Reaction of I-131 Trace Labeled Human Anti-Rh0(d) With Red Cells*†

nell, Coombs and Rizk (11) appreciated the pos- sibilities offered by the I-13 1 protein label and tagged human anti-Rho(D) serum. They were able to use the labeled isoantibody to estimate the number of Rho (D) sites and the Paul-Bunnell sites on the red cell, and more recently the anti- gen sites on the rabbit red cell (12). Melcher, Steinfeld and Reed (13), using both I-131 sheep red cell agglutinating rabbit serum and an I-131 incomplete red cell antibody, obtained from a patient with acquired hemolytic anemia, were able to show by zone electrophoresis that the red cell isoantibody activity was associated with the gamma globulin fraction.