Immunogenicity of Parathyroid Allografts in the Rat: Immunosuppressive Dosages Effective in Passenger Leukocyte-rich Small Bowel Transplants Are Not Effective in Parathyroid Gland Transplants with Few Passenger Leukocytes

Background And Aims: The passenger leukocytes harboured within an allograft induce a massive allo-immune response that leads to allograft rejection if not countered by immunosuppression. We compared the response to short-term immunosuppression of parathyroid gland transplants possessing few passenger leukocytes with that of passenger leukocyte-rich small bowel transplants.

Methods: Heterotopic parathyroid and orthotopic small bowel transplantation was performed in a Wistar Furth-to-Lewis rat strain combination. Immunosuppression with cyclosporine A (CsA) was administered in different dosages for 14 days. Dysfunctional allografts were examined immunohistologically.

Results: CsA more effectively suppressed the immune response provoked by immunogenic small bowel grafts than that induced by less-immunogenic parathyroid grafts. Immunosuppression with 20 mg/kg per day induced long-term survival in the small bowel (165+/-21 days) but not in the parathyroid (28+/-3 days). All rejected grafts featured massive cellular infiltration by activated T cells as a sign of immune rejection.

Conclusion: Immunosuppressive dosages effective in passenger leukocyte-rich small bowel transplants were not as effective in parathyroid gland transplants harbouring few passenger leukocytes. In spite of the paucity of passenger leukocytes in parathyroid grafts it is more difficult to control by immunosuppression the immune response to them than that to the passenger leukocyte-rich small bowel.