Roles of interleukins in antibacterial immune defense of the brood pouch in the lined seahorse Hippocampus erectus

Seahorse embryos are brooded in the enclosed nutrient-rich environment of the male brood pouch, which may be prone to bacterial infection. The immune responses of interleukin (IL) genes in the brood pouch have not been well studied. We identified 13 interleukins in the lined seahorse Hippocampus erectus. Tissue-specific expression analysis revealed increased mRNA expression levels of il-1β, il-18, and il-8 in the brood pouch. When challenged with lipopolysaccharide or Vibrio parahaemolyticus, il-1β and il-18 were active as part of the acute and chronic inflammatory responses, respectively. Importantly, il-8 may be involved in powerful antibacterial immune responses and may be induced by il-1β and il-18 via a process involving the nuclear factor-κB signaling pathway. These results suggest that il-1β, il-18, and il-8 may play key roles in the antibacterial immune defense of the brood pouch in male seahorses.