Abrogation of immune tolerance to protein antigens in tolerant rabbits and mice by transfer of allogeneic spleen cells in small doses

When small doses of allogeneic spleen cells are injected into rabbits or mice made tolerant to either human or bovine serum albumin, about half the treated animals will escape from tolerance. The effective doses in rabbits are 2 x 10⁶ to 5 x 10⁶ cells per animal and in mice 10⁴ to 10⁶ cells per animal. Larger doses, around 25 x 10⁶ cells in rabbits, are ineffective. It is suggested that by transferring sufficiently small doses of allogeneic cells the threshold of the recipient's rejection mechanism can be circumvented.