Peroxiredoxins (Prx) are a family of antioxidant proteins also involved in inflammation and innate immunity. Prx1 and Prx2 are also known as natural killer enhancing factor (NKEF)-A and NKEF-B, respectively, by their ability to prime the mammalian NK-cells activity. In teleost fish, NKEF genes have been isolated but their regulation has been scarcely evaluated. We have identified orthologues of the NKEF-A and NKEF-B genes in the teleost European sea bass (Dicentrarchus labrax) which showed constitutive expression and wide distribution in their tissues. In vitro, the gilthead seabream (Sparus aurata) and sea bass NKEFs were slightly up-regulated in head-kidney leucocytes after stimulation with unmethylated CpG oligodeoxynucleotides, poly I:C or pathogenic bacteria. In vivo, seabream and sea bass infection with nodavirus up-regulated the expression of NKEF genes in the brain (target tissue for nodavirus) and head-kidney at different infection times. Although further studies are necessary to ascertain their role as antioxidant proteins and in the immune response in teleost fish, our results suggest a primary role of seabream and sea bass NKEFs in the innate immune response against bacterial and viral agents. Mol Immunol. 2013 Mar 16. pii: S0161-5890(13)00054-0. doi: 10.1016/j.molimm.2013.02.009. Esteban MA, Chaves-Pozo E, Arizcun M, Meseguer J, Cuesta A. Fish Innate Immune System Group, Department of Cell Biology and Histology, Faculty of Biology, Campus Regional de Excelencia Internacional "Campus Mare Nostrum", University of Murcia, 30100 Murcia, Spain.