Figure 1.

(A) The concentration of estrogen (green) and progesterone (red) fluctuates during the phases of the menstrual cycle and is associated with morphological changes in the cellular components of the mammary gland; shown here in carmine alum-stained mouse mammary gland whole-mount preparations (B) [adapted from Ref. (17) with permission]. (C) The follicular phase of the menstrual cycle is characterized by increase in the number of Tregs and proteoglycans compared to the luteal phase. In contrast, the luteal phase is characterized by increased numbers of mammary epithelial cells as well as increased abundance of macrophages compared to the follicular phase. The phenotype of macrophages in the mammary gland also changes throughout the cycle.