Genital Tract and Circulating CD8+ T Cell Phenotypes Vary Across the Menstrual Cycle

Problem: The menstrual cycle consists of two main phases: the follicular phase, characterized by rising estradiol and low progesterone, and the luteal phase, marked by elevated progesterone following ovulation. Changes in sex hormones have profound physiological effects, yet their impact on immunity remains poorly understood. The prevailing theory suggests that reduced immunity during the luteal phase facilitates embryo implantation but also increases susceptibility to infections. Thus, defining the impact of the menstrual cycle on genital and systemic immunity is critical to understanding how immunity at different sites may be affected. Method of study: We examined phenotypic differences in T cells from ectocervical and vaginal tissue biopsies and blood samples collected from 58 women in the follicular phase and 20 women in the luteal phase using flow cytometry and measured seventy-one cytokines and chemokines from serum and cervicovaginal secretions.