Histological study of homografts showing delayed rejection following levan administration

The delaying effect of continued administration of levan on mouse skin homograft rejection was found to be due mainly to inhibition of thrombotic occlusion of the nutrient blood vessels. Levan administration did not appear to affect epidermal regeneration, but it seemed to inhibit degranulation of mast cells, resorption of plasma extravasated during the operation and growth of granulation tissue. The delayed rejection caused by levan treatment was apparently caused by infiltration of the graft by activated mononuclear cells from the blood stream. The phenomenon is believed to represent a late stage of the graft rejection process, its apperance depending on the survival of the graft beyond the stage of vascular occlusion.