15-lipoxygenase (ALOX15) can mediate a second lipoxygenation reaction where 17(S)-Hp-DHA is oxidised to the production of the protectin D1 (PD1) isomer PDX (Hong et al. 2003, Serhan et al. 2006, Chen et al. 2009). The chemical structure of PDX is 10(S),17(S)-dihydroxy-docosahexa-4Z,7Z,11E,13Z,15E,19Z-enoic acid. It differs from PD1, having E,Z,E geometry (PDX) instead of E,E,Z (PD1) and S configuration at carbon 10 instead of R (Chen et al. 2009). PDX is not a major product of leukocytes and has low potency compared to PD1 as a regulator of polymorphonuclear leukocyte (PMN) infiltration (Serhan et al. 2006).