Viral and host determinants in hepatitis B

Abstract

The outcome of hepatitis B infection is highly variable, ranging from acute disease resulting in the elimination of infection to persistent infection that can lead to cirrhosis or hepatocellular carcinoma. The factors determining the outcome in an individual are not fully known but may be classified into viral and host factors.

Frequencies of hemochromatosis gene mutations were assessed in 75 Iranian subjects with chronic hepatitis B infection. The major C282Y mutation was significantly more frequent in subjects infected with hepatitis B virus (HBV) (4%) than in 194 control subjects (0%, P=0.02). Our results reports, for the first time, a higher prevalence of C282Y mutation in a group of HBsAg positive patients comparing to healthy individuals and may support the role of the major HFE mutation (C282Y) in increasing the likelihood of development of liver disease in individuals with chronic HBV infection.

To clarify the role of viral factors in the clinical variability of chronic hepatitis B the precore and core promoter regions of HBV strains were characterized from 30 patients with HBeAg negative chronic hepatitis B (e-CHB) and 42 anti-HBe positive asymptomatic carriers (ASCs). G1896A precore stop mutants, detected in 77% of e-CHB patients and in 85% of ASCs, showed no association with viral load or aminotransferase levels. 20% of e-CHB patients and 31 % of ASCs harbored T1762 A1764 promotor mutants. These mutants in association with G1757 were linked to higher viral load in the patients, than those associated with A1757, 105.2+1.8 VS 103.2+0.8 copies/ml (P=0.004). Interestingly, the most common BCP mutations were T1764 G1766 double mutants, which were present in 33% of e-CHB patients and in 29% of ASCs.

The T1764 G1766 double mutant was only present in strains with A 1717 (p<0 .001), which is more frequent in genotype D strains than in strains belonging to other genotypes. On the other hand, the T1762 A1764 double mutation was more frequently found in association with G1757 than A1757 Thus position 1757 affects the emergence of promoter double mutants and would predict a relative genotypic restriction of both the T1762 A1764 and the T1764 G1766 double mutants.

To investigate the role of mutations in different immune epitopes of hepatitis B core antigen (HBcAg) in HBeAg negative chronic hepatitis B (eCHB), amino acid 1-150 of HBcAg were characterized for HBV strains from 29 patients and 48 ASCs from Iran. Amino acid substitutions were found to cluster in eight different regions: residues 21-27, 35-40, 49-59, 6470, 77-87, 91-95, 105-116, and 130-135 of HBcAg. Residue 21, in an HLA-A2 CD8 epitope, was the most variable amino acid.

Region 64-70, which is known to form part of a CD4 T cell epitope, was found to be the most variable region often with a Glu64Asp substitution. This was associated with other amino acid substitutions at positions 51-97 (P<0.001). An inverse relation was found between viral load and mutations in the region 18-27 and none of the patients with these mutants had a viral load > 106 viral particles ml-1 (p<0.0001). It is possible that CTLs of patients with higher viral load could be exhausted because of this load and there are fewer mutations in CTL epitope of isolates of patients with higher viral load comparing to patients harboring isolates with lower replication reflecting a more vigorous CTL response and thereby a milder state of disease in the ASCs. Core promoter mutations that occur in initial phase of seroconversion might temporarily increase viral load with specific CTL exhaustion as a consequence in some infected individuals.