Quantitative Studies of the Rh o (D) Antigenic Determinants on Gorilla Erythrocytes

Human and simian red blood cells were tested for 125 I anti‐D binding at equilibrium and for their ability to adsorb 125 I anti‐D. On the basis of the equilibrium quantity of red blood cell‐bound anti‐D at different ionic strengths, the rate of binding of anti‐D, and adsorption studies, evidence has been obtained that D‐antigenic specificities occur on the erythrocytes of orangutans ( Pongo pygmaeus ), chimpanzees ( Pan troglocytes ) and gorillas ( Gorilla gorilla ). Gorillas, like chimpanzees, appear to be polymorphic with respect to the presence of D‐components on their erythrocytes. Individual animals have been found whose red blood cells take up very little anti‐D and are similar to human D‐negative cells. The quantity of anti‐D bound at equilibrium, as a fraction of that bound to human D‐positive red blood cells was: for gorillas 0.6 to 4.0; for chimpanzees 0.08 to 0.51; for orangutans 0.06 to 0.09, and for human D u red blood cells 0.04. At low ionic strength there was almost a twofold increase in anti‐D binding. At low ionic strength, the adsorbing capacities of these erythrocytes, as compared to a human D‐positive cell, were: orangutans 10 to 20 per cent; chimpanzees about 50 per cent; human D u 86 per cent; and gorillas 97 per cent. Evidence is presented to indicate that the discrepancy between adsorbing capacity and the binding of anti‐D at equilibrium, for D u and simian erythrocytes, is due to absence of some of the D‐antigenic components found on human D‐positive red blood cells.