Nanoplastics Increase Fish Susceptibility to Nodavirus Infection and Reduce Antiviral Immune Responses

Nanoplastics (NPs) might cause different negative effects on aquatic organisms at different biological levels, ranging from single cells to whole organisms, including cytotoxicity, reproduction, behavior or oxidative stress. However, the impact of NPs on disease resistance is almost unknown. The objective of this study was to assess whether exposure to 50 nm functionalized polystyrene NPs impacts fish susceptibility to viral diseases both in vitro and in vivo. In particular, we focused on the nervous necrosis virus (NNV), which affects many fish species, producing viral encephalopathy and retinopathy (VER), and causes great economic losses in marine aquaculture. In vitro and in vivo approaches were used. A brain cell line (SaB-1) was exposed to 1 μg mL⁻¹ of functionalized polystyrene NPs (PS-NH₂, PS-COOH) and then infected with NNV. Viral titers were increased in NP-exposed cells whilst the transcription of inflammatory and antiviral markers was lowered when compared to those cells only infected with NNV. In addition, European sea bass (Dicentrarchus labrax) juveniles were intraperitoneally injected with the same NPs and then challenged with NNV. Our results indicated that NPs increased the viral replication and clinical signs under which the fish died although the cumulate mortality was unaltered. Again, exposure to NPs produced a lowered inflammatory and antiviral response. Our results highlight that the presence of NPs might impact the infection process of NNV and fish resistance to the disease, posing an additional risk to marine organisms.

Identification and Regulation of Interleukin-17 (IL-17) Family Ligands in the Teleost Fish European Sea Bass

Interleukin-17 (IL-17) cytokine comprises a family of six ligands in mammals with proinflammatory functions, having an important role in autoimmune disorders and against bacterial, viral, and fungal pathogens. While IL-17A and IL-17F ligands are mainly produced by Th cells (Th17 cells), the rest of the ligands are expressed by other immune and non-immune cells and have different functions. The identification of IL-17 ligands in fish has revealed the presence of six members, counterparts to mammalian ones, and a teleost-specific form, the fish IL-17N. However, tissue distribution, the regulation of gene expression, and scarce bioactivity assays point to similar functions compared to mammalian ones, though this yet to be investigated and confirmed. Thus, we have identified seven IL-17 ligands in the teleost European sea bass (Dicentrarchus labrax), for the first time, corresponding to IL-17A/F1, IL-17A/F2, IL-17A/F3, IL-17C1, IL-17C2, IL-17D, and IL-17N, according to the predicted protein sequences and phylogenetic analysis. They are constitutively and widely transcribed in sea bass tissues, with some of them being mainly expressed in the thymus, brain or intestine. Upon in vitro stimulation of head-kidney leucocytes, the mRNA levels of all sea bass IL-17 ligands were up-regulated by phytohemagglutinin treatment, a well-known T cell mitogen, suggesting a major expression in T lymphocytes. By contrast, the infection of sea bass juveniles with nodavirus (NNV), a very pathogenic virus for this fish species, resulted in the up-regulation of the transcription of IL-17C1 in the head-kidney and of IL-17C1 and IL-17D in the brain, the target tissue for NNV replication. By contrast, NNV infection led to a down-regulated transcription of IL-17A/F1, IL-17A/F2, IL-17C1, IL-17C2, and IL-17D in the head-kidney and of IL-17A/F1 and IL-17A/F3 in the brain. The data are discussed accordingly with the IL-17 ligand expression and the immune response under the different situations tested.