Mapping of immunodominant B-cell epitopes and the human serum albumin-binding site in natural hepatitis B virus surface antigen of defined genosubtype

Twelve MAbs were generated by immunization of BALB/c mice with plasma-deriv ed hepatitis B virus surface spherical antigen particles subtype ayw2 (HBsA g/ayw2 genotype D). Their epitopes were mapped by analysis of reactivity wi th plasma-derived HBsAg/ayw2 and HBsAg/adw2 (genotype A) in enzyme immunoas says and blots. Mapping was supported by nested sets of truncated preS2 pro teins and preS2 peptides. Five antibodies were S domain-specific, seven wer e preS2-specific and 11 had a preference for genotype D. According to our d ata, group I of the three known epitope groups of preS2 has to be divided i nto IA and IB. Three preS2-specific MAbs forming the new group IA reacted w ith genotype D residues 3-15 which have not yet been described as an epitop e region. IA antibodies strongly inhibited the binding of polymerized human serum albumin. Two antibodies (group II) reacted with the glycosylated N-t erminal region of preS2 in plasma-derived HBsAg, but not with a preparation from transfected murine cells. One group III antibody was subtype-specific and reacted with the highly variable preS2 sequence 38-48. Only one antibo dy (group IB) mapped to the region (old group I) which was believed to be i mmunodominant and genotype-independent. Geno(sub)type-specific epitopes of preS2 are obviously the immunodominant components of natural HBsAg in BALB/ c mice, but these epitopes may be masked by serum albumins in humans. The d ata may explain why it is difficult to detect anti-preS2 antibodies in huma n recipients of preS2-containing vaccines, in spite of the preS2 immunodomi nance in mice.