A volunteer called a(n) donor can give blood. The recipient is the person who receives the blood. When the first transfusions were performed last century, the patient sometimes died. A and B antigens were discovered on the surface of red blood cells. People without these antigens have type O blood. Certain antibodies or proteins in blood help the body destroy harmful materials. Rh negative blood forms clumps around Rh positive blood. When mothers and babies have different blood types, doctors use special medicines.