 Other ApoD ligands include E-3-methyl-2-hexenoïc acid, a molecule present in axillary secretions; retinoic acid which is involved in cellular differentiation; sphingomyelin and sphingolipids which are major components of HDL and cell membranes.The fact that apoD may bind such a large variety of ligands strongly support the hypothesis that it could be a multi-ligand multi-function protein.APOD is a biomarker of androgen insensitivity syndrome (AIS).