So basically, the GP 120 glycoprotein of HIV binds to a specific glycoprotein receptor found on membrane of immune cells. And this special type of glycoprotein is called CD four glycoprotein. So HIV contains a glycoprotein, the GP 120, that can bind onto the CD four protein of immune cells are white blood cells. Now, recall from our discussion on white blood cells and specifically on T lymphocytes, we said that one of the specialized types of T lymphocytes that contains a CD four glycoprotein are the helper T cells of our adaptive, our acquired immune system. So recall that helper T cells are CD four positive cells. And what that means is these HIV agents will be able to bind and will be able to attack these helper T cells.