Abstract
BackgroundHepatitis B virus (HBV) is a small DNA-containing virus with 4 genes, C, S, X and P. The S gene codes for the surface antigen (HBsAg), which contains the "a" determinant, the main region for induction of a protective humoral immune response. To compare the genotype and sequence of the "a" determinant between strains isolated from asymptomatic and symptomatic Mexican HBV carriers.Results21 asymptomatic (blood donors) and 12 symptomatic (with clinical signs and with >1 year lamivudine treatment) HBV carriers were studied; all patients were positive for the HBsAg in serum. Viral load, genotypes, and subtypes were determined in plasma. A fragment of the S gene including the "a" determinant was PCR amplified and sequenced to determine genotype, subtype and to identify mutations. Mean viral load was 0.7965 × 104 copies/ml in asymptomatic carriers and 2.73 × 106 copies/ml in symptomatic patients. Genotypes H, C, and F were identified in asymptomatic individuals; whereas H was dominant in symptomatic patients. A fragment of 279 bp containing the "a" determinant was amplified from all 33 carriers and sequences aligned with S gene sequences in the GenBank. Mutations identified were Y100N, T126I, Q129H and N146K in the asymptomatic group, and F93I and A128V in the symptomatic group.ConclusionDifferences in genotype and in mutations in the "a" determinant were found between strains from asymptomatic and symptomatic HBV Mexican carriers.
Highlights
Hepatitis B virus (HBV) is a small DNA-containing virus with 4 genes, C, S, X and P
A higher diversity in the infecting genotypes was found among asymptomatic carriers (H, C, F, C/H, C/ F/H), than in symptomatic patients, where genotype H was found in all cases and in only one case a C/H infection was detected
These results would suggest that in our population, genotype H strains are more prevalent than C and F genotypes in symptomatic cases. This observation is relevant since studies indicate certain association of the genotype with the clinical outcome of the infection; in hepatocellular carcinoma, genotype C was more prevalent in patients >50 years and genotype B more prevalent in patients
Summary
Hepatitis B virus (HBV) is a small DNA-containing virus with 4 genes, C, S, X and P. The S gene codes for the surface antigen (HBsAg), which contains the "a" determinant, the main region for induction of a protective humoral immune response. The HBsAg contains the major epitopes for induction of a protective humoral immune response [2,3,4,5,6] These epitopes are localized in the region known as the "a" determinant, between amino acid residues 99 and 169 [710], and are involved in the binding of antibodies against HBsAg. Amino acids changes in this region render mutant strains able to escape immune responses induced by vaccines [5,6,11,12]. Immune-escape mutants occur naturally [13,14,15], and in strains from patients with a weak or negative HBsAg reactivity in detection assays [10,15]
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