AIM:To elucidate the molecular mechanisms underlying hepatitis B virus(HBV)occult infection of genotype C.METHODS:A total of 10 types of hepatitis B surface antigen(HBs Ag)variants from a Korean occult cohort were used.After a complete HBV genome plasmid mutated such that it does not express HBs Ag and plasmid encoding,each HBs Ag variant was transiently co-transfected into Hu H-7 cells.The secretion capacity and intracellular expression of the HBV virions and HBs Ags in their respective variants were analyzed using real-time quantitative polymerase chain reaction assays and commercial HBs Ag enzyme-linked immunosorbent assays,respectively.RESULTS:All variants exhibited lower levels of HBs Ag secretion into the medium compared with the wild type.In particular,in eight of the ten variants,very low levels of HBs Ag secretion that were similar to the negative control were detected.In contrast,most variants(9/10)exhibited normal virion secretion capacities comparable with,or even higher than,the wild type.This provided new insight into the intrinsic nature of occult HBV infection,which leads to HBs Ag sero-negativeness but has horizontal infectivity.Furthermore,most variants generated higher reactive oxidative species production than the wild type.This finding provides potential links between occult HBV infection and liver disease progression.CONCLUSION:The presently obtained data indicate that deficiency in the secretion capacity of HBs Ag variants may have a pivotal function in the occult infections of HBV genotype C. AIM: To elucidate the molecular mechanisms underlying hepatitis B virus (HBV) occult infection of genotype C. METHODS: A total of 10 types of hepatitis B surface antigen (HBs Ag) variants from a Korean occult cohort were used. After a complete HBV genome plasmid mutated such that it does not express HBs Ag and plasmid encoding, each HBs Ag variant was transiently co-transfected into Hu H-7 cells. secretion capacity and intracellular expression of the HBV virions and HBs Ags in their respective variants were analyzed using real-time quantitative polymerase chain reaction assays and commercial HBsAg enzyme-linked immunosorbent assays, respectively.RESULTS: All variants exhibit lower levels of HBsAg secretion into the medium compared with the wild type.In particular, in eight of the ten variants, very low levels of HBs Ag secretion that were similar to the negative control were detected. In contrast, most variants (9/10) exhibits normal virion secretion capacities comparable with, or even higher th an, the wild type. this provided new insight into the intrinsic nature of occult HBV infection, which leads to HBs Ag sero-negativeness but has horizontal infectivity .Furthermore, most variants generated higher reactive oxidative species production than the wild type.This of finding provides potential links between occult HBV infection and liver disease progression. CONCLUSION: The presently obtained data indicate that deficiency in the secretion capacity of HBs Ag variants may have a pivotal function in the occult infections of HBV genotype C.