Development of endometriosis-like lesions after transplantation of human endometrial fragments onto the chick embryo chorioallantoic membrane

The chick embryo chorioallantoic membrane (CAM) bioassay was used to invest igate the early pathogenesis of endometriosis, Endometrial fragments were e xplanted onto the CAM. The grafts including the surrounding CAM were excise d at 24, 48 or 72 h after explantation, fixed and embedded in paraffin, Imm unohistochemical analysis was used to distinguish endometrial cells, To ide ntify cells of human origin, in-situ hybridization was performed using a pr obe specific for human chromosome 1, After 24 h, direct contact between end ometrial stromal as well as epithelial cells and the mesenchymal layer of t he CAM was observed. Invasion of both stromal cells and intact endometrial glands into the mesenchymal layer was observed after 48 h, At 72 h, endomet riosis-like lesions were observed in the mesenchymal layer. Positive staini ng with antibodies to vimentin and pan-cytokeratin was observed in the inva ding cells as well as in the lesions. In the lesions these positively stain ed cells showed in-situ hybridization signals for human chromosome 1, confi rming their human origin, in conclusion, after 3 days of incubation, endome triosis-like lesions consisting of human endometrial glands and stromal cel ls were found in the mesenchymal layer of the CAM. These lesions apparently resulted from the invasion of intact human epithelial structures and strom al cells.