All pathogenic antigens that eventually make their way into the tissues of our body must be presented to tillymphocytes the cells of our cellmediated immunity. The problem is these telemphicides cannot actually directly bind onto these antigens. What must happen before these T lymphocytes interact with the antigen is a special type of immune cell known as the antigen presenting cell must actually engulf our antigen. And once it engulfs the antigen it takes that antigen and it places it onto a special protein complex found on the membrane of the antigen presenting cell. And this protein complex is known as the major histocompatibility complex class Two or simply a MHC Class Two. And only when the antigen is bound to this MHC Class Two complex can the lymphocyte actually see and interact with the antigen and bind onto this antigen.