're going to continue our introduction to B lymphocytes by talking about the ability for naive B cells to become effect er plasma cells and memory B cells. And so first what we need to know is that before a B cell encounters a free antigen that B cell exists in an inactive form that we refer to as a naive B cell. And so once again a naive B cell is really just an inactive B cell that has not yet encountered, it's free antigen. Now upon encountering it's free antigen and then presenting that free antigen on MHC class two molecules, the naive B cells are going to be bound and activated by helper T cells. And again recall from our previous lesson videos that helper T cells can help to activate B cells. Now these activated B cells are capable of proliferating or multiplying to create identical clones of itself as well as differentiating or changing its phenotype to become either an effect er plasma cell or a memory B cell. And so the effect er plasma B cells are going to be short lived cells that make antibodies and they can make thousands of antibodies per second. So they're making lots and lots of antibodies And these antibodies as well learn moving forward in our course are capable of immediately responding to the first infection and so they are able to respond to the infection in many different ways. Now the memory B cells on the other hand these are long lived cells and they do not respond immediately to the first infection. Instead these memory B cells that are long lived cells, they somewhat remember the antigen and they're capable of making antibodies even faster and future infections. And so really they're only going to help with a future infection and help eliminate that future infection even faster than the primary infection was eliminated. And so if we take a look at our image down below, we can get a better understanding of the ability for the naive B cell to differentiate into either an effective plasma cell or a memory B cell. And so notice over here on the left hand side, what we have is a naive B cell, an inactive B cell. And when this naive B cell encounters a free antigen, as you see right here, a free floating antigen that's not being presented, this free antigen can be internalized into the B cell processed and then presented on MHC Class two molecules and the MHC Class two molecules are going to allow helper T cells to activate the naive B cells. And activation of the naive B cell will allow the naive B cell to differentiate either into a memory B cell as we see right here. Or it would allow the B cell to differentiate into a plasma cell. And the plasma cell would be the effect herself again, capable of releasing and producing thousands of antibodies per second releasing those antibodies into the environment. And those antibodies that are released into the environment can then carry out several different immune responses which again, we'll get to talk about as we move forward in our course. Now again, recall that on these B cells they have these B cell receptors or B C R. S. And the B C r. S. That a B cell has are pretty much membrane embedded versions of the antibodies that that B cell ends up producing after it differentiates into a plasma cell. And so this year concludes our brief lesson on how naive B cells can become effective plasma cells and memory cells. And once again we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video.