Rat parathyroid allotransplantation: Influence of MHC antigen expression on graft survival

MHC antigen expression in parathyroid tissue and its influence on graft survival after allogeneic transplantation were investigated using a heterotopic rat transplantation model. MHC class I and II expression in parathyroid tissue of Lewis (LEW), Dark Agouti (DA), and Wistar-Furth (WF) rats was analysed semi-quantitatively by using immunohistochemistry. MHC class I expression was strong in DA, moderate in WF, and weak in LEW rats parenchyma, whereas MHC class II expression was negative. In the interstitium of all investigated tissue specimens, the proportion of MHC class II-expressing cells was low. Additionally, four groups were transplanted: 1) LEW to LEW, 2) DA to DA, 3) LEW to DA, and 4) WF to LEW. After syngeneic transplantation, graft survival could be documented over the whole observation period. A median graft survival of 20 (+/-2) days was observed after transplantation from LEW to DA, whereas grafts in the group WF to LEW were rejected after 13 (+/-1) days. The number of intra-graft leucocytes expressing MHC class II molecules was the same in all groups, whereas increased levels of MHC class I in parathyroid tissue before transplantation resulted in a more rapid rejection. These results indicate that immunogenicity of rat parathyroid tissue might be determined by the amount of MHC class I expressed in donor parenchymal cells. Further experiments are necessary to validate this observation.