Now, when digestion takes place what the macrophage does is because it's an antigen presenting cell it begins to build the MHC class Two complex. And it takes that complex and places it on the membrane of the macrophage. And then it takes a small peptide, the antigen from that bacterial cell and it places it on that MHC class II complex. So we have this antigen MHC class Two complex that forms. Now, as soon as this actually takes place we have a special type of T lymphocyte whose membrane contains a special glycoprotein known as CD four. Only T lymphocytes that contain the CD four glycoprotein can actually go on and bind onto the antigen MHC class II complex.