High expression of small hepatitis D antigen in Escherichia coli and ELISA for diagnosis of hepatitis D virus

Hepatitis D virus (HDV) infection is often accompanied by hepatitis B virus (HBV) infection. Co-infection of HDV and HBV may lead to more severe symptoms and even death. Current methods for HDV diagnosis have high false-positive rates and show significant result discrepancies. The Abbott AxSYM AUSAB test, currently a standard test for HDV detection, is too laborious and expensive for routine application. Therefore, new sensitive and cost-efficient methods for HDV diagnosis are urgently needed. In this study, S-HDAg protein was produced in high yield in Escherichia coli. Optimal protein production was achieved by optimization of S-HDAg gene codons according to the codon preference of E. coli and using host cells with appropriate cell density. Under optimal expression conditions, the S-HDAg protein expression yield (30 mg/l) was the highest among any proteins expressed in E. coli. A standard enzyme-linked immunosorbent assay (ELISA) for HDV was developed using the purified S-HDAg protein, which showed high specificity against hepatitis B, C, D and E viruses. Overall, the ELISA had superior specificity and sensitivity compared with the Abbott AxSYM AUSAB test and was also more convenient and cost-efficient.