T-cells and CD45-cells discovery in the central nervous system of healthy and nodavirus-infected teleost fish Dicentrarchus labrax.

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.