Detection of pregnancy-specific β1 glycoproteins in human milk

We explored the possibility that normal human milk contained pregnancy-specific β1 glycoproteins (PSGs). PSGs have been identified previously in human placenta and serum samples from pregnant women by multiple antibody techniques, including immunohistochemical staining, Western blotting and ELISA. Molecular cloning of PSG-encoding cDNAs and genomic analysis has previously revealed that there are 12 PSG genes. The biological significance of PSG proteins is not yet known, but fetal nutritive and differentiating functions have been proposed. In our study, we detected a series of immunoreactive PSGs in human milk by Western blotting and ELISA. We then compared the pattern of PSGs in human placenta and milk by two-dimensional gel electrophoresis. Our results demonstrated a non-identical, but overlapping array of PSGs in human milk and human placenta. These findings are of interest in relation to previous studies which have identified certain growth factors and hormones that are common to both placenta and milk. We hypothesize that the identification of PSGs, delivered by two separate organs, both to the fetus and the neonate may provide further evidence for coordinated delivery of regulators of development of the baby, both within the mother and after birth. There may be coordination of the regulation of the mammary epithelial alveolar cell and the placental trophoblast to assist neonatal development and function.