The M2 polarization of macrophage induced by fractalkine in the endometriotic milieu enhances invasiveness of endometrial stromal cells.

Fractalkine (FKN) is involved in the immunopathogenesis of inflammatory diseases, including endometriosis. Our objective was to investigate the role of FKN in the cross-talking between endometrial stromal cells (ESCs) and U937 (macrophage line) in the endometriotic milieu. We have found that FKN levels in peritoneal fluid and ESCs positively correlate with the progress of endometriosis. The expression of CX3CR1 in the normal ESCs were significantly lower than that in eutopic and ectopic ESCs from women with endometriosis. CX3CR1 expression in U937 was higher than that in ectopic ESCs. FKN secreted by eutopic ESCs could change the balance between the release of IL10 and IL12 of macrophages with the upregulation of IL10 production and downregulation of IL12 production. Moreover, FKN could induce M2 polarization of macrophage with decreased expression of CD86. FKN could increase the expression of matrix metalloproteinase 9 and decrease the expression of tissue inhibitor of metalloproteinase1 and 2, and promote the invasiveness of ESCs by activating p38MAPK and integrinβ1 signal pathway. In conclusion, the higher levels of FKN secreted by eutopic ESCs facilitate the onset and progression of endometriosis by inducing M2 polarization of macrophage which in turn enhances invasiveness of ESCs.