Soluble forms of NKG2D receptor ligands (MHC class I polypeptide-related sequence A [MICA], MICB, and UL16 binding protein 2 [ULBP-2]), found in elevated concentrations in peritoneal fluid of endometriosis patients, especially in deep infiltrative forms, can bind to NKG2D, causing its internalization and degradation (71). This evidence concerns the gene ULBP2 and endometriosis.