Antigenic and immunogenic properties of a hepatitis A virus capsid protein expressed in Escherichia coli.

We have constructed a recombinant plasmid producing, in bacteria, a hepatitis A virus (HAV) capsid protein that may be useful as a subunit vaccine. HAV VP1 coding sequences were fused in-frame to NH2-terminal Escherichia coli TrpE coding sequences under the control of the tryptophan promoter. In the absence of exogenous tryptophan, E. coli containing this recombinant plasmid produced high levels of an 88-kilodalton fusion protein that was recognized in immunoblots by antibodies to TrpE and HAV. The TrpE/HAV VP1 protein was gel-purified and used to immunize rabbits. The resulting antiserum reacted with denatured HAV VP1 in immunoblots but did not react with intact virus. However, subsequent inoculation of an immunized animal with a subimmunogenic dose of inactivated, whole HAV resulted in the rapid appearance of a stable, virus-neutralizing antibody response.