Oral Presentation The Annual Scientific Meeting of the Endocrine Society of Australia and the Society for Reproductive Biology 2014

Hormonal regulation of the immune microenvironment in the mammary gland: implications for breast cancer susceptibility (#124)

Wendy Ingman 1 2 3
  1. University of Adelaide, Woodville, SA, Australia
  2. Research Centre for Reproductive Health, Robinson Institute, Adelaide, SA, Australia
  3. Discipline of Surgery, The Queen Elizabeth Hospital, Woodville, SA, Australia

During the ovarian cycle, the mammary gland epithelium undergoes proliferation, differentiation and apoptosis under the direction of ovarian hormones, and this cellular turnover has been linked with the high susceptibility of the mammary gland to tumour formation. At the time of ovulation, the mammary epithelium exhibits a basic ductal structure. As circulating progesterone rises, epithelial proliferation and alveolar budding occurs. If pregnancy does not proceed, the fall in progesterone induces apoptosis of the newly formed alveolar buds, and the tissue is remodelled back to the basic architecture. Macrophages are immune system cells with multiple roles in epithelial cell turnover during ovarian cycle. Our transgenic mouse studies demonstrate that macrophages promote estradiol- and progesterone-induced epithelial cell proliferation and alveolar bud development following ovulation, and when progesterone levels fall towards the end of the cycle, macrophages promote phagocytosis of apoptotic cells and remodel the tissue to its basic architecture. These differing macrophage functions are associated with altered phenotype, with fluctuation in expression of MHCII, CD204 and NKG2D by mammary gland macrophages across the cycle under hormonal control. Fluctuations in macrophage phenotype and function are accompanied by alterations in the cytokine microenvironment in the mammary gland. The estrus phase of the ovarian cycle is relatively pro-inflammatory compared to other stages of the cycle, due to increased circulating estradiol during this phase. Furthermore, the estradiol-induced inflammatory cytokine microenvironment is significantly attenuated by progesterone. This fluctuation in the immune microenvironment over the course of the ovarian cycle implies that there is differential capability to recognize DNA-damaged cells, phagocytose dying epithelial cells and present antigens to generate adaptive immune responses. This changing immune microenvironment across the ovarian cycle is likely to reflect the requirement for macrophages to support tissue development versus tissue degeneration. However, this might also impact on immune responses to the early stages of tumorigenesis and dispose to the increased breast cancer susceptibility observed in women with increased number of years of menstrual cycling.