An immune response to a tissue graft will differ from an immune response to a bacterium because A) MHC molecules of the donor may stimulate rejection of the graft tissue, but bacteria lack MHC molecules. B) the tissue graft, unlike the bacterium, is isolated from the circulation and will not enter into an immune response. C) a response to the graft will involve B cells and a response to the bacterium will not. D) a bacterium cannot escape the immune system by replicating inside normal body cells. E) the graft will stimulate an autoimmune response in the recipient.