Antibody Responses of Mice Immunized with HA DNA Vaccines

Neutralization of influenza virus to prevent infection requires antibodies to the HA molecule. The ability of the HA-DNA vaccines to induce antibody production needs to be considered. If antibodies to HA are produced, hemagglutination would be inhibited. Why? The antibodies will bind to the hemagglutinin, thus preventing the binding of red blood cells to the HA (hemagglutination)

Methods

In all previous experiments, serum samples were collected prebooster, pre- and postchallenge for serum antibody analysis. Both HA and Hemagglutination inhibition (HI) assays were performed using 0.5% chicken RBC's. The HI titers are the reciprocal of the highest serum dilution giving complete inhibition of hemagglutination.

Results

Figure A. HI antibody titers of mice immunized with pHKHA prior to challenge with virus	Figure D. HI antibody titers of mice immunized with pTyIrHA and challenged with HK97.
Figure B. HI antibody titers of mice immunized with pHKHA and challenged with HK97	Figure C. HI antibody titers of mice immunized with pHKHA and challenged with CkHK97

Questions to Ponder

• What is the purpose of the data in figure A? answer Figure A shows that in 40% of immunized mice, low levels of HI antibodies are observed. This information is necessary for comparison with responses due to viral challenge. It serves as a 'baseline' response.
• Figure B shows low levels of HI antibodies in 40-50% of the animals. It was also found that 25% of the mice exhibited virus shedding. What does this suggest? answer the small number of animals with an antibody response suggests that this response is due to virus replication
• How can you explain the HI titers if mice challenged with CkHK97 being overall slightly higher that those of HK97-challenged mice? answer This is most likely due to the larger number of virus infectious units of the challenge dose of CkHK97. The 50% lethal dose of CkHK97 virus contains 100 times more infectious units than that of HK97.
• How does the antibody response of those immunized with pTyIrHA compare to those of mice immunized with pHKHA? answer Mice immunized with pTyIrHA showed high levels of postchallenge antibodies to both HK97 and CkHK97. This could be due to the replication of large amounts of virus in the lungs. If you remember, pTyIrHA was found to protect against death, but not against infection, thus many more virus particles would be permitted to replicate in pTyIrHA immunized mice than in pHKHA immunized mice.

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