| Summary: | The overexpression of <i>GATA-3</i>, <i>T-bet</i> and <i>TGF-ß</i> may theoretically induce <i>IL-4/A</i>, <i>IFN-γ</i> and <i>IL-17A</i> expression, respectively. Whether this also applies to fish is not yet known. The plasmid vectors encoding reporter gene (RFP)-tagged <i>T-bet</i>, <i>GATA-3</i> and <i>TGF-ß</i> were used as overexpression tools, transfected into cells or injected intramuscularly to monitor the expression of <i>IFN-γ</i>, <i>IL-4/13A</i> and <i>IL-17A</i>. In addition, the fish were either experimentally challenged with <i>Vibrio anguillarum</i> (VA group) or <i>Piscirickettsia salmonis</i> (PS group). The reporter gene (RFP) inserted upstream of the <i>GATA-3</i>, <i>T-bet</i> and <i>TGF-ß</i> genes, was observed in muscle cell nuclei and in inflammatory cells after intramuscular (i.m.) injection. PS group: following the injection of <i>GATA-3</i> and <i>T-bet</i>-encoding plasmids, the expression of <i>GATA-3</i> and <i>T-bet</i> was high at the injection site. The spleen expression of <i>IFN-γ</i>, following the injection of a <i>T-bet</i>-encoding plasmid, was significantly higher on day 2. VA group: The <i>T-bet</i> and <i>GATA-3</i>-overexpressing fish expressed high <i>T-bet</i> and <i>GATA-3</i> mRNA levels in the muscles and on day 4 post-challenge. The expression of <i>TGF-ß</i> in the muscles of fish injected with <i>TGF-ß</i>-encoding plasmids was significantly higher on days 7 (8 days pre-challenge) and 19 (4 days after challenge). The protective effects of the overexpression of <i>T-bet</i>, <i>GATA-3</i> and <i>TGF-ß</i> on both bacterial infections were negligible.
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