HLA-G expression is a fundamental prerequisite to pregnancy

HLA-G antigens are thought to play a key role in implantation by controlling trophoblasts invasion and maintaining a local immunosuppressive state. The secretion of soluble HLA-G antigens (sHLA-G) by early embryos seems necessary for a successful implantation and could be a marker of increased pregnancy rate following in vitro fertilization. We have reviewed the results obtained during the last years. They overall confirmed the predictive role of sHLA-G production in pregnancy outcome. Furthermore, we have examined the technical procedures utilized with a particular attention to the monoclonal antibodies employed in the ELISA techniques. New functional roles for HLA-G molecules in pregnancy could be suggested by the relationship observed between the presence of sHLA-G antigens in follicular fluids and sHLA-G expression in the corresponding fertilized oocyte. Furthermore, since maternal mRNA is fundamental for proteins production in early embryos, the biological role of the HLA-G 14bp polymorphism could be explored.