Immunoprotection induced by CpG-ODN/Poly(I:C) combined with recombinant gp90 protein in chickens against reticuloendotheliosis virus infection
The present study is focused on investigating the immunoprotective effects of CpG-ODN/Poly(I:C) combined with the viral glycoprotein gp90 protein against reticuloendotheliosis virus (REV) infection in chickens. REV's gp90 gene was amplified from the REV-infected cells and expressed in Escherichia coli (E.coli). The expressed products, upon purification, were inoculated into 7-day-old chickens with PBS, CpG-ODN or Poly(I:C) adjuvant; Two booster inoculations were then conducted, and then each chicken was challenged. The presence of REV-antibodies in serum was determined weekly after the first vaccination. The viremia and immunosuppressive effects of REV infection were also monitored after the challenge. The neutralizing effects of the antisera were tested in vitro. The results showed that the recombinant gene containing REV gp90 gene was expressed into the recombinant protein with a size of 51 Kilo Dalton (KD), which could be recognized by a monoclonal antibody (MAb) against the gp90 protein. The viremia and immunosuppressive effects of avian influenza virus (AIV) vaccine caused by REV challenge in CpG-ODN group and in Poly(I:C) group were dramatically decreased. REV antibody with low titers was induced in gp90 group and the inoculated chickens were partly protected. Compared with those in gp90 group, the titers and the positive ratios of REV antibody in CpG+gp90 group were significantly increased, whereas the viremia and immunosuppressive effects of AIV vaccine caused by REV infection were significantly decreased. In the Poly(I:C) +gp90 group, the viremia and immunosuppressive effects caused by REV infection were also dramatically decreased, although REV antibody responses were softly increased. The diluted antisera from the vaccinated chickens in both groups could completely inhibit the replication of REV in chick fibroblast cells (CEF). Hence, it can be concluded that CpG-ODN or the Poly(I:C) adjuvant can enhance the antiviral effects of the REV subunit vaccine against REV infection, which may result from different mechanisms.