Suppression of Primary Rh Immunization by Passively‐Administered Antibody. Experiments in Volunteers

Summary. Rh‐negative volunteers were given an injection of 1 ml of Rh‐positive red cells, either alone or with 15 μg or 75 μg anti‐D. Six months later anti‐Rh was detected in 2 out of 14 subjects who had originally received Rh‐positive red cells alone but in none out of 8 subjects who had also received 15μg anti‐D and in none out of 15 subjects who had also received 75μg anti‐D. Six months after the start of the experiment, thirty‐four of the subjects were injected with 1 ml of 51 Cr labelled red cells without anti‐D. At 7–11 days after injection, survival was normal in all of 13 subjects who had received 75μg anti‐D with their first injection of red cells. By contrast, survival was subnormal in seven out of 13 cases who had received no anti‐D with their first injection of red cells. This difference is significant (p = 0.027) and is taken to indicate that primary immunization occurred when 1 ml of Rh‐positive red cells was given alone but was prevented when 1 ml of red cells was given with 75μg anti‐D. Survival at 7 days was slightly subnormal in 2 out of 8 subjects who had received 15μg anti‐D with their first injection of red cells; this is taken as evidence that no augmentation of primary immunization was produced with this dose. In a follow‐up study of another series of Rh‐negative volunteers, who had been injected with 0.3 ml of Rh‐positive red cells at a Lime when they had between 0.6 arid 4μg anti‐D in their circulation, 3 to 8 months later the survival of injected Rh‐positive red cells was normal in 5 out of 6 cases, suggesting that there had been no augmentation of primary immunization.