Regulated C-C motif ligand 2 (CCL2) in luteal cells contributes to macrophage infiltration into the human corpus luteum during luteolysis

Intense macrophage infiltration is observed during luteolysis in various animals including women; however, we still do not know how macrophage infiltration into the human corpus luteum (CL) during luteolysis is regulated. In this study, we examined the expression, localization, and regulation of an important chemokine for the recruitment of monocyte/macrophage lineages, C-C motif ligand 2 (CCL2), in the human CL across the luteal phase and in cultured human luteinized granulosa cells (LGCs), with special reference to the number of infiltrating macrophages and luteal cell function. CCL2 mRNA increased in the non-functional regressing CL during menstruation (P<0.01), corresponding to an elevated mRNA expression of a macrophage-derived cytokine, TNF, and an increased number of infiltrating macrophages positively stained with a macrophage marker, CD68. CCL2 protein was immunohistochemically localized to the cytoplasm of granulosa-lutein and theca-lutein cells, and CCL2 mRNA was significantly reduced by hCG both in vivo (P<0.05) and in vitro (P<0.01). CCL2 was also down-regulated by luteotrophic prostaglandin (PG) E (P<0.0001), but up-regulated by luteolytic PGF (P<0.05) in vitro. Administration of TNF significantly enhanced the CCL2 mRNA expression in cultured LGCs (P<0.01). A greater abundance of infiltrating macrophages were found around granulosa-lutein cells lacking 3β-HSD or PGE synthase (PGES) immunostaining. CCL2 mRNA expression was negatively correlated with both HSD3B1 and PGES, suggesting that locally produced progesterone and PGE suppress macrophage infiltration into the CL. Taken together, the infiltration of macrophages in the human CL is regulated by endocrine and paracrine molecules via regulation of the CCL2 expression in luteal cells.