Anti-SOX21 antibodies are used in the immunodetection of the protein SRY-box transcription factor 21. In humans, the canonical protein has a reported length of 276 amino acid residues and a mass of 28.6 kDa. Its subcellular localization is in the nucleus. SOX21 is believed to play a role as an activator of transcription of OPRM1. Synonyms for this target antigen include transcription factor SOX-21, SOX-A, SRY (sex determining region Y)-box 21, SRY-box 21, and SOX25.