So the major histocompatibility complex class two, as shown in the following diagram. So, now that the macrophage actually contains this MHC class two complex, along with this complementary antigen that came from our bacterial cell, it can basically release special types of chemicals known as interleukin one. And what this chemical does is it goes on to recruit, it calls upon helper T cells. Remember, helper T cells are special type of T lymphocyte. Now, once the helper T cell comes to this area, it basically has this receptor on the membrane that can recognize this antigen that is bound to the MHC class two complex. And once it binds, it begins to release its own chemicals.