B Scientists may have found a way to reduce shortage of type O blood. Type O is the kind of blood that hospitals most often need. What the researchers are testing is an easier way to make type O blood out of other kinds of blood. There are four main kinds of blood. Most people born with one of these four: Type A, Type B, Type AB or Type O. Type O can be safely given to anyone. So it is commonly used when a person is injured or sick and has to have blood. Type O is the most common blood group. But the supplies of it available in hospitals and blood banks are usually limited. This is because of the high demand for it. Type O blood is used in emergencies when there is no time to identify the patient’s blood type. Giving A,B or AB to someone with a different blood type, including O, can cause a bad reaction by the person’s defense system. Their immune system can reject the blood. This immune reaction can be deadly. The differences among blood types are linked to whether or not red blood cells contain certain kinds of sugar molecules. These molecules are found on the surface of the cells. They are known as antigens( 抗原 ). These antigens are found with type A, B and AB bl ood but not with type O. More than twenty-five years ago, scientists found that the antigens could be removed to create what they called universal-type cells. They could be removed with chemicals called enzymes( 酶 ). But large amounts of enzymes were required to make the change. Doctor Henrik Clausen of the University of Copenhagen in Denmark led the study. The next step, he says, is to complete safety tests. The team is working with the American company ZymeQuest to test the new method. If it meets safety requirements( 要求 ) and is not too costly, it could become a widely used life-saving tool to increase the supply of universal blood.