Recombinant anti-lipopolysaccharide factor isoform 3 and the prevention of vibriosis in the black tiger shrimp, Penaeus monodon

Anti-lipopolysaccharide factors are antimicrobial peptides previously identified in shrimps and other crustaceans. The high activity against a shrimp pathogenic bacterium, Vibrio harveyi, of the recombinant Penaeus monodon anti-lipopolysaccharide factor isoform 3 protein (rALFPm3) suggested its potential use in the control or prevention of outbreaks of vibriosis in shrimp farming. We further investigated its activity in vivo in terms of neutralization and protective effects in shrimps challenged with V. harveyi. Prior incubation of V. harveyi with rALFPm3 at concentrations of 6.25 µM or higher completely neutralized the bacteria's pathogenicity to shrimps as shown by 100% shrimp survival following systemic challenge with an otherwise lethal dose. Pre-injection of shrimps with rALFPm3 prior to V. harveyi infection reduced the cumulative mortality 2.4 fold compared to the control shrimps injected with saline solution, suggesting a potential prophylactic effect. The effects of rALFPm3 injection on the expression levels of five immune genes, ALFPm3, phagocytosis activating protein (PAP), prophenoloxidase activating enzyme (PPA), cytosolic manganese superoxide dismutase (SOD) and survivin were examined to detect changes in the different reactions of the shrimp immune responses. The results indicated that rALFPm3 is likely to affect various defense pathways. The present study suggests a potential use of rALFPm3 in therapeutic and pharmaceutical applications in aquaculture.