Hepatitis B virus surface protein mutations clustered mainly in CTL immune epitopes in chronic carriers: results of an Iranian nationwide study

Abstract

Mutations within the coding region of hepatitis B surface antigen (HBsAg) have been found naturally in chronic carriers. To characterize the mutations of HBsAg from Iranian chronic carriers who were vaccine and/or medication naive. The surface genes from 360 patients were amplified and directly sequenced. The distribution of amino acid substitutions was classified according to different immune epitopes of the surface protein. All isolates belonged to genotype D. 222 (61.6%) of 360 patients contained at least one amino acid substitution. 404 (74.5%) of 542 amino acid changes occurred in different immune epitopes of HBsAg, of which 112 (27.7%) in 32 residues of B-cell epitopes (62 in the 'a' determinant); 111 (27.4%) in 32 residues of T helper; and 197 (48.7%) in 32 residues inside cytotoxic T lymphocyte (CTL) epitopes. One Th (186-197) and two CTL (28-51 and 206-215) epitopes were found to be hotspot motifs for the occurrence of 213 (52.7%) substitutions. 20 stop codons were identified in different epitopes. There was a significant association between amino acid substitutions and anti-HBe seropositivity; however, the correlation between such changes with viral load and ALT levels was not significant. In chronic hepatitis B virus(HBV) carriers, positive selection in particular outside the 'a' determinant appeared to exert influence on the surface proteins. These changes could be immune escape mutations naturally occurring due to the host immune surveillance especially at the T-cell level.

Naturally Occurring Surface Antigen Variants of Hepatitis B Virus in Tunisian Patients

“…This finding was in agreement with the results of other studies, especially in genotype D-infected patients [22,56]. In our study group, nearly half of the mutations (44.3%) occurred in the CTL epitope, suggesting a narrowly focused immune selection pressure at a hot spot position.…”

“…De Maddalena et al [13] reported a significantly higher intragenotypic distance in genotype D than genotypes A and G, especially at the ‘a' determinant. Thus, it can be suggested that what is already known about the higher affinity of genotype D for mutations in the pre-C region can also be true for other regions [22,23]. This hypothesis is reinforced by the results of our study.…”

“…Our study showed that the MHR is the more conserved region in the S gene, consistent with previous results showing that most occurrences of S mutations were in the region outside the MHR [22,40]. …”

Molecular identification of hepatitis B virus genotypes/subgenotypes: Revised classification hurdles and updated resolutions

“…Furthermore, analysing partial genes instead of the full-length genome can sometimes lead to false epidemiological signals from distant geographical regions. For instance, Khedive et al [56] analysed 681 bp of isolated strains from HBV carriers in Iran and reported five strains with HBV subgenotypes D5 and D8, which is inconsistent with the known geographical distribution of subgenotypes. According to all epidemiological studies from Iran, D1 is the most frequent subgenotype of HBV, followed by a minor population of D2.…”

A new vaccine escape mutant of hepatitis B virus causes occult infection

“…13 A majority of mutations of up-and downstream of MHR in different studies were found to be potentially responsible for vaccine breakthrough and HBsAg undetectability which unpredictably were found to be located within the known CTL epitopes of surface protein. 15,16 Mutations that abrogate recognition of a viral epitope by class Irestricted CTL contribute to viral persistence in a subset of patients with chronic HBV infection who express a narrow repertoire of anti-HBV CTL responses. Thus, viral mutations in CTL epitopes were able to evade cellular immunity and contribute to persistency.…”