Cyclic Changes in the Concentrations of Peripheral Blood Immune Cells During the Normal Menstrual Cycle

Abstract

Abstract

The optimal availability of immune cells in the peripheral blood streams of women may play a critical role in their response to disease and therapeutic interventions. This study was designed to examine concentrations of circulating white blood cells (WBC) including lymphocyte subsets, during the 24-hr daily and 28-day menstrual cycles. Venous blood (20 ml) from five healthy young women was obtained at 0, 6, 12, and 18 hr on the 6th and 22nd day of the normal menstrual cycle. Cortisol, progesterone (P4), estradiol (E2), total WBC, granulocyte, monocyte, and total lymphocyte levels were measured. Using fluorescent activated cell scanning, levels of T, B, Helper (H), Suppressor (S) and Natural Killer (NK) cells were also determined. Significant differences in the diurnal and Day 6 and 22 means were identified using analysis of variance and the Student's t test.

Mean WBC counts differed significantly between individuals and ranged from 3.63 ± 0.33 to 8.60 ± 1.00 on Day 6 and 3.75 ± 0.56 to 9.45 ± 0.98 on Day 22 (P < 0.05). Fluctuations in the concentrations of peripheral blood immune cells followed a similar pattern for the time points selected. They were lowest in the morning at 6 hr and reached peak concentrations in the evening at 17 hr or at midnight at 24:00 hr. Total WBC and granulocyte levels were consistently highest in the evening at 18 hr while lymphocyte levels either peaked in the evening or at midnight. Between midnight and early morning, levels of WBC, lymphocytes, T, B, H, and S cells all decreased significantly (P < 0.01) and subsequently increased significantly, between 6 hr and noon or noon and 18 hr(P < 0.01). When compared every 12 hr, the levels of WBC, granulocytes, lymphocytes, T, B, H, and S cells showed a significant day time rise between 6 and 18 hr (P < 0.02). NK cells revealed no significant fluctuations for any of the diurnal time point comparisons examined in this study.

The WBC means for all subjects on Day 6 was 6.15 ± 1.96 and on Day 22 was 6.39 ± 2.14, evidence that the total number of white blood cells was not significantly altered between the 2 days. However when comparing specific time points during the day for the follicular (Day 6) and luteal (Day 22) phases of the menstrual cycle, significant differences were found. Most striking were the monocyte patterns, which revealed a nadir at 12:00 noon on Day 6 and a peak at the same time on Day 22. WBC, and granulocyte levels were significantly higher at 12:00 noon on Day 22 (P < 0.05) and NK cells significantly lower on Day 6 at 18 hr (P < 0.01). Thus, within this population of normal menstruating women, quantitative and qualitative differences in the circadian and circalunar levels of peripheral blood immune cells do exist.