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

## TL;DR

This study identifies and characterizes the IL-1β gene in Asian seabass and shows it helps fight bacterial infections, which could improve aquaculture disease prevention.

## Contribution

The study provides the first molecular characterization and functional analysis of IL-1β in Asian seabass, revealing its role in immune defense against bacterial pathogens.

## Key findings

- LcIL-1β expression was highest in whole blood and significantly upregulated in response to bacterial infection.
- Recombinant LcIL-1β enhanced phagocytic activity and reduced bacterial growth in vitro.
- Injections of rLcIL-1β significantly protected Asian seabass from infection by S. iniae.

## Abstract

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.