And then let's discuss some of the methods that medical professionals actually use to fight these different complications that arise from transplantation. So let's begin with graft rejection and let's first recall how our immune system actually works. So recall that the entire goal of our immune system, the entire goal of wide blood cells is to be able to differentiate between our own host healthy cells and infected cells or pathogens that might make their way into our body. So our wide blood cells use something called the major histocompatibility complex and self antigens to basically distinguish our whole cells from infected cells or pathogens. Now, the problem with grafting or transplantation is when we actually transfer that tissue or that organ, the tissue or the organ on the other individual might have different major histocompatibility complexes and different self antigens. And if these antigens are not compatible, if there is no match, then what the wide blood cells of that host immune system do is they recognize those other cell antigens of the other individual as pathogenic, as being foreign.