Interaction between granulosa-lutein cells and monocytes regulates secretion of angiogenic factors in vitro

BACKGROUND Leukocyte infiltration and angiogenesis in the forming corpus luteum are prerequisites for normal ovarian function and may also underlie disorders like ovarian hyperstimulation syndrome. We examined whether ovarian angiogenesis could be affected by an interaction between granulosa-lutein (GL) cells and leukocytes. METHODS AND RESULTS We found that GL cells isolated from the follicular fluid synthesize and secrete the chemokine interleukin-8 (IL-8), which activates IL-8-receptor-specific Ca2+ and p38 mitogen-activated protein kinase signalling in monocytes and induces a directed migration of these cells towards the chemical gradient. Monocytes were found to further enhance IL-8 release, which suggests that these cells promote a massive leukocyte infiltration of the forming corpus luteum. A possible utility of leukocyte infiltration is the modulation of angiogenesis. We found that GL cells induce migration and capillary tube formation by endothelial cells in vitro. Furthermore, monocytes altered the profile of angiogenic factors released by GL cells, which supports the theory that an interaction between GL cells and leukocytes regulates ovarian angiogenesis. In addition, we found a correlation between increased secretion of pro-angiogenic cytokines and number of oocytes collected during IVF, which suggests that ovarian angiogenesis is related to the clinical response during ovarian stimulation. CONCLUSIONS An intricate communication may exist between infiltrating leukocytes and ovarian GL cells during the formation of corpus luteum, affecting neo-vascularization of the luteal tissue.