Identification and characterization of two novel antimicrobial peptides from Japanese sea bass (Lateolabrax japonicus) with antimicrobial activity and MO/MФ activation capability.

Piscidins participate in the innate immune response of fish, which aims to eliminate recognized foreign microbes and restore the homeostasis of immune system. We characterized two piscidin-like antimicrobial peptides (LjPL-3 and LjPL-2) isolated from Japanese sea bass (Lateolabrax japonicus). LjPL-3 and LjPL-2 showed different expression patterns in tissues. After Vibrio harveyi infection, the mRNA expression of LjPL-3 and LjPL-2 was upregulated in the liver, spleen, head kidney, and trunk kidney. The synthetic mature peptides LjPL-3 and LjPL-2 exhibited different antimicrobial spectra. Furthermore, LjPL-3 and LjPL-2 treatments decreased inflammatory cytokine production while promoting chemotaxis and phagocytosis in monocytes/macrophages (MO/MФ). LjPL-2, but not LjPL-3, displayed bacterial killing capability in MO/MФ. LjPL-3 and LjPL-2 administration increased Japanese sea bass survival after V. harveyi challenge, which was accompanied by a decline in bacterial burden. These data suggested that LjPL-3 and LjPL-2 participate in immune response through direct bacterial killing and MO/MФ activation.