Galectin-9/Tim-3-dependent mechanism of regulation of functional activity of natural killers during pregnancy

Galectins are a family of β-galactoside-binding low molecular weight proteins (lectins) homologous in the amino acid sequence of the carbohydrate-binding site. Galectins interact with glycans on the cell surface and are involved in regulating the functional activity of most cells of the human body. Galectin-9 plays a crucial role in controlling the functions of cells of the immune system. Of particular importance are the immunoregulatory effects of galectin-9 during pregnancy, when its production by trophoblast cells increases significantly, which is associated with the formation of peripheral immune tolerance. The main ligand for galectin-9 is the Tim-3 (T-cell immunoglobulin and mucin domain 3) molecule, whose high expression is detected on natural killers (NK cells). During pregnancy, the phenotype and functions of NK cells change significantly, which is necessary to prevent cytotoxic reactions to fetal cells. The review systematizes data on the role of galectin-9 in Tim-3-mediated regulation of NK cell functions in the aspect of pregnancy. The study of the regulation of the functional activity of NK cells is necessary to increase the effectiveness of NK cell therapy.