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, these B cell receptors are commonly abbreviated as BCRs. Again, each B cell is going to have thousands of identical BCRs embedded in their membrane.

Now, these 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, recall, TCRs do not bind to free antigens. TCRs can only bind to presented antigens on MHCs. However, B cell receptors can actually bind to free-floating antigens. The free-floating antigens are able to bind to the BCRs. When these free-floating antigens bind to the BCRs, 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, presenting those free-floating antigens on their MHC class 2 molecules.

Some important things to note about these BCRs is that BCRs are practically membrane-embedded antibodies. The structures of antibodies are going to resemble the structure of BCRs and vice versa, and they have very similar overall structures. We'll get to talk about the structure of BCRs and antibodies in more detail as we move forward in our course.

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, these are the B cell receptors. Notice that these BCRs take on a shape that resembles that of the antibodies they eventually produce. The BCRs are capable of binding to free antigens, antigens that are not being presented. If we zoom into this BCR over here, what you’ll notice is that the BCR has a Y-shaped structure you see right here. This is our B cell receptor, and this yellow region represents the antigen-binding site of the B cell receptor. This is the region of the BCR that binds the antigen. Notice that there are two antigen-binding sites allowing for the BCR to bind to two antigens at once. We're showing you a free antigen and notice that it's binding to this specific epitope of the free antigen.

This concludes our brief introduction to B cell receptors (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.