Objective:To investigate the distribution and regulation of uterine NK cells in mouse uterus during early pregnancy. Methods:Using a unique uNK cell marker

Dolichos biflorus agglutinin (DBA) lectin

to localize NK cells in uterus of normal pregnancy

delayed implantation and artificially induced decidualization. Results:DBA staining is mainly distributed in some vascular endothelial cells during embryo pre-implantation. In D5 of pregnancy after embryo implantation

NK cells were distributed in the stroma of uterine mesometrial pole

with round

immature and small lymphocyte-like cells. During D7 and D8 of pregnancy

the immunostaining results showed that uNK cells were increasingly accumulated in the mesometrial pole of implantation sites

with their morphology changing from small round cells with scattered cytoplasm to large and mature cells with heavy cytoplasmic granules. In the artificially induced decidualization model

the distribution and maturity of NK cells are similar to those of the normal pregnancy in the mouse uteri. Conclusion:The distribution and maturation of uterine NK cells are dependent of uterine decidualization in mouse early pregnancy.