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). gamma delta 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.