Defensins are a group of small
antimicrobial peptides playing an important role in innate host defense. In this study, a β-
defensin cloned from liver of orange-spotted grouper, Epinephelus coioides, EcDefensin, showed a key role in inhibiting the
infection and replication of two kinds of newly emerging marine fish viruses, an enveloped DNA virus of Singapore grouper iridovirus (SGIV), and a non-enveloped RNA virus of viral nervous
necrosis virus (VNNV). The expression profiles of EcDefensin were significantly (P < 0.001) up-regulated after challenging with
Lipopolysaccharide (LPS), SGIV and
Polyriboinosinic Polyribocytidylic Acid (polyI:C) in vivo. Immunofluorescence staining observed its intracellular innate immune response to
viral infection of SGIV and VNNV. EcDefensin was found to possess dual
antiviral activity, inhibiting the
infection and replication of SGIV and VNNV and inducting a
type I interferon-related response in vitro. Synthetic
peptide of EcDefensin (Ec-
defensin) incubated with virus or cells before
infection reduced the viral infectivity. Ec-
defensin drastically decreased SGIV and VNNV titers, viral gene expression and structural
protein accumulation. Grouper spleen cells over-expressing EcDefensin (GS/pcDNA-EcDefensin) support the inhibition of
viral infection and the upregulation of the expression of host immune-related genes, such as
antiviral protein Mx and pro-inflammatory
cytokine IL-1β. EcDefensin activated type I IFN and
Interferon-sensitive response element (ISRE) in vitro. Reporter genes of IFN-Luc and ISRE-Luc were significantly up-regulated in cells transfected with pcDNA-EcDefenisn after
infection with SGIV and VNNV. These results suggest that EcDefensin is importantly involved in host immune responses to invasion of viral pathogens, and open the new avenues for design of
antiviral agents in fisheries industry.