Skin graft rejection after allogeneic tooth transplants in mice

Three strain combinations of in-bred mice representing strong and moderate histocompatibility barriers were used to determine if tooth allotransplants evoked strong or weak immunologic memory as measured by the second-set donor-strain skin graft technique. At issue was whether the anatomic site of engraftment could influence the outcome of these experiments. Recipients received either 5-mm-diameter skin grafts or one or four adult teeth. Experimental transplants were placed in subcutaneous pouches or in ear pouches. Control mice received only orthotopic skin grafts. Second-set orthotopic skin grafts were placed either one mo, six mo, or 11 mo after primary transplants. Skin grafts were observed daily until rejection occurred. We found that skin provoked strong memory in subcutaneous tissues, but that teeth generated very weak memory in subcutaneous tissues. Conversely, teeth placed in ear pouches were able to generate strong immunologic memory. This occurred whether donor and recipient shared H-2 allo-antigens, or whether one tooth or four teeth were grafted, and the difference persisted for at least six mo. We conclude that teeth are not weak antigens, nor is the subcutaneous site privileged regarding immunologic memory. Rather, there seems to be some critical interaction between teeth and the immune system draining subcutaneous tissues that results in a failure to generate strong anamnestic immunity. Perhaps definition of the processes involved will be of advantage in future human applications.