title: Role of hepatitis B virus genotype D & its mutants in occult hepatitis B infection.
abstract: OBJECTIVE
  Non-detection of hepatitis B virus (HBV) envelope protein (hepatitis B surface antigen, HBsAg) in a chronically HBV infected individual has been described as occult infection. One possible reason for this phenotype is alteration in large (L-HBsAg) to small (S-HBsAg) envelope protein ratio associated with reduced or non secretion of HBsAg. This results in quantitative levels of serum HBsAg below the detection limit of enzyme immunoassays. Genotype D of HBV has a characteristic 33 nucleotide (nt) deletion upstream of the pre-S2/S promoter. This deletion may reduce HBsAg secretion in occult infection patients infected with genotype D HBV. Additional deletions in the pre-S2/S promoter may further aggravate reduced HBsAg secretion in patients infected with genotype D HBV. Thus, the aim of the present study was to determine the role of genotype D specific 33nt deletion and additional pre-S2/S promoter deletions in causing reduced or no secretion of HBsAg, in occult infection. Since these deletions overlap virus polymerase, their effect on virus replication was also investigated.
  
  
  METHODS
  We examined the in vitro expression of HBsAg, ratio of cure and 'e' antigen (HBcAg/HBeAg), their secretion and virus replication, using overlength 1.3 mer/1.86 mer genotype A replicons, and genotype D replicons with and without additional pre-S2/S promoter deletions from cases of occult infection.
  
  
  RESULTS
  Genotype D replicon showed a decrease in HBsAg secretion compared to the wild-type genotype A. Genotype D replicons carrying additional pre-S2/S promoter deletions, showed further reduction in HBsAg secretion, demonstrated presence of intracellular HBcAg/HBeAg, virus replication intermediates and 'e' antigen secretion.
  
  
  CONCLUSIONS
  The characteristic 33 nt deletion of genotype D HBV reduces HBsAg secretion. Additional pre-S2/S promoter deletions may further diminish HBsAg secretion, leading to occult infection. Pre-S2/S promoter deletions do not affect HBV replication.
authors.affiliation: Department of Pathology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Sonali
authors.initials: S
authors.lastname: Sengupta
authors.forename: Subrat Kumar
authors.initials: SK
authors.lastname: Panda
authors.forename: Subrat Kumar
authors.initials: SK
authors.lastname: Acharya
authors.forename: Hemlata
authors.initials: H
authors.lastname: Durgapal
mesh_terms: D004797:Enzyme-Linked Immunosorbent Assay; D005838:Genotype; D006509:Hepatitis B / Q000821:virology*; D006514:Hepatitis B Surface Antigens / Q000097:blood; D006515:Hepatitis B virus / Q000235:genetics* / Q000276:immunology; D006801:Humans; D009154:Mutation
chemical_list: D006514:Hepatitis B Surface Antigens