Quantitative Serologic and Isotopic Studies on the Rh_o Variant—D^u

1. Type D^u cells take up less than 10 per cent of the I-131 anti-D bound to D positive cells, so that the quantity of cell bound I-131 did not differ significantly from that bound nonspecifically to D negative cells.

2. Papain modification of D^u cells results in an almost threefold increase in the uptake of I-131 anti-D, whereas, D negative cells show no consistent increase after such treatment. Enzyme modification, therefore, serves to clearly delineate the two cell types.

3. The range of uptake of I-131 anti-D to enzyme treated D^u cells is from approximately 7 to 17 per cent of that by R₁R₂ cells. Most of these results were obtained from studies on Mendelian D^u types. Studies on several bloods from members of a family having Rh genotypes typical of the "gene interaction" D^u configuration (C in transposition to D) revealed no significant reduction in I-131 anti-D uptake when compared with D positive cells.

4. Decreased antibody binding to D^u cells was confirmed by the serologic methods used. Absorption of an anti-D serum and antiglobulin inhibition with sensitized D^u cells indicated that the quantity of D antigen was less than that observed with the isotopic technic. Elution studies did not show as marked a reduction of D antigen on the D^u cell as the other serologic technics indicated. Possible reasons for these differences have been discussed.

5. Although, from both the serologic and isotopic studies, the data indicate that the type D^u red cell is quantitatively deficient in D antigen, they are inadequate to rule out other explanations for their reduced D antigen activity. Irrespective of the mechanism(s) responsible, the effective binding of anti-D by D^u cells is reduced several fold; this would appear to be the primary cause of the weak second stage of red cell antigen-antibody reaction which characterizes type D^u blood.