Trimeric leukotriene C4 synthase (LTC4S trimer), located on the ER membrane, can catalyse the transfer of a glutathionyl group from glutathione (GSH) to 13(S),14(S)-epoxy-docosahexaenoic acid (13(S),14(S)-epoxy-DHA) to form maresin conjugates in tissue regeneration 1 (MCTR1) (Dalli et al. 2014, 2016a, 2016b). Incubation of human macrophages with LTC4S inhibitors significantly reduces cysteinyl leukotriene production and increases resolvin and lipoxin production (Dalli et al. 2016a). MCTR1, given to mice with E. coli peritonitis, showed potent proresolving action in inflammation and infections. With human macrophages, MCTR1 stimulated efferocytosis of apoptotic cells (Dalli et al. 2014).