Immunohistochemical localization of the insulinlike growth factor binding protein-1 in female reproductive tissues by monoclonal antibodies

Human insulinlike growth factor binding protein-1 (hlGFBP-1) is a secretory protein that modulates the receptor-binding and biological actions of the insulinlike growth factor I (IGF-I). Human endometrium expresses the mRNA for IGFBP-1, and this protein is secreted by the secretory phase and pregnancy endometrium as well as by ovarian granulosa cells in vitro. In this study, we examined the cellular localization of IGFBP-1 in female reproductive tissues by using a purified monoclonal antibody Mab 6303 with an immunoperoxidase technique. Proliferative- and early secretory-phase endometrium as well as all extrauterine tissues except decidualized cells at the implantation site on the ovaries of ovarian pregnancies were negative for IGFBP-1. In midsecretory-phase endometrium, focal staining was first observed in the cytoplasm of glandular epithelial cells, with weaker staining in the stromal cells. In late secretoryphase endometrium, strong immunostaining was observed in predecidualized stromal cells, with weak focal staining remaining in some of the glandular epithelial cells. In early pregnancy, intense staining was detected in the cytoplasm of decidualized stromal cells of zona compacta in each sample, whereas the nondecidualized stromal cells remained unstained. Strong to medium staining was detected simultaneously in the glandular epithelial cells in 70% of the early pregnancy specimens. In term pregnancy, IGFBP-1 was localized in decidual cells of placental bed and decidua parietalis. Immunolocalization of IGFBP-1 to both endometrial epithelial and stromal cells, although only stromal cells express the gene of IGFBP-1 [14], supports the hypothesis of paracrine actions between these cells. The localization of IGFBP-1 to decidualized cells at the extrauterine implantation sites implies its association with decidual differentiation.