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