HLA-G and endometriosis: Soluble levels of the NK cell inhibitory ligand HLA-G were also investigated by Rached et al. [18] in serum, using ELISA, reporting significantly higher levels of sHLA-G in sera in the endometriosis group compared with the controls (9.3 U/mL (1.2–192.6) vs. 6.1 U/mL (1.0–36.9), p = 0.013).