Galectin-9 influences the Tim-3 molecule expression in natural killer different subpopulations

Galectin-9 is a b-galactoside binding lectin with expressed immunoregulatory activity. During pregnancy galectin-9 is produced by trophoblast cells and regulates the function of natural killer (NK) cells at the maternal-fetal interface via binding to Tim-3 (T-cell Ig and mucin domain-containing protein 3) molecules. Natural killer (NK) lymphocytes belong to the innate lymphoid cells, which have a cytotoxic effect on target cells and are capable of producing a large number of regulatory factors (cytokines, chemokines). Decidual NK have a tolerant phenotype and play a leading role in the regulation of invasive trophoblast growth and provide peripheral immune tolerance in the area of uteroplacental contact. Peripheral NK cells express Tim-3 molecules. Galectin-9 concentration is increased in peripheral blood during physiologic pregnancy. At pregnancy phenotype and functions of peripheral NK cells are changed to maintain the maternal–fetal immune tolerance. Peripheral NK cells migrate to the maternal-fetal interface and are transformed into a decidual NK-like phenotype cells. Galectin-9 concentration is decreased in women with a  complicated  pregnancy and miscarriage. However the galectin-9 effects on different NK cell subpopulations of peripheral blood are not investigated. Therefore, we studied the galectin-9 influence on phenotype transformation and Tim-3 expression of NK cells isolated from peripheral blood of healthy non-pregnant fertile women. CD56+NK cells were obtained by immunomagnetic separation and cultivated in vitro during 72 hours with cytokines (IL-2 and IL-15). Galectin-9 (5 ng/mL) and anti-Tim-3 (10 mg) antibodies were added to the NK cultures. Galectin-9 concentration is corresponded to its level during first trimester of physiologic pregnancy. The number of regulatory NK (CD16-CD56bright), cytotoxic NK (CD16+CD56dim/-) cells and Tim-3 expression on different NK subpopulations were assessed by flow cytometry. It was found that Tim-3 was expressed on all subpopulations of peripheral blood NK cells (CD16-CD56brightNK, CD16+CD56dimNK, CD16+CD56-NK). Incubation with galectin-9 increased the expression of Tim-3 on regulatory CD16-CD56brightNK cells and did not change on cytotoxic CD16+CD56dim/-NK cells. Galectin-9 reduced the percentage of cytotoxic CD16+CD56dimNK in culture, but did not influence the number of regulatory CD16-CD56bright NK and cytotoxic CD16+CD56-NK cells. Thus, galectin-9 regulates Tim-3 molecule expression and NK cell subpopulation distributions in vitro culture.