Insights into the functional role of grass carp IL-8 in head kidney leukocytes: pro-inflammatory effects and signaling 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. However, the exact mechanisms underlying the function of fish IL-8 as a pro-inflammatory cytokine are still unclear. In this paper, we first prepared recombinant grass carp IL-8 (rgcIL-8) using an E. coli expression system, and later confirmed rgcIL-8 increased gene expression of il8, il1β and tumor necrosis factor alpha (tnfα) in grass carp head kidney leukocytes (HKLs). Using signaling pathway inhibitors, we demonstrated that rgcIL-8 regulated transcriptions of pro-inflammatory cytokines via MAPK and/or NF-κB signaling pathways. We 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. This article is protected by copyright. All rights reserved.