Senegalese sole is susceptible to marine VHSV isolates but is not affected by freshwater isolates, which may indicate differences regarding virus-host immune system interaction. IFN I induces an antiviral state in fish, stimulating the expression of genes encoding antiviral proteins (ISG). In this study, the stimulation of the Senegalese sole IFN I by VHSV infections has been evaluated by the relative quantification of the transcription of several ISG (Mx, Isg15 and Pkr) after inoculation with marine (pathogenic) and freshwater (non-pathogenic) VHSV isolates. Compared to marine VHSV, lower levels of RNA of the freshwater VHSV induced transcription of ISG to similar levels, with the Isg15 showing the highest fold induction. The protective role of the IFN I system was evaluated in poly I:C-inoculated animals subsequently challenged with VHSV isolates. The cumulative mortality caused by the marine isolate in the control group was 68%, whereas in the poly I:C-stimulated group was 5%. The freshwater VHSV isolate did not cause any mortality. Furthermore, viral RNA fold change and viral titers were lower in animals from the poly I:C + VHSV groups than in the controls. The implication of the IFN I system in the protection observed was confirmed by the transcription of the ISG in animals from the poly I:C + VHSV groups. However, the marine VHSV isolate exerts a negative effect on the ISG transcription at 3 and 6 h post-inoculation (hpi), which is not observed for the freshwater isolate. This difference might be partly responsible for the virulence shown by the marine isolate.

The use of functional feeds in aquaculture is currently increasing. This study aimed to assess the combined impact of dietary green microalgae Chlorella fusca and ethanol-inactivated Vibrio proteolyticus DCF12.2 (CVP diet) on thick-lipped grey mullet (Chelon labrosus) juvenile fish. The effects on intestinal microbiota and the transcription of genes related to metabolism, stress, and the immune system were investigated after 90 days of feeding. Additionally, the fish were challenged with Aeromonas hydrophila and polyinosinic–polycytidylic acid (poly I:C) to evaluate the immune response. Microbiota analysis revealed no significant differences in alpha and beta diversity between the anterior and posterior intestinal sections of fish fed the control (CT) and CVP diets. The dominant genera varied between the groups; Pseudomonas and Brevinema were most abundant in the CVP group, whereas Brevinema, Cetobacterium, and Pseudomonas were predominant in the CT group. However, microbial functionality remained unaltered. Gene expression analysis indicated notable changes in hif3α, mhcII, abcb1, mx, and tnfα genes in different fish organs on the CVP diet. In the head kidney, gene expression variations were observed following challenges with A. hydrophila or poly I:C, with higher peak values seen in fish injected with poly I:C. Moreover, c3 mRNA levels were significantly up-regulated in the CVP group 72 h post-A. hydrophila challenge. To conclude, incorporating C. fusca with V. proteolyticus in C. labrosus diet affected the microbial species composition in the intestine while preserving its functionality. In terms of gene expression, the combined diet effectively regulated the transcription of stress and immune-related genes, suggesting potential enhancement of fish resistance against stress and infections.

To achieve insights in antiviral immune defense of the central nervous system (CNS), we investigated T cells and CD45 cells in the marine fish model Dicentrarchus labrax infected with the CNS-tropic virus betanodavirus. By employing markers for pan-T cells (mAb DLT15) and CD45-cells (mAb DLT22) in immunofluorescence (IIF) of leukocytes from brain, we obtained 3,7±2.3% of T cells and 7.3±3.2% of CD45⁺ cells. Both IIF and immunoelectron microscopy confirmed a leukocyte/glial morphology for the immunoreactive cells. Quantitative immunohistochemistry (qIHC) of brain/eye sections showed 1.9±0.8% of T⁺ cells and 2±0.9% of CD45⁺ cells in the brain and 3.6±1.9% and 4.1±2.2% in the eye, respectively. After in vivo RGNNV infection the number of T cells⁺/CD45 leukocytes in the brain increased to 8.3±2.1% and 11.6±4.4% (by IIF) and 26.1±3.4% and 45.6±5.9% (by qIHC), respectively. In the eye we counted after infection 8.5±4.4% of T cells and 10.2±5.8% of CD45 cells. Gene transcription analysis of brain mRNA revealed a strong increase of gene transcripts coding for: antiviral proteins Mx and ISG-12; T-cell related CD3ε/δ, TcRβ, CD4, CD8α, CD45; and for immuno-modulatory cytokines TNFα, IL-2, IL-10. A RAG-1 gene product was also present and upregulated, suggesting somatic recombination in the fish brain. Similar transcription data were obtained in the eye, albeit with differences. Our findings provide first evidence for a recruitment and involvement of T cells and CD45⁺ leukocytes in the fish eye-brain axis during antiviral responses and suggest similarities in the CNS immune defense across evolutionary distant vertebrates.

