The immunosuppressive effects of continuous CpG ODNs stimulation in chinese mitten crab, Eriocheir sinensis

CpG oligodeoxynucleotides (CpG ODNs) have been widely used as a novel vaccine adjuvant inmammals due to its immune protection, long effectiveness and safety. In the present study, thelong-term immune effects as well as immunosuppression of CpG ODNs was evaluated by comparing the immune parameters of Chinese mitten crab, Eriocheir sinensis after continuous or interval feeding with CpG ODNs-supplement diet for 21 days (designated as CC and CI group, respectively). In the CI group, the mRNA transcripts of EsTolls (EsToll1 and EsToll2) and EsMyD88 (adaptor molecule) in hepatopancreas maintained at a significantly higher level (p < 0.05) compared with the CC group after 7 days and 14 days feeding, while there was no significant difference between them at the 21st day. Moreover, after a significant increase at 7th day, the expression level of EsLITAF mRNA [Lipopolysaccharide-induced tumor necrosis factor (TNF)-α] in CC group decreased at 14th-21st day, while that in CI group kept increasing at 14th day, followed by a decrease at 21st day. The TNF-α in plasma of CC group was abnormally increased at the 21st day (p < 0.05) in CC group compared with the significant raise at 7th-14th in CI group. Moreover, the phagocytic activity and reactive oxygens (ROS) level of hemocytes in continuous CpG ODNs feeding crabs were significantly lower than those in interval feeding crabs. These results indicated that long-term and continuous CpG ODNs stimulation could reduce the activation of pro-inflammatory cytokine production, hemocyte phagocytosis and ROS generation, displaying immunosuppressive effects on the immune system of crabs.