Hepatitis B virus large surface protein is not secreted but is immunogenic when selectively expressed by recombinant vaccinia virus
Cheng KC., Smith GL., Moss B.
The envelope region of the hepatitis B virus (HBV) genome contains an open reading frame that begins upstream of the major surface protein gene. The two minor proteins that are initiated within this pre-s segment are immunogenic and may be involved in virus attachment to hepatocytes. We have constructed a recombinant vaccinia virus that contains the predicted coding segment for the large surface protein (LS) under control of a vaccinia virus that contains the predicted coding segment for the large surface protein (LS) under control of a vaccinia virus promoter. Cells infected with the recombinant virus synthesized HBV polypeptides of 39 and 42 kilodaltons, corresponding to the unglycosylated and glycosylated forms of LS, respectively. The presence of pre-s epitopes in the 39- and 42-kilodalton polypeptides was demonstrated by binding of antibody prepared against a synthetic peptide. Synthesis of the 42-kilodalton species was specifically inhibited by tunicamycin, suggesting that it is N-glycosylated. Despite apparent glycosylation, LS was not secreted into the medium of infected cells. Nevertheless, rabbits vaccinated with the purified recombinant virus made antibodies that recognized s and pre-s epitopes. Antibody to the NH2 terminus of LS appeared before or simultaneously with antibody that bound to the major surface protein. The additional immunogenicity provided by expression of LS may be advantageous for the development of an HBV vaccine.