RELATIONSHIP BETWEEN Rh0(D) GENOTYPE AND QUANTITY OF I131 ANTI-Rh0(D) BOUND TO RED CELLS*

Abstract

An estimate of the Rho(D) antigen content of 199 different Caucasian red cells was obtained from the quantity of I131 trace labelled incomplete anti-Rho(D) bound to the red cells. The validity of the technique was evaluated by defining the experimental errors, the Rho(D) specificity of the I131 anti-Rho(D), and the quantitative relationship between volume of red cells, quantity of I131 anti-RhoD) bound to the red cells, and the I131 anti-Rho(D) that could be demonstrated in the supernate. The quantity of I131 anti-Rho(D) bound to rh[image](C) negative, Rho(D) positive red cells showed a bimodal distribution. The group of cells with the higher antigen content (1.6 times) was identified with the homozygous state [Rho(D), Rho(D)] and the other group with the heterozygous state [Rho(D), rh(d)], by using genetically defined heterozygous Rho(D) red cells obtained from family studies. The rh[image](C) positive red cells took up only 70 to 73% of the I131 anti-Rho(D) that was bound to the rh[image](C) negative cells. The decrease in quantity of bound I131 anti-Rho(D) was uniform for both Rho(D) genotypes, except for the cells homozygous for the rh[image](C) antigen. This effect of the rh[image](C) antigen of the Rho(D) content may be apparent (immunochemical basis) or absolute (genetic mechanism). Evidence for the heterogeneity of the Rho(D) antigen was obtained. As a result, the data presented apply only to the Rho(D) antigen defined by the particular I131 anti-Rho(D) used in this study.