Induction of specific immunological tolerance of homografts in adult mice by sublethal irradiation and injection of donor-type spleen cells in high dosage

Abstract

Adult A-strain mice in the weight-range 15 to 20 g were irradiated to 350 or 500 r, followed by the injection, divided between the intravenous and intraperitoneal routes, of suspensions of spleen cells obtained from CBA or (CBA x A) F1 mice, donors and recipients being matched for sex. After the lapse of 18 to 25 days all mice, including control batches which had received irradiation but not spleen cells, were challenged with donor-type skin grafts. Mice irradiated to 500 r which received CBA spleen cells in doses from 500 to 1500 million developed severe graft-versus-host disease, fatal in most cases. Rejection of the grafts occurred in irradiated controls after periods ranging from 8 to 23 days. Mice receiving 500 r followed by (CBA x A) F1 spleen cells showed prolonged survival of skin grafts, amounting to 90 days or more in animals which had received the highest dose of cells (12 x 109). Analysis of the phenomenon by means of Simonsen''s discriminant spleen assay showed that approximately 85% of the immunologically competent spleen cells of the graft-bearing animals were replaced by cells of donor origin; the remainder, however, retained the power to react immunologically against third-party (C57BL) antigens. It was also possible to secure adoptive rejection of grafts by injection of 60 to 90 million A-strain lymph node cells pre -sensitized against CBA. It is concluded that the state of specific unresponsiveness induced in the adult A strain mice represented a specific central inhibition of the mechanism of immunological response and could thus be equated to immunological tolerance as classically defined. Prior splenectomy not only abolished the tolerance phenomenon, but actually reversed it, there being clear signs of an immunity resulting from the irradiation and injection procedure. This result is discussed in terms of the significance of antigen dose-level for the induction of tolerance.