As a result of the presence of the MHC class two complex along with the antigen shown in red and a special type of T cell known as an inactivated helper T cell which is a CD four plus helper T cell begins to approach this MHC class two antigen. Now, what do we mean by CD four? Well, CD four is simply a special type of glycoprotein that is located on the membrane of T lymphocytes and specifically on the membrane of this inactivated helper T cell. And what this CD Four glycoprotein does is it actually binds and interacts with MHC class two. We'll see that there is another type of CD glycoprotein we call CD eight glycoprotein. And that glycoprotein only interacts and binds with MHC class one complexes, as we'll see in just a moment.