Characterization of decidual leukocyte populations in cynomolgus and vervet monkeys

The objective of this study was the phenotypic and functional evaluation of decidual immune cells in the cynomolgus and vervet monkeys. Early pregnancy (days 36–42) deciduas were obtained by fetectomy for histological evaluation and decidual mononuclear leukocyte (MNL) isolation. While peripheral NK (pNK) cells in these species do not express CD56, CD56+ NK cells were abundant in decidual samples. The majority of decidual NK (dNK) cells (>80%) had high light-scatter characteristics and were CD56brightCD16+ cells with no or very low levels of natural cytotoxicity receptors (NKp46, NKp30) and NKG2A, while a minor population were small CD56dimCD16− lymphocytes also expressing less NKp46, NKp30 and NKG2A than pNK cells. All dNK cells were found to be perforin+; however, their cytotoxic potential was low and cynomolgus dNK cells showed strongly reduced cytotoxicity against target cells compared with pNK cells. Macrophages and T cells together comprised approximately 25–30% of decidual MNL. Decidual T cells contained a higher proportion of the minor T cell subtypes (γδT cells, CD56+ T cells) compared with peripheral blood. A subset of DC-SIGN+ macrophages, with a distribution adjacent to areas of placental attachment in contrast to the widespread setting of general CD68+ cells, was identified in both species. Together, these results demonstrate that the maternal–fetal interface in both cynomolgus and vervet monkeys is very rich in immune cells that have similar phenotypes to those seen in humans, indicating that both species are excellent models to study the contributions of distinct immune cell populations to pregnancy support.