Human 'pregnancy-associated endometrial alpha 1-globulin', a 32 kDa insulin-like growth factor-binding protein: immunohistological distribution and localization in the adult and fetus.

We have previously shown that pregnancy-associated alpha 1-globulin, a small molecular weight (32 kDa) insulin-like growth factor-binding protein (IGF-BP), is quantitatively the major secretory protein product of the decidualized endometrium during human pregnancy and is localized principally in the decidual cell. In the present study, employing monoclonal antibodies in immunohistological techniques, the distribution and localization of IGF-BP has been examined in normal and pathological tissues of the adult and first trimester fetus. In the adult, most intense reactivity was associated with endometrial stroma and their derived decidual cells in the uterus or in ectopic sites in patients with endometriosis. During the menstrual cycle, the appearance of IGF-BP in endometriotic tissue was linked with its appearance in uterine endometrial tissue. The only other adult cells where significant staining was detected was in the luteal cells of the corpus luteum. Production of the protein was not a feature of carcinomas. In the fetus, the protein was localized in lymphoid-myeloid progenitor cells and hepatocytes of the liver and at lower levels in testicular Leydig cells and adenocortical cells. These observations suggest highly specific tissue expression of this protein and support a specialized role for this protein in progenitor cells of the lymphomyeloid system, in certain steroid hormone-producing cells and in the decidual cell in pregnancy.