Whole endometrial fragments form characteristics of in vivo endometriosis in a mesothelial cell co-culture system: an in vitro model for the study of the histogenesis of endometriosis.

OBJECTIVE: We have previously reported on the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) on the adhesion of human endometrial stromal cells to peritoneal mesothelial cells in vitro. The relevance of this co-culture system to in vivo endometriosis remains to be established. We contrasted endometrial fragments with endometrial stromal cells to determine their relevance. METHODS: Human mesothelial cells were isolated from peritoneal fluid from four normal women via Ficoll-Paque gradient centrifugation at 400 x g for 30 minutes and grown in M199 medium containing epidermal growth factor (10 ng/mL) and 10% fetal calf serum. The homogeneous cells were cultured on collagen-coated plates until a monolayer formed. Endometrial stromal cells or whole endometrial fragments, isolated from endometrial tissue of four normal women, were put on the mesothelial monolayer and cultured at 37 degrees C for 24 days. After fixation, the samples were incubated with monoclonal antibody to epithelial membrane antigen, cytokeratin, and vimentin, and processed with standard immunohistochemical techniques. RESULTS: Observation under phase contrast microscopy revealed that, in this co-culture system, whole endometrial fragments demonstrated characteristic morphology of in vivo endometriosis, whereas isolated endometrial stromal cells did not. CONCLUSION: Whole endometrial fragments, but not isolated endometrial stromal cells, form morphologically characteristic structures similar to in vivo endometriosis in this co-culture system. It is hoped that this system might be useful for studying certain aspects of the histogenesis of endometriosis.