And the macrophage engulfs that particular bacterial cell. Now, once that bacterial cell is inside the macrophage the macrophage forms the phagosome which contains lysosomes. And the lysosomes contain digestive proteolytic enzymes that break down and digest that pathogen. 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.