Résumé
Objective To explore the correlation between serum hepatitis B virus (HBV) X antigen/antibody (HBxAg-wild/HBxAb-wild,and HBxAg-mutant/HBxAb-mutant) and the disease progression in patients with chronic HBV infection.Methods A direct enzyme immunosorbent asssay (ELISA) was performed to detect HBxAb using recombinant antigen,and a double antibody sandwich ELISA assay to detect HBxAg using monoclonal antibody and specific rabbit polyclonal antibody.HBxAg-wild/HBxAb-wild and HBxAg-mutant/HBxAb-mutant were tested in sera from cases at different stages of chronic HBV infection.A chi-square test was employed to examine statistical significance.Results The positive rates of HBxAg-wild and HBxAg-mutant in the chronic asymptomatic HBV carriers,chronic hepatitis,hepatitis B-related cirrhosis and liver cancer were 6.2％ (2/32),10.7％ (3/28),28.6％ (6/21),43.6％ (17/39) and 3.1％ (1/32),10.7％ (3/28),33.3％ (7/21),48.7％ (19/39),respectively.The positive rates of HBxAb-wild and HBxAb-mutant in the above mentioned groups were 6.2％ (2/32),21.4％ (6/28),38.1％ (8/21),53.8％ (21/39)and 6.2％ (2/32),25.0％ (7/28),42.9％ (9/21),61.5％ (24/39) respectively.The positive rates of HBxAg-wild and HBxAg-mutant were not significantly different among the above groups (x2 =0.871,0.780,0.565 and 0.317,respectively; all P＞0.05) ; The positive rates of HBxAb-wild and HBxAb-mutant were also similar among all the groups (x2 =0.780,0.709,0.580 and 0.210,respectively; all P＞0.05).The positive rates of HBxAg-wild,HBxAb-wild,HBxAg-mutant,HBxAb-mutant in patients with low viral loads (HBV DNA＜1 × 104 copy/mL) were 36.5％ (23/63),44.4％ (28/63),42.9％ (27/63) and 54.0％ (34/63),respectively,those in patients with high viral loads (HBVDNA≥1×104 copy/mL) were 8.8％ (5/57),15.8％ (9/57),5.3％ (3/57) and 14.0％ (8/57),respectively.The positive rates of HBxAg and HBxAb were significantly higher in cases with low viral loads than those with high viral loads (x2 =12.869,11.522,22.556 and 20.976,respectively; all P＜0.05).The positive rates of HBxAg-wild,HBxAb-wild,HBxAg-mutant,HBxAb-mutant in the HBeAg positive group were 21.7％ (18/83),30.1％ (25/83),22.9％ (19/83) and 32.5％ (27/83),respectively,while those in the HBeAg negative group were 27.0％ (10/37),32.4％ (12/37),29.7％ (11/37) and 40.5％ (15/37),respectively.No significant difference of HBxAg/HBxAb positive rates between HBeAg positive group and HBeAg negative group was noticed (x2 =0.408,0.064,0.638 and 0.722,respectively; all P＞0.05).Conclusions The antigenicity and specificity of HBV X protein remains similar after the occurrence of A1762T/G1764A double mutant in X gene.It is also found that the positive rates of HBxAg and HBxAb increase with disease progression.HBxAg/HBxAb might be promoting factors for tumorigenesis in chronic HBV infection.HBxAg and HBxAb might have negative influence on HBV replication.
Résumé
To settle the foundation for the future research on the influence of wild and mutant (A1762T/ G1764A) HBV X gene on the progress of chronic HBV infection and hepatic tumorigenicity, wild and mutant (A1762T/G1764A) HBxAgs expression system was constructed. The wild and mutant (A1762T/ G1764A) HBV X genes were amplified with polymerase chain reaction (PCR) from HBV genome were inserted into pGEX-6P-2 and confirmed by sequencing respectively. Prokaryotic expression vectors pGEX-6P-2-hbvx(w) and pGEX-6P-2-hbvx(m) (A1762T/G1764A) were constructed and transformed to Trans1-blue; wild and mutant HBxAgs were expressed through IPTG induction respectively; after refolding of inclusion body, the wild and mutant HBxAgs were purified with GSTrap FF; and analysised by SDS-PAGE, Western blot and ELISA. SDS-PAGE analysis showed that the expression system was able to express target protein efficiently; the concentrations of purified wild HBxAg and mutant HBxAg were 4.88 mg/mL and 5.07 mg/mL respectively; Western blot analysis certified both the wild HBxAg and the mutant HBxAg could be recognized by the same monoclonal antibody against HBxAg; the two expressed fusion antigens coated in microtiter plate were able to react with the sera of HBV infected patients but not with the sera from healthy donors in ELISA. Results demonstrated that we successfully established a system for expression of hepatitis B x antigen and lay the foundation for further research on the role and molecular mechanisms of the mutant HBxAg in the progress of chronic HBV infection and hepatic tumorigenicity.