Human 'pregnancy-associated endometrial alpha 1-globulin', an insulin-like growth factor-binding protein: immunohistological localization in the decidua and placenta during pregnancy employing monoclonal antibodies.

We have previously shown that pregnancy-associated endometrial alpha 1-globulin, a small molecular weight insulin-like growth factor-binding protein (IGF-BP), is quantitatively the major secretory protein product of the decidualized endometrium during human pregnancy. In the present study, employing monoclonal antibodies raised against this protein in an immunohistological technique, the cellular localization of the protein has been examined in the decidua and placenta during pregnancy. During the first trimester the protein was principally associated with the decidual cell in the decidualized decidua compacta region of the endometrium with both cytoplasmic and extracellular matrix-associated staining patterns being detected. No extensive staining was observed in the placenta. At term the protein was localized in similar cells in the placental bed and endometrium associated with the amniochorion but not in the placenta. These studies suggest that the decidual cell represents the major source of IGF-BP during pregnancy and have relevance to the origin of amniotic fluid IGF-BP and the paracrine role of the decidual cell in the control of trophoblast growth.