Figure 3.

Uterine immune stages during menstruation cycle. During the normal menstrual cycle, the human endometrium is exposed to cyclical fluctuations of sex hormones. The repetitive cycles of proliferation, differentiation, decidualization, and shedding of this tissue during mensuration and the steroid hormones per se cause profound changes in the immune cells' population. The estrogen-dominant proliferative phase is characterized by the regeneration of the functional layer of the endometrium. In the progesterone driven secretory phase, the endometrium undergoes a number of changes in preparation for implantation of the embryo. The immune cells that undergo greater number variations in the secretory phase are the NKs and macrophages. The microbiota, on the other hand, does not undergo large variations during different phases of the menstrual cycle. Sphingobium sp., Propionibacterium acnes, and Pseudomonas sp. are differentially enriched during the proliferative and secretory phases; P. acnes is more abundant in the secretory phase and has previously been identified in the placenta and cultured from follicular fluid. Functionally, the proliferative phase, compared to the secretory phase, appears associated with increased bacterial proliferation. + + ++/+ represent the relative abundance amount of microorganisms.