Analysis of In Silico Properties and In Vitro Immunomodulatory Effects of Seven Synthetic Host Defence Peptides in Gilthead Seabream (Sparus aurata) Leucocytes

Host defense peptides (HDPs) are vital to immunity due to their antimicrobial and immunomodulatory properties. While extensively studied in mammals, their immunomodulatory roles remain complex, and research on HDPs in fish is limited. This study aimed to predict physicochemical properties and mechanisms of action of seven HDPs in gilthead seabream (Sparus aurata): two piscidins (piscidin 1, piscidin 2) and five hepcidins (hepcidin H1, H2C, H2E, H2H, H2I). Predictions indicated heterogeneity among HDPs, all exhibiting antioxidant capacity and bioactive potential. In vitro analyses of these synthetic HDPs on head kidney leucocytes of gilthead seabream revealed minimal direct effects on leucocyte activities. RT-PCR gene expression analysis in leukocytes after 2 h of HDP incubation showed significant upregulation of bax-1 (hepcidin H2I), il-6 (piscidin 2), tnf-α (piscidin 1), tlr-7 (piscidin 1), and tlr-8 (piscidin 1), and downregulation of casp-3 (hepcidin H1), bcl-2 (hepcidin H2C), il-1β (hepcidin H1, H2C, H2E, H2H, H2I), tnf-α (piscidin 2, hepcidin H1, H2E, H2I), tlr-7 (piscidin 2, hepcidin H2E), and tlr-8 (piscidin 2, hepcidin H2H). The results indicate that HDPs demonstrate diverse immunomodulatory impacts on seabream white blood cells, playing a crucial role in regulating genes associated with programmed cell death, inflammatory responses, and Toll-like receptors. This complex function highlights the adaptability and significance of the studied HDPs in the immune system of gilthead seabream.