Menstrual Cycle Dependent Fluctuations in NK and T-Lymphocyte Subsets from Non-Pregnant Human Endometrium

PROBLEM: To establish the relative proportions of endometrial lymphocyte subpopulations during the menstrual cycle. METHOD OF STUDY: 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. RESULTS: 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 natrual T cells (NT) CD3+CD56+, increased significantly in the LS phase (P=0.05; P=0.03). ΓΔ T cells, predominantly of the DN and NT phenotypes remained consistently low at all stages of the cycle (2.34%). CONCLUSION: Endometrial lymphocyte fluctuations during the menstrual cycle may reflect hormonal regulation of maternal immunity, thereby promoting tolerance at the time of implantation.