In this video, we're going to briefly discuss B cell receptors. First, we need to recall from some of our previous lesson videos that B cells develop in the bone marrow. These B cells have thousands of identical B cell receptors embedded in their membranes. These B cells are also associated with what are known as antibodies. That's because these B cells have the ability to differentiate into what are known as plasma cells that secrete many antibodies. 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, they are commonly abbreviated as BCRs. Each B cell is going to have thousands of identical BCRs embedded in their membrane. B cell receptors or BCRs, are receptors that allow B cells to recognize and attack extracellular pathogens.

One of the main differences between B cell receptors, or BCRs, and T cell receptors, or TCRs, is that TCRs do not bind to free antigens. TCRs can only bind to antigens presented on MHCs. B cell receptors, however, can bind to free-floating antigens. The free-floating antigens are able to bind to the BCRs. When those free-floating antigens bind to the BCRs, they can then be internalized and processed, and those free-floating antigens can be presented by the cell for activation by helper T cells. They will be presenting those free-floating antigens on their MHC class 2 molecules. An important note is that BCRs are practically membrane-embedded antibodies. The structures of antibodies and BCRs are very similar.

We will discuss the structure of BCRs and antibodies in more detail as we move forward in our course. Another important thing to note is that the BCRs of a B cell are almost identical to the antibodies that B cell will eventually produce. This leads to a better understanding of these B cell receptors. Notice on the left-hand side over here, we're showing you a B cell. This B cell can have, again, thousands of identical BCRs embedded in their membrane, which are the B cell receptors. These BCRs take on a shape that resembles that of the antibodies they eventually produce. The BCRs are capable of binding to free antigens. This is a free antigen, and it's not being presented. If we zoom into this BCR over here, you'll notice the Y-shaped structure. This shows our B cell receptor, and the little yellow region here represents the antigen-binding site of the B cell receptor. This region of the BCR binds the antigen. Notice that there are two antigen-binding sites allowing for the BCR to bind to two antigens at once. We are showing you a free antigen binding to this specific epitope of the free antigen. This concludes our brief introduction to B cell receptors and BCRs and their ability to bind to free antigens. We'll be able to get some practice applying these concepts and learn more as we move forward in our course. I'll see you all in our next video.