Ethical hazards of the substituted judgement test in decision making concerning the end of life of dementia patients

Previously we reported that the South American gray short-tailed opossum, Monodelphis domestica, had an MHC class-I locus similar to that of eutherian species. In addition to the detection of lymphocyte antigens by cytotoxic antisera, we concluded that this marsupial rejected allogeneic skin grafts, as would be expected of animals with MHC class-I polymorphism. However, this conclusion was based on a limited number of skin transplants that were assayed for only a short period. Here we report the results of 22 reciprocal skin grafts made between individuals of known genetic relationships. On the basis of gross inspection of the grafts and histologic examination, we found that the average time of the onset of graft rejection was about 19 days and that the average time for complete graft rejection was about 31 days. In general, it took longer for the onset of graft rejection among pairs of genetically related animals than among less related animals. These results indicate unequivocally that this marsupial species has a high degree of class-I polymorphism and rejects allogeneic skin transplants in a manner similar to but more slowly than eutherian mammals.