Heart and spleen "twin grafts" in rats: IV. Influence of donor spleen cell mass on allograft survival

Heart and spleen twin grafts from LEW to ACI rats may survive permanently, whereas those grafted from ACI to LEW rats do not. This strain difference in graft acceptance was analyzed quantitatively by transplanting one to three ACI spleens into LEW rats in order to compensate for the relatively small size of ACI spleens (Fig. 1). Under these conditions permanent graft survival was not observed in LEW recipients. However, during host splenectomy 3 days after transplantation, a nonimmunological factor was observed. The transplanted ACI spleens showed congestion and infarctions, while in the LEW to ACI transplant model the LEW spleens did not. This observation could be explained by the size of the vascular pedicle in ACI spleens. Although no problem was encountered immediately after completing the anastomoses, allogeneic spleens react by increasing in size, to such an extent that their size exceeds the capacity of the smaller vascular pedicle in ACI rats and results in congestion. Hence, the concept is formulated that early compromise of hemodynamics on a nonimmunological base may determine the fate of ACI spleen graft before immunological factors have a chance to become effective.