Cad(super Sda) in a British family with eastern connections: a note on the specificity of the Dolichos biflorus lectin.

Cad, Sd(a++) or Super Sda is a rare, inherited, dominant blood group character which is of much interest, not only with regard to problems in pretransfusion tests (erythrocyte polyagglutination) but also in the field of lectin specificity. We have studied this blood group character in a British family with Eastern connections and present a brief account of its serological and clinical importance. Most persons are Sd(a+) but there is a wide distribution of antigen strength, ranging from ordinary Sd(a+) to Cad. Most persons also have weak anti-Sda in their serum; this is ordinarily of no clinical importance, but could cause problems if Cad bloods are transfused. The chief structural determinant of Cad specificity is N-acetyl-D-galactosamine in alpha-linked position, yet it is clearly distinguishable by use of appropriate lectins from other blood group antigens, A and Tn, which also have this acetyl-hexosamine as their chief structural determinant. A method for the rapid identification of Cad, applicable to all ABO groups, is described. The lectin of Dolichos biflorus, which is specific for N-acetyl-D-galactosamine in alpha-linked position, reacts strongly with A(A1), Tn and Cad cells, its action on Cad cells being much the strongest. Absorption-elution studies show that one and the same lectin reacts with both A1 and Tn cells. Absorption with Cad cells abolishes activity for A1, Tn and Cad cells; whereas absorption with A1 or Tn cells leaves activity for Cad. This does not necessarily indicate that anti-Cad is a separate component since the same result can be obtained by simply diluting the Dolichos reagent. However, eluates from Cad cells react only with Cad cells, whereas eluates from A1 or Tn cells react with A1, Tn and Cad cells.