The Immunoregulatory Function of Indoleamine 2, 3 Dioxygenase and Its Application in Allotransplantation

Indolemine 2, :,)-dioxygenase (ido) is a cytosolic monomeric hemoprotein enzyme thatcatalyses tryptophan, the least available essential amino acid in the human body, to nformylkynurenine,which in turn rapidly degrades to give kynurenine. ido is expressed indifferent tissues, especially and prominently in some subsets of antigen presenting cells(apes) of lymphoid organs and also in the placenta of human and other mammals.expression of ido by certain dendritic cells, monocvtes and macrophages has a regulatoryeffect on t cells probably by providing a tryptophan-deficient microenvironment and/oraccumulation of toxic metabolites of tryptophan. this immunomodulatory function of idoplays an essential role in different physiological and pathological states, ido was shown toprevent rejection of the fetus during pregnancy, possibly by inhibiting alloreactive t cells.moreover, ido expression in apes was suggested to control autoreactive immuneresponses. in this review we discuss the molecular and biological characteristics of ido andits function in immune system as well as the potential application of this enzyme inimproving the outcome of allogeneic transplantation as a local immunosuppressive factor.