AbstractPresentation of alloantigens by host cells has been examined in vivo by means of a murine cell transfer system. Primary (1°) hosts were activated by the i.p. administration of allogeneic spleen cells and their spleen or peritoneal cells were transferred into syngeneic secondary (2°) hosts 3 days later. Sensitization of 2° hosts was assessed by their ability to reject donor strain skin grafts prematurely. The transferred cells were routinely depleted of T lymphocytes. We show that (a) 5 × 107 spleen and 3 × 106 peritoneal cells consistently caused marked accelerated graft rejection; (b) this effect was antigen specific and observable in all strain combinations studied; (c) it was caused by the active sensitization of 2° hosts, but not by contaminating donor strain cells; (d) the cells involved were plastic adherent and viability was not a requirement; and (e) both class I and II, but not minor, histocompatibility antigens played a role in this model. We conclude that presentation of alloantigens by host antigen‐presenting cells can be a potent route of allosensitization.
