Primed humoral immune responses confer an increased early resistance to Vibrio parahemolyticus reinfection in mud crab (Scylla paramamosain)

Immune priming (IP) has been demonstrated to initiate more robust immune responses and protect invertebrates against recurrent infections, suggesting a potential strategy to prevent infectious diseases. In mud crab ( Scylla paramamosain ) aquaculture, Vibrio spp. are representative pathogens that cause high mortality and heavy economic losses. To establish a priming-based method for controlling vibriosis, the survival and humoral responses of mud crabs primarily exposed to formalin-killed Vibrio parahemolyticus (IP) and secondarily challenged with live bacteria (lethal challenge, LC) were examined in this study. The IP-stimulated crabs showed a significant improvement in cumulative survival. The antibacterial activity of hemolymph serum was enhanced in the early stages of IP and LC. The mRNA expressions of antimicrobial peptides and components in the TLR2-Myd88-Pelle-Dorsal cascade were significantly increased. IP evoked a faster and stronger response in the melanization cascade regulated by the prophenoloxidase system. The melanin level and phenoloxidase activity were elevated after LC, and the expression of certain related genes exhibited a greater and longer-lasting upregulation. IP also triggered a higher production of oxygen-derived free radicals and then activated the antioxidant enzyme system. The activity and expression of catalase and peroxidase were markedly increased in the primed crabs during early infection stage. The presented results suggest the effective protection of IP immunization against reinfections in mud crab, and the improved survival is largely attributable to an early-strengthened humoral immunity. These findings also provide a new understanding of the mechanisms of IP and contribute to creating a system approach for disease control management in crustacean aquaculture. • Immune priming effectively protected mud crabs against V. parahemolyticus reinfection. • Immune priming increased hemolymph antibacterial activity by upregulating AMP-related genes. • Immune priming activated the melanization cascade and antioxidant responses upon reinfection. • The improved survival of primed crabs is attributable to an early-phase enhanced humoral immunity.