Identification of CpG oligodeoxynucleotide sequences that induce IFN-γ production in canine peripheral blood mononuclear cells

Oligodeoxynucleotides containing the cytosine-phosphate-guanine (CpG) motif (CpG-ODNs) have been shown to induce TH1 immune responses in animals. Since the sequences of CpG-ODNs that induce TH1 responses are considered to vary among animal species, it is necessary to identify effective CpG-ODNs in each animal. In order to identify the sequences of CpG-ODNs that induce TH1 responses in dogs, mRNA expression and protein production of IFN-γ were examined in peripheral blood mononuclear cells (PBMCs) from healthy dogs treated with 11 kinds of synthetic CpG-ODNs. One of the 11 CpG-ODNs (No. 2 CpG-ODN, 5′-GGTGCATCGATGCAGGGGGG-3′) was shown to significantly increase mRNA expression and protein production of IFN-γ in canine PBMCs in a manner dependent on the sequence of the CpG motif. This CpG-ODN also enhanced the expression of IL-12 p40 mRNA in canine PBMCs, whereas expression of IL-12 p35, IL-18, and IL-4 mRNAs was not induced by this CpG-ODN. These results indicate that this CpG-ODN was able to produce IFN-γ by induction of TH1-skewed immune response in dogs. CpG-ODNs may be useful for inducing prophylactic and therapeutic immunity against allergic diseases, viral infection, and tumors in dogs.