Tryptophan catabolism prevents maternal T cells from activating lethal anti-fetal immune responses

The murine conceptus is protected from maternal immunity by cells expressin g indoleamine dioxygenase (IDO), which catabolizes tryptophan. Induction of lethal maternal anti-fetal immunity requires effective pharmacologic inhib ition of IDO enzyme activity and the presence of maternal T cells, but not B cells and also depends on the degree of maternal-fetal tissue incompatibi lity. Based on these findings, we propose a model to explain the role of ID O in suppressing maternal immunity and the mechanism of fetal allograft rej ection, when IDO activity is inhibited during gestation. This model incorpo rates observations that fetal allograft rejection is T cell dependent, anti body-independent and is accompanied by a novel type of inflammation involvi ng extensive complement deposition at the maternal-fetal interface, when ID O activity is blocked during murine pregnancy. (C) 2001 Elsevier Science Ir eland Ltd. All rights reserved.