Problem:  To examine whether the NK1/NK2/NK3/NKr1 paradigm can be adapted in natural killer (NK) cells.

Method of study:  Mononuclear cells were isolated from peripheral blood and/or decidua in healthy non‐pregnant women (n = 17), early pregnant women (6–12 weeks of gestation, n = 17) and miscarriage cases (6–11 weeks of gestation, n = 10). We investigated the production of transforming growth factor (TGF)‐β, interleukin (IL)‐4, IL‐5, IL‐10, IL‐13, interferon (IFN)‐γ and tumor necrosis factor‐α from peripheral blood‐ and decidual‐CD56^bright NK cells and ‐CD56^dim NK cells by flow cytometry.

Results:  In the peripheral blood of the non‐pregnant subjects, the main populations of CD56^bright NK cells and CD56^dim NK cells were IFN‐γ‐producing NK1 type cells. Populations of IL‐10‐producing NKr1 type cells in peripheral blood CD56^bright NK cells and CD56^dim NK cells in early pregnant women were significantly greater compared with those in non‐pregnant women, and these cells population decreased in miscarriage cases. In the early pregnancy decidua, the main populations of CD56^bright NK cells and CD56^dim NK cells were TGF‐β‐producing NK3 type cells, and NK1 type cells were rare. NK3 type cells in decidua were significantly decreased in miscarriage cases compared with those in normal pregnant subjects. IL‐4‐, IL‐5‐ or IL‐13‐producing NK2 type cells were rare in peripheral blood and decidua.

Conclusion:  These data support the NK1/NK2/NK3/NKr1 hypothesis. NKr1 type cells in peripheral blood and NK3 type cells in decidua might play some important roles in the maintenance of pregnancy by regulation of maternal immune function.