HBsAg Mutants Clustered Mainly Outside of “a” Determinant in Chronic Carriers From Azarbayjan Province, Iran

Background: Hepatitis B virus (HBV) genetic and protein variations have been observed in chronic patients frequently. However, their role in the pathogenesis of chronicity has not been explored yet.

Objectives: The aims of this study were to determine the genotypes as well as the patterns of variations distribution in chronically infected patients from the north western part of Iran.

Materials and Methods: The surface genes from 17 chronic carriers were amplified, sequenced and subsequently aligned using international and national Iranian database.

Results: All strains belonged to genotype D, subgenotype D1 and subtype ayw2. Of all 56 “mutations” that occurred at 37 nucleotide positions, 25 (44.6%) were missense (amino acid altering) and 31 (55.4%) were silent (no amino acid changing) (S/M ratio: 1.2). At the amino acid level, 21 (91.3%) out of 23 amino acid mutations occurred in different immune epitopes within the surface proteins, of which 3 (14.3%) occurred in B cell, 8 (38%) in T helper and 10 (47.7%) inside CTL epitopes. In general, the association between amino acid mutations and especially, immune epitope substitutions was more significant in terms of HBeAg status than ALT levels in patients.

Conclusions: The distribution of amino acid mutations as well as the ratio between missense and silent nucleotide mutations (dN/dS) showed that a narrowly focused immune pressure had already been on the surface protein (especially CTL epitopes) which led to the emergence of escape mutants in these patients who were in tolerance phase of chronicity.