Abstract

Antimicrobial peptides (AMP) play an essential role in the innate immune system, mod-ulating the defense response. In a previous study, we demonstrated the antimicrobial activity ofsynthetic hepcidin (hep20) from rainbow trout (Oncorhynchus mykiss), and its protective effect inEuropean sea bass (Dicentrarchus labrax) challenged withVibrio anguillarum. Additionally, we de-scribed the uptake and distribution of hep20 in different tissues and leukocyte cells. Interestingly,various AMPs characterized in high vertebrates, called host defense peptides (HDPs), also possessimmunomodulation activity. For that reason, the present study explores the immunomodulatoryabilities of hep20 throughin vitroandin vivostudies. First, a monocyte/macrophage RTS-11 cell linefrom rainbow trout was used to evaluate hep20 effects on pro- and anti-inflammatory cytokines in fishleukocyte cells. Next, the European sea bass juveniles were used to determine if hep20 can regulatethe expression of cytokines in fish immune tissues. The results show that hep20 was uptake innerto RTS-11 cells and was able to induce the expression of IL-10, IL-1β, and TNFαat transcriptionaland protein levels. Then, the European sea bass juveniles were given intraperitoneal injections ofthe peptide. At 1, 3, 7, 14, and 21 days post-injection (dpi), IL-10, IL -1β, and TNFαmRNA werequantified in the anterior gut, spleen, and head kidney. The hep20 was able to up-regulate cytokinegene expression in these tissues, mainly in the head kidney. Furthermore, the evaluated cytokinesshowed a cyclical tendency of higher to lesser expression. Finally, a bioinformatics analysis showedthat the structure adopted by hep20 is similar to theγ-core domain described for cysteine-stabilizedAMP, defined as immunomodulatory and antimicrobial, which could explain the ability of hep20 toregulate the cytokine expression. This study provides new insights into immunomodulatory functioncomplementary to the previously established antimicrobial activity of hep20, suggesting a role as anHDP in teleost fish. These facts are likely to be associated with molecular functions underpinning theprotective effect of fish hepcidin against pathogens.