In this video, we're going to begin our lesson on major histocompatibility complexes. But before we define what those are, it's first helpful to note that immune cells must properly identify threats and only target infected host cells and pathogens, which are dangerous to us. However, our immune cells should not be targeting uninfected or healthy host cells that are harmless to us. And so one of the ways that T cells can detect threats is by interacting with really special molecules on our host cells that are called MHCs. And so these MHCs are, is really just an abbreviation for major histocompatibility complexes. And these major histocompatibility complexes or MHCs can be defined as surface proteins on our host cells that present antigens to T cells, and then those T cells can then generate an appropriate immune response.
Now, if we take a look at our image down below, what you'll notice is that on the left-hand side over here we're showing you a macrophage which is an example of one of our own host cells. Notice that on the surface of our macrophage are these little molecules here and this little molecule that you see right here is a major histocompatibility complex or in other words, an MHC. Now notice that these MHCs, what they do is they present antigens. And so notice here these are being labeled as antigens. And they are presenting antigens to these T cells. And over here on the right, what we have is a helper T cell, a TH cell. And remember that this is also known as a CD4 cell. And, of course, this helper cell can use its TCR or T cell receptor in order to detect the MHC presenting an antigen. And, of course, that will allow for the helper T cell to generate an appropriate immune response, which we'll get to talk more details about as we move forward in our course.
Now it does turn out that there are 2 major types of major histocompatibility complexes, and we'll be able to talk about those 2 major types as we go forward. So I'll see you all in our next video.