So it turns out that T cells that have CD four glycoproteins can only bind onto the major histocompatibility complex class two. And as we'll see in just a moment, we also have a major histocompatibility complex class one which these glycoproteins cannot actually bind to. Now, the question is what exactly takes place when this binding is initiated? So basically, once the binding process takes place, the T cells can stimulate our immune system in two different ways. They can either stimulate the humoral immunity or they can stimulate the cell mediated immunity. So let's suppose the CD four T cell that binds onto the APC is a helper T cell in such a case when this binding process takes place.