Mx expression in Atlantic salmon (Salmo salar L.) parr in response to Listonella anguillarum bacterin, lipopolysaccharide and chromosomal DNA

Mx genes are inducible by Type I interferons and are involved in antiviral defences. A commercially available vibrio bacterin, intended for immersion vaccination, was shown to be a potent inducer of Mx gene expression in Atlantic salmon parr following intraperitoneal injection. The response was dose and temperature dependent. At 10 °C and 10 times concentration the bacterin induced Mx response kinetics similar to that induced by poly I:C. °C, enhanced Mx responses were detected from days 1 to 9 with both 1 times (1×) and 10 times (10×) concentrated bacterin, with a tendency for a higher response to the concentrated bacterin on days 1 and 3. Basal levels of Mx mRNA were detected on day 12 after injection to both concentrations. The response induced by poly I:C was higher on day 1 and it was still present at day 12, with basal levels being reached on day 18. At 6 °C, there was a more definitive dose effect of the vibrio bacterin and the Mx response was delayed in comparison to that at 10 °C. Increased Mx expression did not appear until day 6 and with the 1× dose it had disappeared by day 9. However, the 10× dose continued to induce Mx at day 12, disappearing by day 18. response to the purified Listonella anguillarum lipopolysaccharide (LPS) and DNA in fish held at 10 °C showed some differences in the rate of onset. The response to DNA was faster, beginning on day 1 compared with day 3 for the LPS. The response to DNA peaked on day 3 while for LPS the peak was on day 9. However, the response to both components had disappeared by day 12. The response kinetics to the L. anguillarum DNA was essentially similar to the 10× dose of the vibrio bacterin and to poly I:C at 10 °C.