CRISPR/Cas9-induced knockout of tumor necrosis factor-alpha-type I augments viral infection in zebrafish.

Tumor necrosis factor-alpha (TNF-α) is a pleiotropic cytokine with critical roles in inflammation, cell survival, and defense. As a member of the TNF superfamily, it exerts its effects by binding to transmembrane receptors and triggering various downstream signaling pathways. Although TNF-α's involvement in antiviral responses in mammals is well-established, its role in teleost remains poorly understood. This study investigated the contribution of TNF-α1 to antiviral immunity in zebrafish using a tnf-α1 knockout (KO) line. We challenged both wild-type and tnf-α1 zebrafish with viral hemorrhagic septicemia virus (VHSV) at both embryonic and adult stages. Mortality was observed at 4 days post-infection (dpi) in tnf-α1-deficient adult fish challenged with 5 × 10 TCID (VHSV) and at 5 dpi in adult wild fish challenged with the same concentration. In addition, tnf-α1 KO adult fish reached the maximum mortality of 100 % at 20 dpi, whereas wild adult fish reached 54 % mortality at the same time point. This increased susceptibility to early mortality was associated with a higher viral burden and altered expression of key immune genes, including the pro-inflammatory cytokines il-6 and il-1β, the anti-inflammatory cytokine il-10, and interferon-related genes such as irf1 and ifn-γ. Our findings demonstrate the crucial role of TNF-α1 in antiviral defense mechanisms in zebrafish and provide valuable insights into the functional conservation of TNF-α signaling across vertebrate species. This knowledge may contribute to the development of strategies to combat viral diseases in fish.