54. What complications will arise if the blood of an Rh +ve person is transferred to a Rh -ve person and vice versa ? 

If a person is Rh negative, this means that they do not express the Rh protein on their red blood cells This protein is called the D protein. Rh+ cells do express this D protein. If one is exposed to Rh positive blood, either by transfusion with Rh+ red blood cells, these cells do express this D protein. The immune system recognizes this Rh protein on the transfused blood, and the immune system will respond to that blood as if it were any other foreign substance.
As far as the first time usually no significant ill effects is seen, since the transfused Rh+ cells only last several weeks anyway. If, however, the person is exposed to Rh+ blood again, the immune system mounts a strong and potent secondary immune response that can make you very ill (possibly life-threatening), mainly by destroying these 'invading' cells. Extravascular haemolysis more often occurs due to immune antibodies of the Rh system. The clinical manifestations are relatively less severe and usually consist of malaise and fever but shock and renal failure may rarely occur. Some patients develop delayed reactions in which the patient develops anaemia due to destruction of red cells about a week after transfusion. Such delayed reactions are generally the result of previous transfusion or pregnancy.