Interferon stimulated gene 15 expression at the human embryo−maternal interface

Purpose In early pregnancy the dialogue between maternal endometrium and embryo is a key process in establishing a receptive decidua and placental network. Decidual ISG15 induction is thought to promote pregnancy maintenance and development. ISG15 is involved in RNA splicing, cytoskeletal organization, stress response and further intracellular processes. Methods ISG15 expression was examined immunohistologically in paraffin-embedded human placental and decidual tissue samples of all pregnancy trimesters on adjacent sections (first trimester n = 5, second n = 5, third n = 3). Samples were processed using a protocol applying a rabbit polyclonal ISG15 antibody. A mouse monoclonal cytokeratin seven antibody was utilized to identify the different placental departments and decidual glands. Staining results and anatomical features were evaluated blindly with strict rating criteria. Results ISG15 expression was identified in first and second trimester tissue samples. ISG15 localized especially to the extravillous cytotrophoblasts in the maternal wall and in maternal blood vessel. Expression was detected in cytotrophoblast progenitor cells in the placental villi and the cell column with a maximum in the first trimester. The syncytial layer stained positive in first and second trimester samples. Third trimester samples showed no expression of ISG15 at all. Conclusions ISG15 abundance in the human placenta is an interesting finding, with implications for placental development, fetal growth and potential defense mechanism against infections. The maximal expression of ISG15 in the first and second trimester of pregnancy suggests that ISG function is needed when placental and embryo development is enormous and embryo susceptibility to external influences is high.