T-Cell Recognition of Pre-S Regions of HBsAg can Bypass Nonresponse to the S Region
The specific serologic marker of hepatitis B virus (HBV) infection is the hepatitis B surface antigen (HBsAg), which is present both in the intact virion and as free circulating filamentous and spherical 22-nm particles. The HBsAg is composed of a major polypeptide, p25, and its glycosylated form, gp28. However, additional polypeptides of higher m.w. (p39/gp42 and gp33/gp36) have been identified associated preferentially with the intact virion and the filamentous form of 22-nm particles (1). The p25 polypeptide is encoded by the S gene beginning from the third possible translational initiation site of a larger open reading frame (ORF) and is preceded in phase by 174 codons (adw subtype) designated the pre-S region (2). The large ORF for HBsAg terminates in a single stop codon but can initiate at three possible translational start codons, which define the pre-S(1), pre-S(2), and S regions, yielding p39, p33, and p25, respectively. All three polypeptides share the 226 amino acid residues of the S region (p25); p33 consists of the p25 sequence plus an amino-terminal 55 residues [pre-S(2)] (3) and p39 consists of the p33 sequence plus an amino-terminal 119 residues [pre-S(1)] (1) (see Fig. 1). Therefore, three different envelope polypeptides are expressed by the variable use of initiation codons in one ORF, and HBsAg-containing virions or particles may vary in composition relative to these three polypeptides. Herein, we designate purified HBsAg particle preparations by virtue of the highest m.w. polypeptide present (i.e. HBsAg/p39, HBsAg/p33, and HBsAg/p25).
KeywordsAntibody Binding Site Cell Proliferative Response Intact Virion Large Open Reading Frame Murine Strain
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