MHC molecules present viral protein fragments on infected cells as flags for CD8 T-cells to identify and destroy them.

“a killer t-cell will come along and it will see let's say it has ten cells in front of it five of them have been infected with HIV and five of them have not so it'll move over them it has on its surface a t-cell receptor that looks like an antibody it'll move over and look at the buckets and say okay I've got five uninfected cells here I'm not going to kill these guys but then it comes to an HIV infected cell and it sees a piece of the virus in one of these buckets and it goes crazy it binds to that and then it blows holes in that infected cell and it closes the factory down”