Amniotic fluid glycoproteins as potential ligands for macrophage galactose-type C-type lectin and their possible implications for immunoregulation during pregnancy

Immunity during pregnancy must be precisely balanced, because the mother's body needs to effectively fight pathogens while maintaining tolerance of the semi-allogeneic fetus. Factors that participate in achieving the proper immune balance during pregnancy include glycoproteins that expose sugar residues recognized by specific lectin receptors. Several types of lectins and their ligands have been detected at the maternal-fetal interface, and changes in their expression levels have been correlated with pregnancy complications. Although the presence of potential sugar ligands for human macrophage galactose-type lectin (MGL), including LacdiNAc and (sialo)Tn antigen, has been detected in amniotic fluid, placenta and fetal tissues, the interaction between them and its possible role have not been elucidated so far. The aims of the present study were to evaluate reactivity of MGL with amniotic fluid proteins and to identify and characterize the amniotic ligands of MGL. The analysis proved the ability of MGL to interact with amniotic glycoproteins and revealed the potential protein carriers of glycans recognized by MGL, including mucins, mucin-like proteins, and uromodulin. Bioinformatics analysis assigned the identified glycoproteins as being involved in immune processes such as regulation of signaling pathways activated in the response to Toll-like receptor (TLR) agonist stimulation or modulation of antimicrobial responses. Our research suggests that MGL-mediated interactions may be involved in maintaining the delicate immune balance during pregnancy. Our results may be helpful in future implementation of modern therapies based on the glycan ligands of MGL in the context of avoiding miscarriages and preterm birth.