Analysis of Manifestation of CC and CXC Chemokine Genes in Olive Flounders (Paralichthys olivaceus) Artificially Infected with VHSV during the Early Developmental Stage

Comparative transcriptome analysis reveals potential anti-viral immune pathways of turbot (Scophthalmus maximus) subverted by megalocytivirus RBIV-C1 for immune evasion

Successful viral infection and multiplication chiefly rely on virus subversion mechanisms against host anti-viral immune responses. In this study, in order to reveal the anti-viral immune-related pathways suppressed by megalocytivirus infection, transcriptome analysis was performed on the head-kidney of turbot (Scophthalmus maximus) infected with lethal dose of RBIV-C1 at 3, 6 and 9 days post challenge (dpc). The results showed that, compared to unchallenged groups, 190, 1220, and 3963 DEGs were detected in RBIV-C1 infected groups at 3, 6 and 9 dpc, respectively, of which, DEGs of complement components and pattern recognition proteins were up-regulated at 3 dpc and down-regulated at 6 and 9 dpc, DEGs of cytokines were up-regulated at 6 dpc and down-regulated at 9 dpc. Expression trend analysis revealed that DEGs of profiles 9 and 13 featured decreased expression patterns and were significantly enriched into 10 immune-related pathways, i.e., complement and coagulation cascades, cytokine-cytokine receptor interaction, chemokine signaling pathway, B/T cell receptor signaling pathway, antigen processing and presentation, and so on. Further co-expression network analysis (WGCNA) revealed positive correlated innate immune related pathways at 3 and 6 dpc, and negative correlated innate and adaptive immune related pathways at 9 dpc. This study revealed a set of anti-viral immune genes/pathways that would also be potential targets subverted by RBIV-C1 for immune evasion, which can serve as a valuable resource for future studies on the molecular mechanisms of anti-viral immune defense of turbot and immune escape of megalocytivirus.

Molecular cloning and characterization of chemokine C-C motif ligand 34 (CCL34) genes from olive flounder (Paralichthys olivaceus)

Chemokines are a superfamily of chemotactic cytokines that regulate the migration and immune responses of leukocytes. Depending on the arrangement of the first two cysteine residues, chemokines are divided into four groups: CXC (α), CC (β), C (γ), and CX3C (δ). Chemokine C-C motif ligand 34 (CCL34) is a member of the CC chemokine family and is known as a fish-specific CC chemokine. In this experiment, we analyzed the molecular cloning and characterization of the PoCCL34 gene in olive flounder (Paralichthys olivaceus), including CCL34a.3 (PoCCL34a.3) and CCL34b.3 (PoCCL34b.3). The amino acid sequence of PoCCL34 has four highly conserved cysteine residues and it has a C-C motif. Phylogenetic analysis revealed that PoCCL34 was phylogenetically clustered in the fish CCL34 subcluster. Recombinant PoCCL34 induced chemotaxis of head kidney leukocytes in a dose-dependent manner. Head kidney leukocytes stimulated with PoCCL34 also exhibited significant respiratory burst activity and increased expression of pro-inflammatory cytokines (IL-1β, IL-6, and CXCL8), but the overall expression of interferon-related genes (IFN-α/β, IFN-γ, Mx, and ISG15) did not increase. Olive flounder injected with recombinant PoCCL34 demonstrated increased expression of pro-inflammatory cytokines (IL-1β and IL-6) in the head kidney. However, there was no increase in the expression of interferon-related genes (IFN-α/β, IFN-γ, Mx, and ISG15). Additionally, recombinant PoCCL34 induced high lysozyme activity in the serum of the flounder. These results indicate that although PoCCL34 is not involved in the antiviral response, it may play a significant role in the overall immune response of the flounder, particularly in mediating the inflammatory response.

The Antioxidant Role of a Taurine-Enriched Diet in Combating the Immunotoxic and Inflammatory Effects of Pyrethroids and/or Carbamates in Oreochromis niloticus

Simple Summary

Insecticidal pollution of surface waters is known to hurt the growth, survival, and breeding of aquatic animals. Different types of insecticides are known to be toxic to different aquatic organisms, particularly to fish species. In different types of wastewater, the fishes get exposed to different mixtures of insecticides. The current study hypothesized that co-exposure to lambda-cyhalothrin (LCT) and methomyl (MTM) insecticides might be more harmful due to duplicated effects than exposure to either one of them at a time. Oreochromis niloticus was the target fish in this study. The combative roles of taurine (TUR) against LCT and MTM exposures were evaluated. In the present work, exposure of O. niloticus to LCT and/or MTM exhibited adverse effects on immunological parameters, including leukocyte count, complement 3 concentration, antioxidant enzyme concentrations, and mRNA expression for cytokines (TNF-α and IL-1β) and chemokines (CC and CXC). This study also elucidated the more severe toxic effect of LCT than exposure to MTM in O. niloticus fish. The immune response and growth performance of O. niloticus showed marked improvements when provided a 1% TUR-enriched supplement.

Abstract

Indiscriminate use of insecticides is a major concern due to its ubiquitous occurrence and potential toxicity to aquatic animals. This study investigated the adverse effects of lambda-cyhalothrin (LCT; C₂₃H₁₉ClF₃NO₃) and methomyl (MTM; C₅H₁₀N₂O₂S) on immune system modulations and growth performance of juvenile fishes. The supportive role of a taurine (TUR; C₂H₇NO₃S)-supplemented diet was also evaluated. Juvenile O. niloticus fishes were exposed to LCT (0.079 µg/L), MTM (20.39 µg/L), or both in water and were fed on a basal diet only or taurine-supplemented basal diet. Exposure to LCT and MTM retarded growth and increased mortality rate. LCT and MTM reduced antioxidant enzyme activities (superoxide dismutase and glutathione peroxidase) and innate and humoral immunity but upregulated interleukin and chemokine expressions. Moreover, exposure to LCT and MTM elevated 8-OHdG levels and increased the mortality of Oreochromis niloticus after the experimental bacterial challenge. The TUR-enriched diet enhanced antioxidant enzymes and acted as a growth promoter and anti-inflammatory agent. TUR can modify innate and adaptive immune responses. Furthermore, TUR supplementation is a beneficial additive candidate for mitigating LCT and MTM toxicities mixed with O. niloticus aquafeed.