Antimicrobial peptides/proteins in immune immune-related tissues of Atlantic cod (Gadus morhua L.): expression and function from a health perspective

The innate immune system comprises an arsenal of antimicrobial peptides (AMPs) and proteins (AMPPs) that provide protection against potential pathogens. In Atlantic cod (Gadus morhua), various AMPs and AMPPs have been characterised but knowledge of their biological functions still remains limited. In this study we present the transcriptional profiles of such molecules, including cathelicidin, β-defensin, hepcidin, piscidin-1 and -2, BPI/LBP and lysozyme, in immune-related tissues of Atlantic cod using qPCR analysis. Fish tissues were obtained from pre- or post- exposure to various stimuli (-glucan, inactivated and live pathogenic bacteria, live commensal bacteria), temperature rise and overcrowding conditions. Stimulation with either inactivated or live bacteria resulted in increased transcription levels of cathelicidin, hepcidin, BPI/LBP and lysozyme; however, tissue specificity and induction levels varied broadly among molecules. Depending on the type of tissue tested, those stimuli showed either suppressive or stimulatory effects in mRNA transcription of β-defensin and piscidin genes. In contrast, using temperature rise and overcrowding models, we detected different trends on AMP and AMPP expression levels in cod. These results point out the fact that cod AMPs and AMPPs can be regarded as inducible, constitutive or with overlapping roles in maintaining fish health and preventing diseases infection. Moreover, our data contributes for further understanding host defence in the complex aquatic environment.