A new form of polyagglutination related to Cad

Four phenotypes of Cad (Cad 1–4) have been characterized by a continuum of polyagglutinability and reactivity with lectins, with the strongest Cad+ red blood cells (RBCs) being polyagglutinable because of the presence of anti-Cad (anti-sd^a) in most normal sera. Over a period of 7 years, a French male blood donor’s RBCs demonstrated polyagglutinability with 50 percent to 70 percent of normal adult sera. The reactivity was characteristic of anti-sd^a (refractile agglutination at 4°C, 20°C, 37°C, and anti-human globulin test), and was inhibitable by two examples of Sd(a+) urine, but not by Sd(a–) urine or dialysate from Sd(a+) urine. The donor’s RBCs reacted 1+ with Glycine max, but did not react with Dolichos biflorus, Leonurus cardiaca, Salvia horminum, or Arachis hypogaea. The first four of these lectins were reactive with five of five Cad+ RBCs, including one example of Cad 4 RBCs. Polybrene® aggregated the donor RBCs. Dilutions of nine samples of anti-Sd^a reacted more strongly with the donor RBCs than with normal RBCs. Even though lectin studies failed to classify this donor’s RBCs as Cad, the persistent polyagglutinability and serologic characteristics are consistent with Cad and demonstrate the heterogeneity of this antigen. Immunohematology 1996;12:69–71.