A ROLE FOR GLYCOCONJUGATES IN HUMAN-DEVELOPMENT - THE HUMAN FETO-EMBRYONIC DEFENSE SYSTEM HYPOTHESIS

The mechanisms underlying the protection of the human embryo/fetus fro m the maternal immune response are poorly understood. Substantial evid ence indicates that carbohydrate recognition plays a primary role in t he sequestration of leukocytes during inflammatory processes, lymphocy te homing, and initial gamete binding. Our previous studies suggest a possible convergence in the types of carbohydrate sequences recognized during initial human gamete binding and immune/inflammatory cell inte ractions. Our more recent findings indicate that oligosaccharides part icipating in such processes are also associated with soluble glycoconj ugates found in the human placenta, amniotic fluid, and decidua. We th eorize that such glycoconjugates may abrogate the maternal immune/infl ammatory response by blocking the primary adhesive interactions requir ed for the expression of such activities. Foreign embryonic cells may also be protected by surface expression of oligosaccharide sequences t hat suppress immune effector cell action in a manner not dependent upo n classical major histocompatibility (MHC) recognition. Glycoconjugate s expressing selectin ligands may also manifest a potent contraceptive effect that may also be beneficial for both the mother and the develo ping embryo/fetus. This hypothesis provides a preliminary framework fo r understanding how temporally and spatially restricted immunosuppress ive effects could be expressed in utero that protect the human embryo/ fetus during this period of human development.