Coexistence of hepatitis B surface antigen (HBs Ag) and anti-HBs antibodies in chronic hepatitis B virus carriers: influence of "a" determinant variants

Abstract

In chronic hepatitis B (CHB), the persistence of hepatitis B surface antigen (HBs Ag) is sometimes associated with antibodies (Ab) to HBs (anti-HBs). To assess the hypothesis of the selection of HBs Ag immune escape variants in CHB patients, the variability of the HBV S gene was determined for patients persistently carrying both HBs Ag and anti-HBs antibodies and patients solely positive for HBs Ag. We selected 14 patients who presented both markers (group I) in several consecutive samples and 12 patients positive for HBs Ag only (group II). The HBs Ag-encoding gene was amplified and cloned, and at least 15 clones per patient were sequenced and analyzed. The number of residue changes within the S protein was 2.7 times more frequent for group I than for group II patients and occurred mostly in the "a" determinant of the major hydrophilic region (MHR), with 9.52 versus 2.43 changes per 100 residues (P = 0.009), respectively. Ten patients (71%) from group I, but only three (25%) from group II, presented at least two residue changes in the MHR. The most frequent changes in group I patients were located at positions s145, s129, s126, s144, and s123, as described for immune escape variants. In CHB patients, the coexistence of HBs Ag and anti-HBs Ab is associated with an increase of "a" determinant variability, suggesting a selection of HBV immune escape mutants during chronic carriage. The consequences of this selection process with regard to vaccine efficacy, diagnosis, and clinical evolution remain partially unknown.

FIG. 1.

Frequencies of residue substitutions within the S protein in isolates from HBs Ag/anti-HBs patients (group I) (black bars, n = 14) and solely HBs Ag-positive patients (gray bars, n = 12), analyzed in intervals of 10 amino acids each. Each bar represents the percentage of mutated residues for all clones at each interval of 10 amino acids per group. Residue changes linked to genotypic polymorphisms were not taken into account. The two overlapping frames of the S and polymerase proteins are represented at the bottom of the diagram.

FIG. 2.

Numbers of residue changes for group I and II patients within the “a” determinant of the MHR. The numbers for the 14 patients (black circles) in group I and the 12 patients (open circles) in group II are distributed according to the numbers of residue changes in the “a” determinant. Statistical significance was calculated using a Mann-Whitney test.