New insight into the biological activity of Salmo salar NK-lysin antimicrobial peptides

NK-lysin is a potent antimicrobial peptide (AMP) with antimicrobial activity against bacteria, fungi, viruses, and parasites. NK-lysin is a type of granulysin, a member of the saposin-like proteins family first isolated from a pig's small intestine. In previous work, for the first time, we identified four variants of from Atlantic salmon ( ) using EST sequences. In the present study, we reported and characterized two additional transcripts of from . Besides, we evaluated the tissue distribution of three from and assessed the antimicrobial, hemolytic, and immunomodulatory activities and signaling pathways of three NK-lysin-derived peptides. The synthetic peptides displayed antimicrobial activity against (LF-89) and . These peptides induced the expression of immune genes related to innate and adaptive immune responses and . The immunomodulatory activity of the peptides involves the mitogen-activated protein kinases-mediated signaling pathway, including p38, extracellular signal-regulated kinase 1/2, and/or c-Jun N-terminal kinases. Besides, the peptides modulated the immune response induced by pathogen-associated molecular patterns (PAMPs). Our findings show that NK-lysin could be a highly effective immunostimulant or vaccine adjuvant for use in fish aquaculture.