Menstrual cycle dependent fluctuations in NK and T-lymphocyte subsets from non-pregnant human endometrium

To establish the relative proportions of endometrial lymphocyte subpopulations during the menstrual cycle.

Lymphocytes were investigated by flow cytometry, during the early proliferative (EP), late proliferative (LP), early secretory (ES) and late secretory (LS) phases of the menstrual cycle.

Between the LP and LS phases, there was an increase in NK cells from 26.4% to 83.2% (P = 0.0017) of the CD45+ population. T cells decreased from 55.06% to 6.7% (P = 0.0017). Within the T-cell population, CD8+ cells decreased significantly from 63.0% in the LP phase to 54.2% in the LS phase (P = 0.04). In contrast, potential regulatory populations such as double negative (DN) T cells CD3+CD4-CD8- and natural T cells (NT) CD3+CD56+, increased significantly in the LS phase (P = 0.05; P = 0.03). gammadelta T cells, predominantly of the DN and NT phenotypes remained consistently low at all stages of the cycle (2.34%).

Endometrial lymphocyte fluctuations during the menstrual cycle may reflect hormonal regulation of maternal immunity, thereby promoting tolerance at the time of implantation.