Characterization of three distinct CpG oligonucleotide classes which differ in ability to induce IFN alpha/beta activity and cell proliferation in Atlantic salmon (Salmo salar L.) leukocytes.

Oligodeoxynucleotides (ODNs) containing unmethylated CpG dinucleotides within specific sequence contexts (CpG motifs) are in humans divided into three distinct classes (A, B and C). The CpG ODNs, like baterial DNA, are recognized by the vertebrate immune system and are known to stimulate immune responses. The characterization of the different classes is based on their structure and biological activity. In this study, we report the effects of these classes of CpG ODNs as they are defined in humans on IFN alpha/beta production and cell proliferation in Atlantic salmon spleen, head kidney and blood leukocytes. These studies revealed that CpG A together with CpG C are strong inducers of IFN alpha/beta in spleen and head kidney leukocytes, whilst CpG B and CpG C had the highest capacity to stimulate cell proliferation in all three cell populations. These findings are the first to establish that the effects of the different CpG classes are comparable between fish and man.