And they mount a defensive response. They label those cells for destruction and begin destroying that allograph altogether. So, once again, when a tissue or organ is transplanted it has a very high chance of being rejected by the host individual. Recall that our immune system attacks anything that it recognizes as foreign or pathogenic. And if the major histocompatibility complex MHC self antigens of the transplanted tissue cells do not match or not compatible with the host cells, then the host immune system will mount a defensive response and destroy that allograph. And we see that take place in the following diagram.