We cloned and sequenced 2C I-IFN, a two-cysteine containing type I interferon (I-IFN) gene, in orange-spotted grouper (Epinephelus coioides). The cDNA has 769 base pairs, the protein has 172 amino acids, and the predicted signal peptide has 18 amino acids with two cysteines. This gene is similar to I-FNs from sea bass and other teleosts. 2C I-IFN has 5 exons and 4 introns, also similar to other teleost I-IFNs. Immunohistochemical (IHC) analysis indicated that expression is predominantly membrane-localized in healthy grouper, but has a zonal distribution in nodavirus-infected grouper. Grouper infected with nodavirus had elevated levels of 2C I-IFN at 72 h and Mx at days 6-7. Recombinant 2C I-IFN activated grouper Mx, leading to upregulated antiviral activity. The grouper Mx promoter was highly induced after treatment with recombinant 2C I-IFN. The present results suggest that expression of grouper 2C I-IFN may participate in the immunologic barrier function against nodavirus.,Copyright © 2014 Elsevier Ltd. All rights reserved.