In vivo oral administration effects of various oligodeoxynucleotides containing synthetic immunostimulatory motifs in the immune response to pseudorabies attenuated virus vaccine in newborn piglets

Numerous studies have demonstrated that oligonucleotides containing CpG motifs (CpG ODN) are efficient immunoadjuvants to various antigens administered by parenteral routes to mice. Recently, it has been found that CpG ODNs also is a promising mucosal adjuvant in mice. To date, there have been no studies to screen the optimal CpG sequence and modified ODN backbone to piglets in vivo, when delivered by oral route. We have previously demonstrated that human-specific CpG ODN is a potent adjuvant to pseudorabies live attenuated virus (PRV) vaccine when administered subcutaneously (SC) or ocularly in piglets. In this study, we screened and evaluated the optimal CpG sequences (porcine-specific, human-specific, mouse-specific ODN) and optimal backbone (SOS-backbone consisting of a nuclease-resistant phosphorothioate guanosines at the 5' and the 3'-end and with a phosphodiester (O) in the center and phosphorothioate (S) backbone (S-backbone)) to PRV vaccine delivered orally in piglets. The proliferation of peripheral blood mononuclear cells (PBMCs), IFN-gamma and IL-4 in serum, and the titre of IgG, IgG2/IgG1 isotype in serum and IgA in intestinal washings and feces to PRV vaccine were tested at different time-points. The results suggested that, CpG ODNs augmented systemic (IgG in serum, T-cell proliferation) and mucosal (IgA in intestinal washings and feces) immune responses against antigen. CpG ODNs stimulated both T-helper type1 (Th1) (IgG2) and Th2 (IgA) responses when delivered orally. With the same backbone, the porcine-specific ODN-induced responses were comparable with human-specific ODNs, but stronger than mouse-specific CpG ODNs. SOS-backbone induced a stronger IFN-gamma and proliferative responses than S-backbone, while antibody responses induced by SOS-backbones were slightly less or similar with S-backbone. The in vivo data demonstrate for the first time that porcine-specific and human-specific ODNs both are optimal sequences for mucosal system in piglets.