title: Functional analysis of 'a' determinant mutations associated with occult HBV in HIV-positive South Africans.
abstract: Occult hepatitis B is defined by the presence of hepatitis B virus (HBV) DNA in the absence of hepatitis B surface antigen (HBsAg). Occult HBV is associated with the development of hepatocellular carcinoma, reactivation during immune suppression, and virus transmission. Viral mutations contribute significantly to the occult HBV phenotype. Mutations in the 'a' determinant of HBsAg are of particular interest, as these mutations are associated with immune escape, vaccine escape and diagnostic failure. We examined the effects of selected occult HBV-associated mutations identified in a population of HIV-positive South Africans on HBsAg production in vitro. Mutations were inserted into two different chronic HBV backbones and transfected into a hepatocyte-derived cell line. HBsAg levels were quantified by enzyme-linked immunosorbent assay (ELISA), while the detectability of mutant HBsAg was determined using an HA-tagged HBsAg expression system. Of the seven mutations analysed, four (S132P, C138Y, N146D and C147Y) resulted in decreased HBsAg expression in one viral background but not in the second viral background. One mutation (N146D) led to a decrease in HBsAg detected as compared to HA-tag, indicating that this mutation compromises the ability of the ELISA to detect HBsAg. The contribution of occult-associated mutations to the HBsAg-negative phenotype of occult HBV cannot be determined adequately by testing the effect of the mutation in a single viral background, and rigorous analysis of these mutations is required.
authors.affiliation: University of Cincinnati College of Medicine.
authors.forename: Eleanor A
authors.initials: EA
authors.lastname: Powell
authors.affiliation: University of Cincinnati College of Medicine.
authors.forename: Ceejay L
authors.initials: CL
authors.lastname: Boyce
authors.affiliation: Sefako Makgatho Health Sciences University.
authors.forename: Maemu P
authors.initials: MP
authors.lastname: Gededzha
authors.affiliation: Sefako Makgatho Health Sciences University.
authors.forename: Selokela G
authors.initials: SG
authors.lastname: Selabe
authors.affiliation: Sefako Makgatho Health Sciences University; South Africa Medical Research Council.
authors.forename: M Jeffrey
authors.initials: MJ
authors.lastname: Mphahlele
authors.affiliation: Division of Digestive Diseases ML 0595 231 Albert Sabin Way, University of Cincinnati, University of Cincinnati College of Medicine, USA.
authors.forename: Jason T
authors.initials: JT
authors.lastname: Blackard
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000821:virology; D045744:Cell Line, Tumor; D004279:DNA, Viral / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D006679:HIV Seropositivity / Q000150:complications; D006514:Hepatitis B Surface Antigens / Q000097:blood* / Q000235:genetics*; D006515:Hepatitis B virus / Q000235:genetics*; D019694:Hepatitis B, Chronic / Q000175:diagnosis* / Q000821:virology; D006801:Humans; D008113:Liver Neoplasms / Q000821:virology; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D013019:South Africa
chemical_list: D004279:DNA, Viral; D006514:Hepatitis B Surface Antigens