Role of Siglecs and their ligands in the establishment of immune tolerance at maternal-fetal interface
Embryo is regarded as a semi-allograft for carrying paternal genetic information. It can escape the attack from maternal immune system and successfully implant into the uterus, which mainly relies on the establishment of immune tolerance at the maternal-fetal interface. The maternal-fetal interface is the basis for the connection and material exchange between the mother and fetus. The mechanisms of immune responses at this interface are the key to the maintenance of normal pregnancy. Immunomodulatory molecules expressed at the maternal-fetal interface are vital for immune tolerance. Studies have shown that sialicacid-binding immunoglobulin-like lectins (Siglecs) are abundantly expressed at the maternal-fetal interface and play an important role in immune regulation. Siglecs are important members of the typeⅠimmunoglobulin-like superfamily. By binding with the sialic acid residues on the side chains of glycoproteins or glycolipids, Siglecs involve in immune regulation, the activation and proliferation of immune cells and immune cell-mediated physiological and pathological processes. Present research on the expression of Siglecs in the maternal-fetal interface is mainly focused on Siglec-6 and Siglec-10, while other Siglecs are less studied. Siglecs, such as Siglec-6 and Siglec-10, might involve in the regulation of immune tolerance at the maternal-fetal interface through binding to different ligands. This article briefly reviewed the expression of Siglecs and their ligands at the maternal-fetal interface and their roles in immune tolerance. 
 
 
Key words: 
Siglecs; Immune tolerance; Maternal-fetal interface