Insights into the functional role of grass carp IL‐8 in head kidney leukocytes: pro‐inflammatory effects and signalling mechanisms

Interleukin-8 (IL-8) is a critical chemokine regulating immune cells' chemotaxis as well as their physiological or pathological activations. In fish cells, recombinant IL-8 proteins induced transcriptions of pro-inflammatory cytokines. Nonetheless, the exact mechanisms underlying the function of fish IL-8 as a pro-inflammatory cytokine are still unclear. In this paper, the authors first prepared recombinant grass carp IL-8 (rgcIL-8) using an Escherichia coli expression system, and later confirmed rgcIL-8 increased gene expression of il8, il1β and tumour necrosis factor alpha (tnfα) in grass carp head kidney leukocytes (HKLs). Using signalling pathway inhibitors, the authors showed that rgcIL-8 regulated transcriptions of pro-inflammatory cytokines via MAPK and/or NF-κB signalling pathways. They cloned gcIL-8-specific receptor CXCR1 and subsequently discovered that gcIL-8 could increase the activity of NF-κB and the transcription of IL-1β via CXCR1. Simultaneously, antibody neutralization assay showed that endogenous IL-8 is partially relevant to the self-regulation of IL-1β. Moreover, rgcIL-8 led to the expression of inducible nitric oxide synthase gene, causing an accumulation of nitric oxide in the culture medium of HKLs, suggesting the potential of gcIL-8 to mediate inflammatory response. This study not only enriched the function of IL-8 in teleost but also revealed it as a potential target for the inflammatory control in grass carp.