Identification of different degrees of hepatitis B virus (HBV) replication by serological (HBV-DNAp, HBcAg and HBV-DNA) and histological (HBcAg) methods

Characterization and risk of blood-borne virus transmission in organ transplantation: what are the priorities?

ABSTRACT 

Blood-borne virus transmission through organ transplantation, although rare, has been associated with severe complications in recipients. There are few data available to ascertain the risk of infection in organ transplantation for known and emerging pathogens, as most information comes from events of transmission, which are rare and not always well characterized. The balance between quality of life through organ transplantation and the risks of donor-derived infection can be improved through advances in donor screening, enhanced monitoring and a multidisciplinary approach to improving donor assessment and recipient biosurveillance. The involvement of investigators with clinical, laboratory, surveillance and policy expertise is critical to bridge research knowledge and clinical practice.

Persistent hepatitis B viral replication in a FVB/N mouse model: impact of host and viral factors

The mechanism underlying the chronicity of hepatitis B virus (HBV) infection has long been an interesting question. However, this mechanism remains unclear largely due to the lack of an animal model that can support persistent HBV replication and allow for the investigation of the relevant immune responses. In this study, we used hydrodynamic injection to introduce HBV replicon DNA into the livers of three different mouse strains: BALB/c, C57BL/6, and FVB/N. Interestingly, we found that an HBV clone persistently replicated in the livers of FVB/N mice for up to 50 weeks but was rapidly cleared from the livers of BALB/c and C57BL/6 mice. Flow cytometric analysis and quantitative reverse transcription PCR analysis of the mouse livers indicated that after DNA injection, FVB/N mice had few intrahepatic activated cytotoxic T lymphocytes (CTLs) and produced low levels of alanine aminotransferase, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and the CXCL9 and CXCL10 chemokines. These findings were in sharp contrast with those observed in BALB/c and C57BL/6 mice, reflecting a strong correlation between the degree of liver inflammation and viral clearance. Mutational analysis further demonstrated that a change of Asn-214 to Ser-214 in the HBV surface antigen rendered the persistent HBV clone clearable in FVB/N mice, which was accompanied by increased levels of activated CTL and upregulated expression of IFN-γ, CXCL9, and CXCL10 in the livers. These results indicate that the heterogeneity of the host factors and viral sequences may influence the immune responses against HBV. An inadequate activation of immune or inflammatory responses can lead to persistent HBV replication in vivo.

Immune effectors required for hepatitis B virus clearance

To better define the mechanism(s) likely responsible for viral clearance during hepatitis B virus (HBV) infection, viral clearance was studied in a panel of immunodeficient mouse strains that were hydrodynamically transfected with a plasmid containing a replication-competent copy of the HBV genome. Neither B cells nor perforin were required to clear the viral DNA transcriptional template from the liver. In contrast, the template persisted for at least 60 days at high levels in NOD/Scid mice and at lower levels in the absence of CD4(+) and CD8(+) T cells, NK cells, Fas, IFN-gamma (IFN-gamma), IFN-alpha/beta receptor (IFN-alpha/betaR1), and TNF receptor 1 (TNFR1), indicating that each of these effectors was required to eliminate the transcriptional template from the liver. Interestingly, viral replication was ultimately terminated in all lineages except the NOD/Scid mice, suggesting the existence of redundant pathways that inhibit HBV replication. Finally, induction of a CD8(+) T cell response in these animals depended on the presence of CD4(+) T cells. These results are consistent with a model in which CD4(+) T cells serve as master regulators of the adaptive immune response to HBV; CD8(+) T cells are the key cellular effectors mediating HBV clearance from the liver, apparently by a Fas-dependent, perforin-independent process in which NK cells, IFN-gamma, TNFR1, and IFN-alpha/betaR play supporting roles. These results provide insight into the complexity of the systems involved in HBV clearance, and they suggest unique directions for analysis of the mechanism(s) responsible for HBV persistence.

