Tolerance Signaling Molecules and Pregnancy: IDO, Galectins, and the Renaissance of Regulatory T Cells

Abstract

Problem Is the concept of maternal tolerance preventing rejection of the semi‐allogeneic ‘fetal allograft’ still valid? Method of study Compilation of expert reviews of literature and recent advances in research on indoleamine‐2,3 dioxygenase (IDO), regulatory T cells and galectin‐1. Results and Conclusion A role for IDO in pregnancy success remains speculative, but solid data exist to support a role for Treg cells, and for galectin‐1 in induction and action of Treg cells. Just as several signals may need to be simultaneously present to induce Th1 cytokine‐triggered abortions, more than 1 signal may need to be simultaneously present to prevent rejection and ensure success. Both complement and coagulation pathways appear necessary for embryo execution.