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[Role of natural killer cells in normal pregnancy and recurrent pregnancy loss].

Pregnancy is an immunological mystery. The conceptus survives and develops despite being an allogenic transplant, in terms of classical immunology. Natural killer cells are the predominant immune-cell population in the early human placenta. The role of these cells in human pregnancy is not fully established, yet it presumed they are required for placental development and local immunomodulation at the maternal-fetal interface. The purpose of this review is to examine recent progress in characterizing natural killer cells, the quantitative and qualitative changes that occur in these cells through pregnancy. We will also point out the possible role of these cells in the maintenance of normal pregnancy and the pathogenesis of recurrent pregnancy loss.