And what this cytotoxic T cell does specifically is it binds onto this complex and it initiates the release of powerful digestive proteins. And those proteins drill holes in the membrane of these grass cells and that ultimately lyses and destroys the cell. So this is the major problem that is involved with the transplantation and grafting process, the actual immune system of that host organism, host individual destroying that transplanted tissue or organ. Now, another important complication is actually the opposite of this. So this is called graft versus host disease or gvhg. So let's suppose we're transplanting some type of tissue or organ from one individual to a different individual.