Background/Objectives: This study explores the bioactive potential of Bovistella utriformis biomass and its polysaccharides (PsBu) through comprehensive biochemical and bioactivity analyses, focusing on their antioxidant, cytotoxic, and antihyperglycemic properties. Methods: Elemental analysis determined the biomass’s chemical composition. Antioxidant activity was assessed using ABTS and DPPH assays. Monosaccharide composition was analyzed via gas chromatography-mass spectrometry (GC-MS). In vitro cytotoxicity assays were conducted on cancer and normal cell lines to determine IC₅₀ values and selectivity indices (SI). Zebrafish embryo toxicity was evaluated for teratogenic effects, and an in vivo antihyperglycemic study was performed in diabetic rat models. Results: The biomass exhibited high carbon content (around 41%) and nitrogen levels, with a balanced C/N ratio nearing 5. Protein content exceeded 50%, alongside significant carbohydrate, fiber, and ash levels. Antioxidant assays revealed inhibition rates of approximately 89% (ABTS) and 64% (DPPH). GC-MS analysis identified glucose as the predominant sugar (>80%), followed by galactose and mannose. Additionally, HPLC detected a photoprotective compound, potentially a mycosporin-like amino acid. Cytotoxicity assays demonstrated PsBu’s selective activity against colon, lung, and melanoma cancer cell lines (IC₅₀: 100–500 µg·mL⁻¹), while effects on normal cell lines were lower (IC₅₀ > 1300 µg·mL⁻¹ for HaCaT, >2500 µg·mL⁻¹ for HGF-1), with SI values approaching 27, supporting PsBu’s potential as a targeted anticancer agent. Zebrafish embryo assays yielded LC₅₀ values ranging from 1.4 to 1.8 mg·mL⁻¹. In vivo, PsBu reduced fasting blood glucose levels in hyperglycemic rats (approximately 210 mg·dL⁻¹ vs. 230 mg·dL⁻¹ in controls) and preserved pancreatic β-cell integrity (around 80% vs. 65% in controls). Conclusions: These findings suggest that B. utriformis biomass and PsBu exhibit strong antioxidant activity, selective cytotoxicity against cancer cells, and antihyperglycemic potential, making them promising candidates for further biomedical applications.

Gilthead sea bream and European sea bass display different resistance–susceptibility patterns during infection with different nervous necrosis virus (NNV) species, which may derive from differences in the triggered immune response. Based on this premise, we analysed the transcription of several selected immune-related genes in sea bream experimentally infected with NNV isolates obtained from sea bass (DlNNV, RGNNV) or sea bream (SaNNV, RGNNV/SJNNV). Viral replication only occurred in SaNNV-inoculated fish; therefore, the differences between the immune response elicited by both viruses may be the key to understanding the mechanism behind the inhibition of DlNNV replication. Principal component analysis clustered samples according to the viral isolate from 1 day post infection onwards and evidenced differences in the immune response against both viruses, even though no mortalities or symptoms were recorded. The response against DlNNV is characterized by higher rtp3 transcription early after the infection, longer-lasting il-10 transcription and stronger induction of casp1 and hsp70. These genes should be targets for future studies in order to elucidate their role in hampering NNV replication in sea bream, which is essential for developing effective prophylactic measures.