Quantitative comparison of Rh1 (Rho, D) antigen on D, Du and d red cells by radioimmunoassay using 125I-protein A.

Relative Rh1 (Rho, D) antigen contents of the red Rh: 1 (Rh positive, D), Rh: wl (Rh variant, Du) and Rh: -1 (Rh negative, d) cells were estimated from the quantity of 125I-protein A bound to the sensitized red cells. The isotope binding activity to both D and Du cells decreased in parallel with the dilution of anti-D serum. The relative amount of the 125I-protein A bound to Du cells was about one-sixth that of D cells without papain treatment, while no isotope binding was observed in d cells. The Du red cells were quantitatively deficient in Rh1 (Rho, D) antigen activity compared with the D cells. A radioimmunoassay using 125I-protein A was a very useful method for studies regarding measuring the relative amounts of various blood group antigens.