Current research on the immunostimulatory effects of CpG oligodeoxynucleotides in fish

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides within the context of certain flanking bases (CpG motifs) have been shown to induce potent innate and adaptive immune responses. Recognition of CpG motifs by the innate immune system requires engagement of toll-like receptor 9 (TLR-9), a newly identified member of toll-like receptor family, which induces cell signaling and subsequently triggers an immune response. The binding CpG-ODN to its specific membrane receptor and subsequently triggering of CpG-related signaling occurred within acidified endosomes. CpG-ODNs are being harnessed for a variety of therapeutic uses, including as immune adjuvants, for cancer therapy, as anti-allergens, and as immunoprotective agents. However, potential applications for immunostimulatory CpG-ODN in fish are just being explored. This article reviews recent progress in understanding the immunostimulatory effects of CpG DNA in fish.