Metabolic , Endocrine and Genitourinary Pathobiology Interleukin-4 Stimulates Proliferation of Endometriotic Stromal Cells

Several lines of evidence indicate that the Th2 immune response is associated with endometriosis. Although an increased concentration of interleukin (IL)-4, a typical Th2 cytokine, has been reported in endometriotic tissues, the implication of this for endometriosis has not been determined. To investigate a possible role of IL-4 in the development of endometriosis, we examined the presence of IL-4-producing cells in endometriotic tissues and the effect of IL-4 on proliferation of endometriotic stromal cells. Endometriotic stromal cells were isolated from endometriotic tissues obtained from women undergoing surgery for endometrioma. Immunohistochemistry of endometriotic tissues revealed that IL-4-positive cells were abundant in the stroma. The effect of IL-4 on proliferation of endometriotic stromal cells was studied using cell counting and BrdU incorporation assays. IL-4 (0.1 to 10 ng/ml) significantly increased cell number and BrdU incorporation in a dose-dependent manner, and the proliferative effect of IL-4 was inhibited by anti-IL-4 receptor antibody. IL-4-induced activation of mitogen-activated protein kinases in endometriotic stromal cells was examined by Western blotting. IL-4 induced phosphorylation of p38 mitogen-activated protein kinase, stress-activated protein kinase/c-Jun kinase, and p42/44 mitogen-activated protein kinase and inhibitors of these kinases suppressed IL-4-induced proliferation of endometriotic stromal cells. These findings suggest that proliferation of endometriotic stromal cells induced by locally produced IL-4 is involved in the development of endometriosis. (Am J Pathol 2008, 173:463–469; DOI: 10.2353/ajpath.2008.071044) Endometriosis is an enigmatic disease that deteriorates the health of women of reproductive age. A widely believed etiology is that endometrial debris in retrograde menstruation implants, survives and grows in the peritoneal cavity. However, it remains unknown why endometrial implants develop to substantial endometriotic lesions. Numerous lines of evidence suggest that aberrant immune responses and inflammatory reactions are involved in the pathogenesis of endometriosis. Women with endometriosis have characteristics of autoimmune disease, such as increased polyclonal B-cell activity, abnormalities in Tand B-cell function, and familial inheritance. High prevalence of autoimmune disease in endometriotic women supports an autoimmune aspect of endometriosis. Allergies and asthma are also reported at high rates in endometriotic women. In addition, a recent genome-wide transcriptional profiling study revealed that endometriosis exhibits a gene expression signature reminiscent of other autoimmune disorders. It is well known interleukin (IL)-4 is a distinguished molecule in autoimmunity and allergy. In view of the autoimmune and allergic background of endometriotic women, IL-4 is speculated to play a role in the pathogenesis of endometriosis. The notion is underpinned by the evidence that the levels of IL-4 mRNA and protein in peripheral blood monocytes and peritoneal fluid cells are elevated in women with endometriosis. However, localization of IL-4 and effects of IL-4 in endometriotic cells have been unknown. IL-4 exerts its effect on immune cells. In addition, actions of IL-4 on several nonimmune cells have been reported. Interestingly, IL-4 stimulates or inhibits cell proliferation in different cells and settings. The biological function of IL-4 is mediated by a specific IL-4 receptor that is linked to several different intracellular