Demonstration of the immunogenicity of hepatitis B core antigen in a hepatitis B e antigen polypeptide (P19)

The core of Dane particles, the presently accepted hepatitis B virus nucleocapsid, contains two polypeptides (P19 and P45) with the antigenicity of hepatitis B e antigen (HBeAg). The antigenicity of hepatitis B core antigen (HBcAg) was not detectable in either of them by the conventional in vitro assay methods, despite the fact that both of these polypeptides were derived from the core of Dane particles. When a rabbit had been immunized with the purified preparation of P19 emulsified in complete Freund's adjuvant, however, humoral antibody against HBcAg was produced in addition to the antibody against HBeAg. Amino acid analysis of P19 disclosed a high content of arginine (12.9%), leucine (11.9%), serine (10.3%) and proline (10.2%). The amino acid composition of P19 was found to be strikingly similar to the composition of the 183 amino acid sequence deduced from the sequence of hepatitis B virus DNA which has been presumed to be encoding HBcAg. We conclude that both HBeAg and HBcAg are antigenic determinants borne by the major polypeptide (P19) constituting the core of Dane particles.