Functional characterization of IL-17D in chub mackerel (Scomber japonicus): expression profiles, immunomodulatory...

Interleukin-17D (IL-17D) is a pro-inflammatory cytokine implicated in T helper 17 cell-mediated immune responses. Although its role in mammalian immunity is well established, its function in fish remains relatively unexplored. This study delves into the functional characteristics of IL-17D in chub mackerel (Scomber japonicus). We identified and characterized a chub mackerel IL-17D homolog (SjIL-17D) and investigated its spatial and temporal expression patterns, as well as the impact it has on downstream gene expression, apoptosis, cell proliferation, and nitric oxide (NO) production. SjIL-17D exhibited a wide tissue distribution, showing the highest expression in the blood, followed by the brain and skin. Upon immune challenges with polyinosinic:polycytidylic acid, lipopolysaccharide (LPS), Vibrio harveyi, and Streptococcus iniae, SjIL-17D expression was significantly upregulated in the blood. Functional analysis revealed that recombinant SjIL-17D (rSjIL-17D) stimulated the expression of pro-inflammatory cytokines, transcription factors, mitogen-activated protein kinases, and antiviral response genes in fish cell lines. Furthermore, rSjIL-17D attenuated LPS-induced apoptosis, promoted M1 macrophage polarization, and enhanced wound healing. Additionally, rSjIL-17D was found to stimulate NO production in macrophages and exhibit antiviral activity against viral hemorrhagic septicemia virus. These findings collectively demonstrate the crucial role that IL-17D plays in regulating immune responses in chub mackerel, providing valuable insights into the innate immune mechanisms of this economically important fish species.