Traces of hepatitis B virus (HBV) genome can persist for years following recovery from hepatitis B. To determine overall duration, molecular characteristics, and pathological implications of this serologically undetectable form of hepadnaviral carriage, we have analyzed the expression of transcriptionally active virus genomes, their infectivity, and examined liver alterations during the natural lifespan of woodchucks convalescent from acute infection with HBVrelated woodchuck hepatitis virus (WHV). In this study, we document lifelong persistence of scanty amounts of replicating virus both in the liver and lymphatic system after spontaneous resolution of an episode of experimental hepadnaviral hepatitis. Antibodies to virus nucleocapsid (core) were found to be the most reliable immunovirological marker coexisting with occult infection. In the majority of convalescent woodchucks, serial liver biopsies showed protracted minimal to mild necroinflammation with periods of normal morphology; however, hepatocellular carcinoma (HCC) ultimately developed in 2 of 9 animals studied. Inocula derived from lymphoid cells of convalescent animals induced classical acute hepatitis in virus-naive woodchucks that progressed to chronic hepatitis and HCC in 1 of the animals, demonstrating infectivity and pathogenic competence of the carried virus. Our results reveal that low levels of infectious WHV and residual hepatic inflammation usually continue for life after resolution of hepatitis and that this recovery does not avert HCC development. They also demonstrate that, in addition to the liver, the lymphatic system is the site of the occult lifelong maintenance of replicating hepadnavirus. (HEPATOLOGY 1999;29:928-938.)Current evidence indicates that carriage of minute quantities of hepatitis B virus (HBV) genome can continue for years following complete clinical and serological recovery from acute hepatitis B. 1-5 In these convalescent patients, HBV DNA have been detected both in serum and in circulating lymphomononuclear cells, often despite the presence of neutralizing antibodies to virus envelope (hepatitis B surface antigen) 2,3,5 and a vigorous polyclonal HBV-specific cytotoxic T-cell response. 3,4,6 In addition, traces of hepatitis B surface antigen and HBV-DNA-reactive particles with physicochemical properties of intact virions have been detected in the circulation of some of the recovered individuals. 2 These findings imply that HBV eradication does not coincide with the rise of antivirusspecific humoral and cellular immune responses and with clinical resolution of acute hepatitis.It is expected that this serologically undetectable persistence of HBV may have important epidemiological and pathogenic implications, whose range has yet to be established. This assumption is based on a growing number of observations indicating that HBV infection can appear in recipients of organs from HBV serologically negative donors, [7][8][9][10][11][12] and that hepatocellular carcinoma (HCC) with integrated HBV genomic sequences can arise in ...

The importance of effective immune responses in recovery from acute hepadnaviral hepatitis has been demonstrated. However, there is no conclusive delineation of virological and immunological events occurring in the liver immediately after hepadnavirus invasion and during the preacute phase of infection. These very early events might be of primary importance in determining the recovery or progression to chronic hepatitis and the intrinsic hepadnaviral propensity to persist. In this study, applying the woodchuck model of acute hepatitis B, the hepatic kinetics of hepadnavirus replication and activation of genes encoding cytokines, cytotoxicity effectors, and immune cell markers were quantified in sequential liver biopsies collected from 1 h postinoculation onward by sensitive real-time cDNA amplification assays. The results revealed that hepadnavirus replication is established in the liver as early as 1 hour after infection. In 3 to 6 h, significantly augmented intrahepatic transcription of gamma interferon and interleukin-12 were evident, suggesting activation of antigen-presenting cells. In 48 to 72 h, NK and NKT cells were activated and virus replication was transiently but significantly reduced, implying that this early innate response is at least partially successful in limiting virus propagation. Nonetheless, T cells were activated 4 to 5 weeks later when hepatitis became histologically evident. Collectively, our data demonstrate that virus replication is initiated and the innate response activated in the liver soon after exposure to a liver-pathogenic dose of hepadnavirus. Nevertheless, this response is unable to prompt a timely adaptive T-cell response, in contrast to infections caused by other viral pathogens.

