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J. Virol., Jan 1998, 84-94, Vol 72, No. 1
M Triyatni, AR Jilbert, M Qiao, DS Miller and CJ Burrell
The efficacy of DNA vaccines encoding the duck hepatitis B virus (DHBV)
pre-S/S and S proteins were tested in Pekin ducks. Plasmid pcDNA I/Amp DNA
containing the DHBV pre-S/S or S genes was injected intramuscularly three
times, at 3-week intervals. All pre-S/S and S-vaccinated ducks developed
total anti-DHBs and specific anti-S antibodies with similar titers reaching
1/10,000 to 1/50,000 and 1/2,500 to 1/4,000, respectively, after the third
vaccination. However, following virus challenge, significant differences in
the rate of virus removal from the bloodstream and the presence of virus
replication in the liver were found between the groups. In three of four
S-vaccinated ducks, 90% of the inoculum was removed between <5 and 15
min postchallenge (p.c.) and no virus replication was detected in the liver
at 4 days p.c. In contrast, in all four pre-S/S-vaccinated ducks, 90% of
the inoculum was removed between 60 and 90 min p.c. and DHBsAg was detected
in 10 to 40% of hepatocytes. Anti-S serum abolished virus infectivity when
preincubated with DHBV before inoculation into 1-day-old ducklings and
primary duck hepatocyte cultures, while anti-pre-S/S serum showed very
limited capacity to neutralize virus infectivity in these two systems.
Thus, although both DNA vaccines induced high titers of anti-DHBs
antibodies, anti-S antibodies induced by the S-DNA construct were highly
effective in neutralizing virus infectivity while similar levels of anti-S
induced by the pre-S/S-DNA construct conferred only very limited
protection. This phenomenon requires further clarification, particularly in
light of the development of newer HBV vaccines containing pre-S proteins
and a possible discrepancy between anti-HBs titers and protective efficacy.
Copyright © 1998, American Society for Microbiology
Protective efficacy of DNA vaccines against duck hepatitis B virus infection
Department of Microbiology and Immunology, University of Adelaide, South Australia. mtryatni@microb.adelaide.edu.au
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