Induced expression of cathelicidins in trout (Oncorhynchus mykiss) challenged with four different bacterial pathogens

Cathelicidins are an important family of antimicrobial peptide effectors of innate immunity in vertebrates. Two members of this group, CATH‐1 and CATH‐2, have been identified and characterized in teleosts (ray‐finned fish). In this study, we investigated the expression of these genes in different tissues of rainbow trout challenged with 4 different inactivated pathogens. By using qPCR, we detected a strong induction of both cath‐1 and cath‐2 genes within 24 hours after intraperitoneal inoculation with Lactococcus garvieae, Yersinia ruckeri, Aeromonas salmonicida, or Flavobacterium psychrophilum cells. Up to 700‐fold induction of cath‐2 was observed in the spleen of animals challenged with Y. ruckeri. Moreover, we found differences in the intensity and timing of gene up‐regulation in the analyzed tissues. The overall results highlight the importance of cathelicidins in the immune response mechanisms of salmonids.