First trimester histiotrophe shows altered sialylation compared with secretory phase glycoconjugates in human endometrium.

OBJECTIVES: Histiotrophe is now recognized as being an important feature of early human pregnancy, providing nutrients and growth factors to the developing embryo. Our aim was to examine the glycan composition of histiotrophe from first trimester decidua and to compare it with secretions present in endometrial glands from the late secretory phase of the menstrual cycle. STUDY DESIGN: Twenty samples of decidua from pregnancies between 8 and 11 weeks were processed into epoxy resin and sections stained with a panel of 22 lectins, together with six late secretory phase endometrial biopsies. MAIN OUTCOME MEASURES: Specimens were analysed using a semi-quantitative ranking system and the density of lectin binding to the glandular secretions and the epithelium assessed. RESULTS: With the onset of pregnancy, beta-galactose, alpha-N-acetyl galactosamine and N-Acetyl lactosamine bound by Arachis hypogaea, Glycine max, Helix pomatia and Erythrina crystagalli agglutinins appeared in terminal positions on oligosaccharide chains, suggesting loss of the capping sialic acid residues present in the non-pregnant state. CONCLUSIONS: Suppression of terminal sialylation is evident during early pregnancy, suggesting that modifications to endometrial glandular activity occur in response to placental signals. The changes may facilitate absorption of histiotrophe by the trophoblast and enhance availability of substrates for degradation.