PREVENTION OF ALLOGENEIC FETAL REJECTION BY TRYPTOPHAN CATABOLISM

In 1953 Medawar pointed out that survival of the genetically disparate (allogeneic) mammalian conceptus contradicts the Laws of tissue trans plantation. Rapid T cell-induced rejection of all allogeneic concepti occurred when pregnant mice were treated with a pharmacologic inhibito r of indoleamine 2,3-dioxygenase (IDO), a tryptophan-catabolizing enzy me expressed by trophoblasts and macrophages. Thus, by catabolizing tr yptophan, the mammalian conceptus suppresses T cell activity and defen ds itself against rejection.