Characterization of NK-lysin from Sevenband grouper, Hyporthodus septemfasciatus against NNV infection

Abstract

In fish, the innate immune system plays a more fundamental and crucial role than the acquired immune system during infection of pathogens. NK-lysin is a new antimicrobial peptides (AMPs) that play an important role in host innate defense against various pathogens. Although its best-known function is as AMP against bacteria, recent studies point to a special role of NK-lysin in antiviral response. In this study, we identified an NK-lysin (HS.NKL) from the seven-band grouper (Hyporthodus septemfasciatus) and analyzed its expression profiles and antiviral activities. The open reading frame of the HS.NKL cDNA sequence was 510 bp in length, coding 169 amino acids. The mature peptide of HS.NKL has six well-conserved cysteine residues and shares a Saposin B domain, characteristic of Saposin-like protein (SALIP) family. Under normal physiological conditions, HS.NKL transcription in fish tissues was highly expressed in spleen, heart, and gill. In NNV infection, the expression profiles of HS.NKL significantly increased in the brain, indicating its role in the immune response. Further studies showed that the expression of HS.NKL in SSN-1 cell significantly delayed the cytopathic effect (CPE) progression evoked by NNV, but the difference in the transcription of the viral gene was not significant. Therefore, further study is needed to prove the antiviral mechanism of HS.NKL. These results indicate that HS.NKL might play a functional role in NNV infection.