Expression of hepatitis B virus nuclear core antigen in young cirrhotic patients is associated with an unfavourable long-term outcome

The aim of this case control study was to investigate the clinical significance of hepatitis B virus nuclear core antigen (HBcAg) in young cirrhotic patients. Fifteen cirrhotic patients with nuclear HBcAg in the liver biopsies were included. Their clinicopathological parameters as well as the core gene sequences were compared with those of a sex- and age-matched (1 to 2) control group. The mean follow-up periods were 124 +/- 80 and 102 +/- 43 months, respectively. Expression of nuclear HBcAg in cirrhotic liver was significantly associated with higher aspartate aminotransferase levels (P = 0.001), alanine aminotransferase levels (P < 0.001), and alpha-fetoprotein levels (P = 0.002), as well as a shorter duration to develop hepatocellular carcinoma or liver decompensation (Kaplan-Meier method, P = 0.044). Sequence analysis revealed mutations on the nuclear localization signal (NLS) of core protein in five cirrhotic patients with nuclear HBcAg (Q171K in four and Q179K in one patients). Site-directed mutagenesis experiments demonstrated that both the Q171K and Q179K mutation enhanced nuclear localization of the core protein. In conclusion, expression of nuclear HBcAg in young cirrhotic patients was associated with more severe hepatitis activities as well as an unfavourable long-term outcome. Mutations on the NLS of core protein were selected in some patients with nuclear HBcAg.

Discordance of hepatitis B e antigen and hepatitis B viral deoxyribonucleic acid

Sera from 899 hepatitis B surface antigen (HBsAg) carriers from four separate ethnic groups (Caucasian, Australian Aboriginal, Melanesian, and Asian) were studied for their correlation for hepatitis B virus deoxyribonucleic acid (HBV DNA) and hepatitis B e antigen (HBeAg). Discordance, as signified by the absence of HBV DNA despite the presence of HBeAg, was unusual in Caucasians but frequently occurred in the other three ethnic groups (11-25%). Analysis by age showed that it occurred occasionally during childhood and, in this age group, may simply be part of the process of seroconversion with impending loss of HBeAg, whereas its greater prevalence in patients with liver disease may have a different mechanism. In sera obtained from Melanesians with hepatocellular carcinoma and Asians with chronic hepatitis, discordance was a common feature with HBV DNA being undetectable in those with HBeAg in 87% and 72%, respectively. A number of important implications flow from these observations pertinent to the use of HBeAg to detect replicating virus and the prognostic significance of HBeAg in HBsAg carriers when HBV DNA is undetectable.

Detection of HBeAg/anti-HBe immune complexes in the reactivation of hepatitis B virus replication among anti-HBe chronic carriers

Sixty-four chronic hepatitis B surface antigen (HBsAg) carriers with hepatitis B e antibody (anti-HBe) were followed in order to detect reactivations of hepatitis B virus (HBV) infection and to assess the incidence and specificity of hepatitis B e antigen/hepatitis B e antibody (HBeAg/anti-HBe) immune complexes (ICs). In 18 out of 19 patients who suffered an increase in alanine transaminase (ALT) values, serum HBV-DNA reappeared co-occurring with the peak(s) of transaminases. HBeAg/Anti-HBe immune complexes were detected in 17/18 (94.4%) patients positive for HBV-DNA. In nine of them, the appearance of immune complexes co-occurred with prednisone therapy, in two following seroconversion after recombinant interferon alpha-2A treatment, and spontaneously in the remaining seven patients. When ALT levels dropped to normal values, immune complexes as well as HBV-DNA became undetectable. In conclusion, the detection of HBeAg/anti-HBe immune complexes seems to be a specific method to detect HBV replication among anti-HBe positive patients.

Immunocytochemical and electron microscopic study of hepatitis B virus antigen and complete particle production in hepatitis B virus DNA transfected HepG2 cells

The relationship between the presence of hepatitis B virus antigens, their localization and hepatitis B virus replication was studied in different clones of cultured HepG2 hepatoblastoma cells transfected with cloned hepatitis B virus DNA. Intracellular hepatitis B virus antigens were detected by immunofluorescence. The production of these antigens was evaluated in the culture media by enzyme-linked immunoassay. Hepatitis B virus DNA was detected using dot-blot hybridization. Three types of HBcAg staining were observed in transfected HepG2 cells: (a) cells with nuclear HBcAg, (b) cells with cytoplasmic HBcAg and (c) cells with both nuclear and cytoplasmic HBcAg. Cell types b and c also expressed hepatitis B virus DNA in their culture media. Our results suggest that cytoplasmic HBcAg may be more involved than nuclear HBcAg in hepatitis B virus replication. The site of hepatitis B virus formation in hepatocytes was studied by electron microscopic examination of a specific hepatitis B virus producer clone, thereby allowing detection of intracellular Dane particles more easily than liver biopsy samples from infected patients. Dane particles and HBsAg filaments were found in large, dilated structures probably related to the endoplasmic reticulum. Budding of core particles into cisternae of endoplasmic reticulum-related structures appears to be a possible mechanism for hepatitis B virus formation; our results suggest that the exocytosis of cisternae to extracellular spaces may be a mechanism for release of hepatitis B virus particles.