Immunohistochemical localization of insulin-like growth factors (IGFs) and IGF binding proteins -1, -2 and -3 in human placenta and fetal membranes

Insulin-like growth factor (IGF) I and II are synthesized within the placenta and are believed to play an important role in the regulation of placental growth and endocrine function. IGF bioavailability is determined at a cellular level by several specific binding proteins (IGF BPs), which are widely but selectively distributed in all developing tissues. We have used immunohistochemistry to localize IGF I and II peptides, and IGF BP-1, -2, and -3 in human placentae, fetal membranes and umbilical cord at 6-8 weeks after therapeutic termination and at term after spontaneous delivery. Primary antisera were directed against human IGF I, human IGF BP-1, bovine IGF BP-2, and human IGF BP-3 respectively. Immunoreactive IGF BP-2 was found in association with the syncytiotrophoblast, intermediate trophoblasts of the fetal villi and chorion, amnion and decidua; while weaker staining was seen in some but not all cytotrophoblasts. A similar but less intense staining pattern was observed for IGF BP-1 and IGF peptides in placenta and amnio-chorion. Strong immuno-staining for IGF BP-1 was seen in decidual cells. No immunoreactive IGF BP-3 was found in placenta or membranes. A co-distribution of IGF BP-2, BP-1 and IGF peptides in placenta suggests a role for these IGF BPs in determining the localization of the IGFs for actions on target tissues.