Now, it turns out that we know much more information about AlphaBeta T cells than we do about gamma delta T cells. And that's exactly why in this lecture we're going to focus primarily on alpha beta T cells. Now, before we take a look at these alpha beta T cells let's recall what an antigen presenting cell is or an APC. So an antigen presenting cell is a type of white blood cell whose function is to engulf our antigens and take those antigens and present those antigens on the membrane of those APCs. So basically, these antigen presenting cells contain these protein complexes on the membrane known as the major histocompatibility complex. And what these protein complexes do is they're capable of binding these antigens that the cells actually engulf.