Although plant hemagglutinins, which have been known nearly as long as specific immune agglutinins, were long thought to be nonspecific, some have been found to have a blood-group specificity which is quite sharp. Some of these agglutinins, such as the lectins of Dolichos biflorus and Ulex europeus , have found important practical applications in blood group techniques. Other group specificities have been found, and even some of the plant extracts which agglutinate all human erythrocytes probably have a measure of specificity, since they are specificially inhibited by certain carbohydrates. The information that may be gained in this way concerning reactive structures in the red cell is discussed. A study of such reactions led M?kel? to classify all aldopyranoses into four groups, depending on their configuration at carbon atoms 3 and 4. The inhibition reactions of human anti-Rh sera suggest that this classification may be of significance in this connection also.
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