Soluble HLA-G molecules in follicular fluid: a tool for oocyte selection in IVF?

Currently, different approaches are used to select oocytes for in vitro fertilization (IVF) procedures, but they do not assure a significant association with the pregnancy outcome. Since several studies have proposed the expression of HLA-G antigens in early embryos as a possible marker of elevated implantation rate, we investigated the presence of soluble HLA-G molecules in 50 follicular fluids (FFs). The results showed soluble HLA-G antigens (sHLA-G) in 19/50 (38%) FFs. Furthermore, we related the presence of sHLA-G molecules in FFs to the detection of the soluble antigens in the culture supernatants of the corresponding fertilized oocyte, evidencing a significant relationship (p=1.3 x10-6; Fisher exact p test). Specific ELISA and Western Blot approaches identified both HLA-G5 and soluble HLA-G1 molecules in FFs while immunocytochemical analysis proposed polymorphonuclear-like and granulosa cells as responsible for the production of sHLA-G1 and HLA-G5 molecules. In contrast, only sHLA-G1 antigens were detected in culture supernatants of fertilized oocytes. Overall, the results suggest a role for sHLA-G molecules in the ovulatory process and propose the FFs analysis for sHLA-G molecule presence as a useful tool for oocyte selection in IVF.