CCL2 and polycystic ovary syndrome: Additionally, PCOS endometrial stromal fibroblasts produce higher levels of IL-6, IL-8, MCP-1, and granulocyte-macrophage colony-stimulating factor (GM-CSF), which facilitate the maturation of endometrial DCs and macrophages, subsequently leading to progesterone resistance in the endometrium and impairing endometrial decidualization (57).