Immunology of human implantation: an evolutionary perspective.

The concept of the fetus as an allograft, which has been much cherished by reproductive immunologists, is in need of re-appraisal. We speculate that the relationship between the allogeneic conceptus and mother is not governed by the laws of classical transplantation immunity. Instead, this relationship is more akin to the allorecognition system seen in invertebrates.