So here we have an infected cell. Now, what the infected cell will do is it will take a certain antigen that came from that pathogen and it will display it on this MHC protein complex. So the major histocompatibility complex as shown. Now, in some cases the pathogenic antigen that is displayed on our membrane that came from that pathogen might resemble some other self antigen that is found on healthy cells of our body. So we have two healthy cells in some place in our body. And notice that these green cell antigens which are normally seen by the white blood cells as normal resemble the pathogenic antigen.