title: The hepatitis B e antigen (HBeAg) targets and suppresses activation of the toll-like receptor signaling pathway.
abstract: OBJECTIVE
  Viruses target innate immune pathways to evade host antiviral responses. Recent studies demonstrate a relationship between hepatitis B disease states and the host's innate immune response, although the mechanism of immunomodulation is unknown. In humans, the innate immune system recognizes pathogens via pattern recognition receptors such as the Toll-like receptors (TLR), initiating anti-inflammatory responses. TLR expression and pro-inflammatory cytokine production is reduced in hepatitis B e antigen (HBeAg)-positive patients following TLR stimulation. The aim of this study was to investigate interactions between TLR signaling pathways and the mature HBeAg protein localized in the cytosol.
  
  
  METHODS
  The ability of HBeAg to inhibit TLR signaling and association with TLR adapters was evaluated by immunoprecipitation, immunostaining, and reporter studies.
  
  
  RESULTS
  Our findings show that HBeAg co-localizes with Toll/IL-1 receptor (TIR)-containing proteins TRAM, Mal, and TLR2 at the sub-cellular level, which was not observed for Hepatitis B core antigen. Co-immunoprecipitation analysis demonstrated HBeAg interacted with TIR proteins Mal and TRAM, while a mutated HBeAg ablated interaction between Mal and MyD88. Importantly, HBeAg also disrupted homotypic TIR:TIR interaction critical for TLR-mediated signaling. Finally, HBeAg suppressed TIR-mediated activation of the inflammatory transcription factors, NF-κB and Interferon-β promoter activity.
  
  
  CONCLUSIONS
  Our study provides the first molecular mechanism describing HBeAg immunomodulation of innate immune signal transduction pathways via interaction and targeting of TLR-mediated signaling pathways. These finding suggest the mechanism as to how HBeAg evades innate immune responses contributing to the pathogenesis of chronic hepatitis B infection and the establishment of viral persistence.
authors.affiliation: Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia.
authors.forename: Tali
authors.initials: T
authors.lastname: Lang
authors.forename: Camden
authors.initials: C
authors.lastname: Lo
authors.forename: Narelle
authors.initials: N
authors.lastname: Skinner
authors.forename: Stephen
authors.initials: S
authors.lastname: Locarnini
authors.forename: Kumar
authors.initials: K
authors.lastname: Visvanathan
authors.forename: Ashley
authors.initials: A
authors.lastname: Mansell
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000595:Amino Acid Sequence; D006528:Carcinoma, Hepatocellular; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D057809:HEK293 Cells; D006513:Hepatitis B e Antigens / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D019698:Hepatitis C, Chronic / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D056747:Immunomodulation / Q000276:immunology; D016899:Interferon-beta / Q000378:metabolism; D008113:Liver Neoplasms; D026901:Membrane Transport Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009185:Myelin Proteins / Q000378:metabolism; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D051193:Toll-Like Receptors / Q000276:immunology / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D006513:Hepatitis B e Antigens; C569026:MAL protein, human; C507779:MYD88 protein, human; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D011510:Proteolipids; C480228:TICAM2 protein, human; D051193:Toll-Like Receptors; D016899:Interferon-beta