Galectins are glycan-binding proteins that regulate innate and adaptive immune responses, and some confer maternal-fetal immune tolerance in eutherian mammals.  Three of the five human cluster galectins are solely expressed in the placenta, where they may confer additional immunoregulatory functions to enable deep placentation (PMID: 25191322). One of these is galactoside-binding soluble lectin 13 (LGALS13, also known as Galectin-13 and PP13), which has a high affinity for the sugar residues of glycoproteins. PP13 is implicated in placentation and is involved in inflammation and immune defense required for trophoblast invasion during uterine artery remodeling in early pregnancy (PMID: 19497882; 10527825; 21596368; 26018511).