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A New Algorithm for Deduction of Hepatitis B Surface Antigen Subtype Determinants from the Amino Acid Sequence

Objective: We have reexamined hepatitis B virus subtypes to determine the role of specific HBsAg amino acids in serologic reactivity because of problematic genotype/subtype associations seen in a set of geographically diverse serum specimens. Methods: We obtained DNA sequences for 491 HBsAg-positive specimens from geographically distinct locations, determined their genotypes through phylogenetic analysis, and subtyped the specimens using an algorithm derived from published data on the molecular basis of HBsAg subtype reactivity. Problematic samples were subtyped serologically to resolve conflicts based on the amino acid sequence alone. Results: Three isolates were found to have unusual genotype/subtype associations. Examination of the isolates’ amino acid sequences suggested amino acid positions 122, 127, 140, 159 and 160 can be used to determine subtype reactivity from HBsAg amino acid sequences, while position 134, previously thought to play a role, is no longer important. Conclusions: This re-examination of hepatitis B virus subtypes shows the involvement of amino acid positions 122, 127, 140, 159 and 160 in HBsAg reactivity. While d, y, and r reactivities are controlled by single amino acid changes, w reactivity is determined by positions 122, 127, 140, and 159.