CpG oligodeoxynucleotides and plasmid DNA stimulate Atlantic salmon (Salmosalar L.) leucocytes to produce supernatants with antiviral activity

Unmethylated CpG dinucleotides are more frequent in the genomes of bacteria and viruses than of vertebrates. We report herein that plasmid DNA and syn thetic oliogodeoxynucleotides (ODNs) containing unmethylated CpG induce pro duction of antiviral cytokine activity in Atlantic salmon leucocytes, where as ODNs with an inverted motif (GpC) or with methylated cytosines have near ly no stimulatory effect. The adherent cell population, representing mainly macrophages, is directly activated by CpG-ODN, while the effect on the non -adherent population is weak. Since the peak antiviral activity in ODN-stim ulated leucocytes is seen after 48 h, this might indicate that the unmethyl ated DNA stimulates the adherent cells to produce co-stimulatory molecules, which in turn stimulates production of antiviral cytokines in the non-adhe rent cell population. The potent immune activation by CpG ODNs points to po ssible new applications as adjuvant in fish vaccines. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.