ROLE OF FAS-FAS LIGAND INTERACTIONS IN THE IMMUNOREJECTION OF ALLOGENEIC MOUSE CORNEAL TRANSPLANTS1

Background. The expression of Fas ligand (FasL) in the eye has been proposed to be an important component of ocular immune privilege. Since the unusually favorable outcome of corneal transplantation is thought to result from the immune privilege of the eye, examination of the function of FasL on corneal allografts would be a test of that hypothesis. Methods. To investigate the role of Fas-FasL interaction in corneal allografts, orthotopic corneal transplantation was performed using C57BL/6 (B6, FasL + ) and B6-gld (FasL - ) mice as cornea donors and BALB/c mice as recipients. The rejection rate of B6-gld grafts (FasL - group) was compared with that of normal B6 control corneas. Results. The rejection rate at the final observation (8 weeks) in the FasL - group (89%) was significantly higher than in the FasL + control group (47%). FasL expression was found on the corneal endothelium by staining with anti-FasL monoclonal antibodies. The TdT-mediated dUTP nick-end labeling assay revealed that apoptotic cells were attached to the endothelium in the control group but not in the FasL - groups. Conclusions. Apoptosis of infiltrating cells on the corneal endothelium resulting from Fas-FasL interaction plays an important role in the high success rate of corneal transplantation.