Suppression of primary immunization to the rabbit red cell alloantigen HgA by passively administered anti-HgA.

Hg-negative rabbits were given an intravenous injection of Hg-positive red cells followed within 30 minutes by an intravenous injection of IgG anti-Hg. Several weeks later a second injection of Hg-positive red cells, without antibody, was given; the survival of these red cells was compared with the survival of red cells given to animals which had received no passive antibody. As judged by a relatively good survival of the second injection of red cells, primary immunization to Hg was at least partially suppressed when the dose of anti-Hg given with the first injection of red cells was such that 260–750 μg antibody was bound per m1 red cells. In three groups of animals given Hg-positive cells and anti-Hg in doses such that 20–40 μg antibody was bound per m1 red cells there was apparently no suppression of the antibody response. It is concluded that the amount of specific IgG antibody required for the suppression of primary immunization is at least ten times greater, in terms of μg antibody per m1 red cells, for the rabbit antigen Hg than for the human antigen Rh; the difference may be due partly to the greater number of Hg antigen sites on the rabbit red cell compared with the number of Rh(D) sites on the human red cell.