Decreased levels of the potent regulator of monocyte/macrophage activation, interleukin-13, in the peritoneal fluid of patients with endometriosis

Endometriosis is characterized by an increase in the number, activation and secretory activity of peritoneal fluid macrophages. Factors regulating the activation of these cells may be important in the pathophysiology of this disease. In this study we measured by enzyme-linked immunosorbent assay the concentrations of the macrophage inhibitory factor interleukin (IL)-13 in the peritoneal fluid of women with and without endometriosis. It was found that women with endometriosis had significantly lower amounts of IL-13 (95 ± 9.8 pg/ml) in peritoneal fluid, compared with women without endometriosis (115 ± 30 pg/ml) (P < 0.01). No cycle-specific variation was evident for either group. Another macrophage inhibitory interleukin (IL-10) was also measured, but no differences between women with (16.1 ± 13.2 pg/ml) or without (10.3 ± 5.6 pg/ml) endometriosis were seen. The immunolocalization of IL-13 was assessed in eutopic and ectopic endometrium and in isolated peritoneal fluid cells. Glandular epithelial cells and stromal cells in both eutopic and ectopic endometrium were immunopositive for IL-13. No cycle-specific differences in the immunolocalization of IL-13 were seen. In conclusion, the reduced amounts of IL-13 in the peritoneal fluid of women with endometriosis may lead to a lack of suppression of macrophage activation, thereby contributing to the overall pathogenesis of this disease.