CpG oligodeoxynucleotides activate grass carp (Ctenopharyngodon idellus) macrophages

In mice and humans, B cells, antigen-presenting cells including monocytes, macrophages and dendritic cells and natural killer cells can be stimulated directly or indirectly by the bacterial DNA and oligodeoxynucleotides (ODN) containing the CpG motifs (CpG DNA). Using head kidney macrophages of grass carp (Ctenopharyngodon idellus) as an in vitro model, we investigated the effects of several CpG-ODNs on fish immunocytes. The CpG-ODNs included the optimal motifs: the ODN-1826 (GACGTT) and -2006 (GTCGTT) for the mice and humans cells, the ODN-1670 (AACGTT) used in Atlantic salmon, the ODN-D containing two repeats motif of those in 1670 and the ODN-R with an inverted CpG. The results showed that CpG has an immunomodulatory role in grass carp, and all the ODNs except the ODN-R could activate macrophages, increasing the levels of superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)), acid phosphatase and bactericidal activity. New evidence was provided that CpG-ODN could induce the cell-mediated immunity in fish. Interestingly, no significant differences among the ODNs tested could be found and the ODN-D was not more efficient than 1670. It suggests that the sequence which contains the unmethylated 'CG' dinucleotides could make contribute to this immunostimulatory effect. These findings indicate that CpG-ODNs could be useful tools for understanding the important anti-bacterial defense mechanism in fish. And it may have potential application in the minimizing the impact of fish diseases and enhancing the efficacy of antigen and DNA vaccines.