Molecular Characterization, Expression Responses and Antipathogenic Bacterial Function of Interleukin-1β (IL-1β) in Asian Seabass (Lates calcarifer Bloch, 1790).

In vertebrates, the interleukin-1β molecule (IL-1β) is among the most important proinflammatory cytokines and plays crucial roles in shaping injury progression, immunological challenges, and local and systemic responses to infection. In the current study, a cDNA encoding the IL-1β gene in Asian seabass (Lates calcarifer) (LcIL-1β) was identified at both the nucleotide and protein levels. Its immune responses were investigated in various tissues from diseased and normal fish. Recombinant rLcIL-1β was produced in Escherichia coli. Furthermore, its ability to control two fish pathogenic bacteria, Flavobacterium covae and Streptococcus iniae, was assessed in vitro. Transcriptional expression was quantified by qRT-PCR, which revealed the highest levels in whole blood, followed by the liver, gills and midgut. Immune response analyses of the head kidney, whole blood, liver, gills, spleen and intestines of fish infected with F. covae and S. iniae at concentrations of 1 × 103, 1 × 104 and 1 × 105 CFU/fish, respectively, revealed significant upregulation of LcIL-1β (p < 0.05) for 6-24 h (h) after induction. Interestingly, compared with the control treatment, the application of 1, 10 and 100 µg of rLcIL-1β greatly increased the phagocytic activity and phagocytic index of phagocytes (p < 0.05). Antibacterial function analyses of F. covae and S. iniae revealed minimal inhibitory concentrations (MICs) of 29.17 and 85.25 μg/mL, respectively. Finally, injection of S. iniae following rLcIL-1β revealed that 50 and 100 µg of the target protein demonstrated significant functional activity in safeguarding Asian seabass from these pathogenic bacteria (p < 0.05). This information revealed that LcIL-1β in Asian seabass significantly drives immune defense mechanisms against pathogenic bacteria, which is important for the development of effective disease prevention methods for Asian seabass aquaculture.