• Endometrium;
  • flow cytometry;
  • natural killer cell;
  • peripheral blood


Cyclic changes of peripheral natural killer (pNK) cells and/or endometrial NK (eNK) cells during menstrual cycle remain controversial, and their relationship remains uncertain.

Method of study

Peripheral blood and endometrial biopsies were simultaneously obtained from women (n = 23) undergoing artificial insemination with donor sperm (AID) for at least three cycles at both proliferative (days 9–11) and secretory phases (days 20–23) of menstrual cycle. The percentages of CD3− CD56+, CD3− CD56dim CD16+, CD3− CD56bright CD16 pNK, and eNK cell subsets within lymphocytes were determined by three-color flow cytometry. The correlation between the percentages of pNK and eNK cells was further analyzed by Spearman's test.


The percentages of CD3− CD56+, CD3− CD56dim CD16+, and CD3− CD56bright CD16 pNK cells were not statistically different between the proliferative and secretory phases (> 0.05, respectively). However, the percentages of CD3− CD56+ and CD3− CD56bright CD16 eNK cells were significantly decreased at the secretory phase, compared with those in the proliferative phase (< 0.05, respectively). No correlation between the percentages of all pNK cell parameters and those of CD3− CD56bright CD16 eNK cells (the major subset of NK cells in uterus) was found in the same women throughout the menstrual cycle (> 0.05).


We found a menstrual-cycle-dependent change in the percentage of eNK cells in women undergoing AID treatment, but not pNK cells. Moreover, the percentage of pNK cells may not reflect that of eNK cells during menstrual cycle.