Immunohistochemical localization of two endometrial proteins in the early days of human pregnancy.

Insulin-like growth factor binding protein-1 (IGFBP-1) [also known as placental protein 12(PP12)] and placental protein 14 (PP14) have been identified by specific immunostaining in early pregnancy specimens obtained 13-35 days of gestation. PP12 was evident in a discrete number of stromal decidual cells at the deciduotrophoblastic interface and under the endometrial surface epithelium. These cells did not have the rounded appearance of classic decidual cells but most often displayed cytoplasmic expansions. Staining for PP14 was strictly localized to the glandular epithelium of the endometrium. Implantation of the conceptus may be an important mechanism in the early expression of PP12 but not PP14.