Now, the primary reason, the primary thing that creates these complications is actually the immune system of that host individual that is accepting that graft or that organ. So let's discuss some of the major issues involved with transferring grafts as well as organs from one individual to a different individual. So let's examine graft rejection, let's discuss graft versus host disease and also infections. 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.