Hepadnavirus at very low doses establishes in woodchucks asymptomatic, serologically undetectable but molecularly evident persistent infection. This primary occult infection (POI) preferentially engages the immune system and initiates virus-specific T cell response in the absence of antiviral antibody induction. The current study aimed to determine whether POI with time may culminate in serologically identifiable infection and hepatitis, and what are, if any, its pathological consequences. Juvenile woodchucks were intravenously injected with inocula containing 10 or 100 virions of woodchuck hepatitis virus (WHV) to induce POI and followed for life or up to 5.5 years thereafter. All 10 animals established molecularly detectable infection with virus DNA in serum (<100–200 copies/mL) and in circulating lymphoid cells, but serum WHV surface antigen and antibodies to WHV core antigen remained undetectable for life. By approximately 2.5–3.5 years post-infection, circulating virus transiently increased to 103 copies/mL and virus replication became detectable in the livers, but serological markers of infection and biochemical or histological evidence of hepatitis remained undetectable. Nonetheless, typical hepatocellular carcinoma (HCC) developed in 2/10 animals. WHV DNA integration into hepatic and lymphatic system genomes was identified in 9/10 animals. Virus recovered from the liver virus-negative or virus-positive phases of POI displayed the wild-type sequence and transmitted infection to healthy woodchucks causing hepatitis and HCC. In summary, for the first time, our data demonstrate that an asymptomatic hepadnaviral persistence initiated by very small amounts of otherwise pathogenic virus, advancing in the absence of traditional serological markers of infection and hepatitis, coincides with virus DNA integration into the host's hepatic and immune system genomes, retains liver pro-oncogenic potency and is capable of transmitting liver pathogenic infection. This emphasizes the role for primary occult hepatitis B virus infection in the development of seemingly cyptogenic HCC in seronegative but virus DNA reactive patients.

Antibodies against virus nucleocapsid (anticore) normally accompany hepadnaviral hepatitis but they may also occur in the absence of symptoms and other serological indicators of the infection. This situation can be encountered following a clinically and serologically unapparent exposure to hepatitis B virus (HBV) or after recovery from hepatitis B. In this study, woodchucks inoculated with woodchuck hepatitis virus (WHV) were investigated to determine the relationship between anticore detection and the molecular status of virus replication in a primary WHV surface antigen (WHsAg)-negative infection or long-after resolution of WHV hepatitis. Serial, parallel samples of sera, peripheral blood mononuclear cells (PBMC) and liver tissue, collected for more than 5 years after inoculation with virus, were examined for WHV DNA by highly sensitive polymerase chain reaction (PCR)/nucleic acid hybridization assays. Sera were also tested for WHV DNA after DNase treatment and for WHV DNA and WHsAg after concentration in sucrose. Liver and PBMC were examined for WHV covalently closed circular DNA and viral RNA transcripts by PCR-based techniques to assess virus replication status. The study showed that anticore antibodies existing in the absence of other serological markers are a reliable indicator of occult WHV infection. This state can be accompanied by traces of circulating particles behaving as intact virions and by intermittent minimal-to-mild liver inflammation. In conclusion, the long-term presence of anticore antibodies alone is a consequence of sustained restimulation of the immune system by virus nucleocapsid produced during low-level hepadnaviral assembly. ( A ntibodies to hepatits B virus (HBV) core antigen (anti-HBc) coexist with HBV surface antigen (HBsAg) in symptomatic infection and can persist along with antibodies to HBsAg (anti-HBs) or without them for life after recovery from hepatitis B. 1,2 They may also occur in the pre-acute phase of hepatitis prior to the appearance of HBsAg. 3 Absence of anti-HBc is rare in HBV infection and has been attributed to aberrant immunological response to the virus or to infection with viral variants. The detection of anti-HBc as the only serological marker of HBV exposure ("isolated anti-core" or "anti-core alone") has been found in up to 10%-20% of blood donors in endemic areas. 4,5 Since anti-HBc-like reactivity was occasionally seen after HBV vaccination, this result has raised doubts as to the reliability of antiHBc testing. 6,7 However, individuals with isolated antiHBc showed the highest rates of HBV DNA detection by specific polymerase chain reaction (PCR) assays, 5,8 -11 suggesting ongoing low-level HBV infection despite the absence of classical serological markers. This outcome was consistent with the earlier findings of anti-HBc along with HBV DNA in serum and peripheral blood mononuclear cells (PBMC) 12 and a vigorous cytotoxic T-lymphocyte response to HBV antigens in apparently completely healthy individuals years after recovery from