To observe the antibody responses induced by recombinant A subgroup avian leukosis virus (ALV-A) gp85
protein vaccine plus CpG-ODN adjuvant and the protection of maternal antibodies (MAbs) for the
hatched chickens against early infection, the gp85 gene was amplified from the proviral cDNA of ALVA-SDAU09C1
strain using PCR and the recombinant plasmid containing target gene was constructed
and expressed in Escherichia Coli. The expressed product was confirmed using SDS–PAGE and western
blot that it is about 46 KD of recombinant protein. The purified recombinant proteins combining with
CpG-ODN adjuvant or Freund’s adjuvant were inoculated into the breeder hens, the ALV-A antibodies
in serum and in egg-yolk were detected; the fertilized eggs from the vaccinated hens with different titers
of egg-yolk antibody were hatched and then challenged with 104.2/0.1 mL TCID50 of ALV-A-SDAU09C1
strain, all the hatched chickens were weekly detected for the viremias and the cloacal swab P27 antigen
and pathological lesions; the neutralizing test of antisera in vitro was conducted. The results showed that
the recombinant gp85 proteins combining with CpG-ODN adjuvant could induce the breeder hens to produce
better antibody responses than gp85 protein with Freund’s adjuvant or without adjuvant; the MAbs
with higher titers induced by CpG-ODN + gp85 proteins could obviously decrease the ratios of viremias
(13% vs 33%), cloacal detoxification (20% vs 67%) and death (0% vs 22%) caused by ALV-A infection than
those by gp85 protein without adjuvant. The results of the neutralizing test indicated that the antisera
from the hatched chickens could neutralize the ALV-A-SDAU09C1 strain in vitro, but which depends
on the antibody titers. The results of IFA confirmed that the serum antibody could combine with the
ALV in DF1 cells. It can be concluded that the prepared ALV-A gp85 subunit vaccine combining with
CpG-ODN adjuvant could induce the breeder hens to produce better neutralizing antibody responses
and protect 80% of their offspring chickens against early infection.