Immunohistological distribution of the secretory endometrial protein, 'pregnancy-associated endometrial alpha 2-globulin', a glycosylated beta-lactoglobulin homologue, in the human fetus and adult employing monoclonal antibodies

We have previously demonstrated that pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the human glycosylated beta-lactoglobulin homologue (HG-BLG), is quantitatively the major secretory soluble protein product of the secretory endometrium during the latter half of the menstrual cycle and decidua spongiosa of the gestational endometrium during early pregnancy, and is principally localized to the glandular epithelium. In the present study employing monoclonal antibodies in immunohistological techniques, the distribution and localization has been examined in normal and pathological tissues of the adult and first-trimester fetus. No significant staining for alpha 2-PEG was detected in any nonreproduction-associated tissue in the normal adult nor any tissue in the fetus. In the adult, most intense staining was associated with the endometrial glandular epithelium in the uterus or in ectopic sites in patients with endometriosis. During the menstrual cycle and pregnancy, appearance of alpha 2-PEG in endometriosis was strongly linked with its appearance in uterine endometrial tissue, suggesting that endometriotic tissue exhibited competence to respond to the same hormonal milieu required to induce synthesis in the uterine endometrium. Localization to the mucosal epithelium of the Fallopian tube was consistent with synthesis of alpha 2-PEG, albeit at low levels, and staining at this site reflected fluctuations of staining within the uterus. Of the pathological specimens examined, staining was only detected in a proportion of ovarian carcinomas. No staining was detected in the mammary gland, a site of beta-lactoglobulin synthesis, whether obtained during pregnancy or lactation.