Isolation and immunizations with hepatitis A viral structural proteins: induction of antiprotein, antiviral, and neutralizing responses.

An immune affinity purification procedure for hepatitis A virus (HAV) was designed which yielded milligram quantities of the virus with greater than 95% purity. The major structural proteins VP-1, VP-2, and VP-3 were isolated from the purified virus by electroelution from sodium dodecyl sulfate-polyacrylamide gels and used to immunize Lewis rats (three to four doses, 10 to 15 micrograms per dose). The two Lewis rats immunized with VP-1 developed a strong antibody response to VP-1, as determined by Western blot analysis and immune precipitation of the denatured protein. These animals also developed a good antibody response to the whole virus, as demonstrated by a positive response in a competitive radioimmunoassay (HAV antibody test) and by precipitation of the whole virus. In addition, both animals developed a low titer neutralizing antibody to HAV, as demonstrated by an in vitro cell culture assay. While the two rats receiving VP-2 developed only minimal responses to the protein and to the virus by the same assays described above, one of the two developed a significant neutralizing antibody to HAV. The immunization of one Lewis rat with VP-3 induced a good antibody response to both denatured protein and the whole virus. This serum sample was also demonstrated to neutralize the viral infectivity. Finally, two rabbits that had received inoculations of sodium dodecyl sulfate and heat-disrupted HAV (containing 20 to 30 micrograms of each protein per dose) developed good antiprotein responses to all of the proteins and good antiviral responses, including a consistently significant neutralizing activity. The neutralizing antibody responses suggest that the structural proteins of HAV, or a portion of them, could provide the basis for a subunit vaccine for HAV.