Effect of Indoleamine 2,3-Dioxygenase Expressed in HTR-8/SVneo Cells on Decidual NK Cell Cytotoxicity

To study the effect of indoleamine 2,3-dioxygenase (IDO) expressed in HTR-8/SVneo cells on NKG2D and NKp46 expression and cytotoxicity of decidual NK (dNK) and peripheral NK (pNK) cells.CD56(+) dNK and pNK cells purified were cultured with HTR-8/SVneo cell conditioned medium (CM), 1-MT+HTR-8/SVneo cell CM, and complete RPMI 1640 medium (negative control) in vitro. The mRNA and protein expression of NKG2D and NKp46 in NK cells were then assessed by qRT-PCR and flow cytometry, respectively. Their cytotoxicity was evaluated with LDH assays, and TNF-α secretion was analyzed by ELISA.For dNK cells, the mRNA and protein expression of NKp46 as well as NKG2D did not differ significantly among the three groups (P0.05), whereas for pNK cells, the expression level was significantly decreased in HTR-8/SVneo cell CM group than the other two groups (P0.01). Peripheral NK cells cultured with HTR-8/SVneo cell CM showed reduced cytotoxicity and TNF-α secretion than the other two groups (P0.01), although there were no significant differences among three groups for dNK cells (P0.05).IDO expressed by HTR-8/SVneo cells can down-regulate NKp46 and NKG2D expression and reduce cytotoxicity in pNK cells, and may contribute to keep dNK cytotoxicity at a low level, suggesting an important role for IDO in the maintenance of normal pregnancy.