A Monoclonal Antibody Against the X Protein of Hepatitis B Virus: Fine Mapping of its Epitope and Application in a Quantitative ELISA of the X Protein in Sera of Hepatitis B Patients

A HBx-specific mouse monoclonal antibody was developed and its epitope mapped to a hydrophilic segment ⁹⁴HKRTLGL¹⁰⁰ using the multipin peptide synthesis technique. A sensitive ELISA with a threshold of 5 to 10 ng was developed to identify the HBx-positive hepatitis B cases and measure the levels of HBx in sera. The same patient sera were also analyzed for the presence of anti-HBx using the purified recombinant antigen. HBx was present in 23% of the cases (15/65) whereas only 14% of the cases (9/65) were positive for anti-HBx. The mean value of HBx in acute hepatitis sera was higher (522 ng/ml) than in cirrhosis cases (48 ng/ml). PCR amplification of the S gene showed that all 15 HBx-positive cases were also positive for the viral DNA.