Identification, Expression and Antimicrobial Functional Analysis of Interleukin-8 (IL-8) in Response to <i>Streptococcus iniae</i> and <i>Flavobacterium covae</i> in Asian Seabass (<i>Lates calcarifer</i> Bloch, 1790)

Abstract

In this research, the proinflammatory cytokine interleukin-8 (IL-8) was shown to play a key role in inflammatory responses in fish. This study involved the cloning of the gene that encodes IL-8 in Asian seabass (Lates calcarifer) as well as analyses of its expression and function in this fish. The expression levels of LcIL-8 indicated that it was broadly expressed in most analyzed tissues, with the most predominant expression in the whole blood 6 to 24 h after infection with S. iniae at concentrations of 105 colony-forming units (CFU)/fish (p F. covae, the LcIL-8 transcript was upregulated in the gills, liver and intestine, and the highest expression level was observed in the gills. However, LcIL-8 was downregulated in all the tested tissues at 48 and 96 h after infection with the two pathogenic strains, indicating that Lc-IL8 has a short half-life during the early immune responses to pathogens. Moreover, the MIC of the rLcIL-8 protein against S. iniae was 10.42 ± 3.61 µg/mL. Furthermore, functional analyses clearly demonstrated that 10 and 100 µg of the rLcIL-8 protein efficiently enhanced the phagocytic activity of Asian seabass phagocytes in vitro (p S. iniae following the rLcIL-8 protein indicated that 50 and 100 µg of rLc-IL-8 were highly effective in protecting fish from this pathogen (p LcIL-8 possesses a biological function in the defense against bacterial infections in Asian seabass.

Keywords

• proinflammatory cytokine
• interleukin-8
• Asian seabass
• <i>Streptococcus iniae</i>
• <i>Flavobacterium covae</i>
• antimicrobial activity