Abstract:
Influenza A virus causes infection in a variety of animal species including
humans. The first outbreak of avian influenza (H5N1) virus in a human occurred in
Hong Kong in 1997. As of Jan 2007, 270 cases of H5N1 infection in humans had
been reported by the World Health Organization with a fatality rate of 60%. The
recent outbreaks of avian influenza in humans have demonstrated the need for vaccine
development. Hemagglutinin (HA) and neuraminidase (NA), the envelope
glycoproteins of the virus, are attractive vaccine candidates as they are major
protective antigens and the process of production is safe. The study of the
immunogenicity of the recombinant hemagglutinin and neuraminidase proteins in this
study will provide useful information for further avian influenza vaccine development.
Recombinant envelope proteins H5N1, 63 kDa of rHA5 and 55 kDa of rNA1,
were successfully produced in prokaryotic system by using pBAD/His expression
vector. The immunogenicity of rHA5 and rNA1 recombinant proteins were assessed
in BALB/C mice. The antibody titer of 1:100 and 1:5 were chosen for use in
comparison of immune response in immunized mice determined by Enzyme-linked
Immunosorbent Assay (ELISA) and Indirect Immunofluorescence Assay (IFA),
respectively. The results demonstrated that rHA5 could induce significantly higher
immune response than rNA1 (p<0.05). The result of microneutralization assay
showed that the serum from both rHA5 and rNA1 immunized mice and showed low
neutralizing antibody response at titer 1:50.
This study showed that a specific antibody developed in animals immunized with
rHA5 and rNA1 recombinant proteins has potential in activating neutralizing antibody
and may be appropriate for further development of an avian influenza virus vaccine.
The immunogenicity of rHA5 and rNA1 recombinant proteins produced in eukaryotic
system and neutralizing epitope in these regions should be further studied. Moreover,
the strain of the virus used in vaccine development should be accurately predicted
because the neutralizing antibody has been reported to be subtype and strain specific.