Eosinophil peroxidase (EPX or EPO) is an eosinophil-derived granule protein that utilises H2O2 as an oxidising substrate to generate potent oxidising species. This mechanism is used by eosinophils to kill parasites and microbes [, ]. Besides using bromide as substrates to generate hypobromite (hypobromous acid), EPX can also oxidise thiocyanate (SCN-) ions to generate HOSCN-, which may induce the prothrombotic and proinflammatory endothelial and endocardial phenotypes responsible for thrombotic complications in the hypereosinophilic syndrome (HES) []. EPX is involved in both anti-inflammatory and pro-inflammatory activities [, ]. It may also play an important role through the production of reactive brominating species in asthma [, ]. It is required for eosinophilopoiesis in mice [].
