As the human tetraspanin CD81 binds hepatitis C virus (HCV) envelope glycoprotein E2, we addressed the role CD81 may play in cellular trafficking of HCV envelope proteins. Studies on HCV life cycle are complicated by the lack of a robust cell culture system; we therefore transfected mammalian cells with HCV E1‐E2 cDNA, with or without human CD81 (huCD81) cDNA. In the absence of huCD81, HCV envelope proteins are almost completely retained in the endoplasmic reticulum. Instead, when huCD81 is present, a fraction of HCV envelope proteins passes through the Golgi apparatus, matures acquiring complex sugars and is found extracellularly associated with exosomes. These are 60–100‐nm membrane vesicles enriched in tetraspanins, released into the extracellular milieu by many cell types and having fusogenic activity. We also report that human plasma contains exosomes and that in HCV patients, viral RNA is associated with these circulating vesicles. We propose that the HCV‐CD81 complex leaves cells in the form of exosomes, circulates in this form and exploits the fusogenic capabilities of these vesicles to infect cells even in the presence of neutralizing antibodies.

AIM: To investigate the usefulness of transient elastography by Fibroscan (FS), a rapid non-invasive technique to evaluate liver fibrosis, in the management of chronic hepatitis B virus (HBV) carriers. METHODS: In 297 consecutive HBV carriers, we studied the correlation between liver stiffness (LS), stage of liver disease and other factors potentially influencing FS measurements. In 87 chronic hepatitis B (CHB) patients, we monitored the FS variations according to the spontaneous or treatment-induced variations of biochemical activity during follow-up. RESULTS: FS values were 12.3 ± 3.3 kPa in acute hepatitis, 10.3 ± 8.8 kPa in chronic hepatitis, 4.3 ± 1.0 kPa in inactive carriers and 4.6 ± 1.2 kPa in blood donors. We identified the cut-offs of 7.5 and 11.8 kPa for the diagnosis of fibrosis ≥ S3 and cirrhosis respectively, showing 93.9% and 86.5% sensitivity, 88.5% and 96.3% specificity, 76.7% and 86.7% positive predictive value (PPV), 97.3% and 96.3% negative predictive value (NPV) and 90.1% and 94.2% diagnostic accuracy. At multivariate analysis in 171 untreated carriers, fibrosis stage (t = 13.187, P < 0.001), active vs inactive HBV infection (t = 6.437, P < 0.001), alanine aminotransferase (ALT) (t = 4.740, P < 0.001) and HBV-DNA levels (t = -2.046, P = 0.042) were independently associated with FS. Necroinflammation score (t = 2.158, > 10/18 vs≤ 10/18, P = 0.035) and ALT levels (t = 3.566, P = 0.001) were independently associated with LS in 83 untreated patients without cirrhosis and long-term biochemical remission (t = 4.662, P < 0.001) in 80 treated patients. During FS monitoring (mean follow-up 19.9 ± 7.1 mo) FS values paralleled those of ALT in patients with hepatitis exacerbation (with 1.2 to 4.4-fold increases in CHB patients) and showed a progressive decrease during antiviral therapy. CONCLUSION: FS is a non-invasive tool to monitor liver disease in chronic HBV carriers, provided that the pattern of biochemical activity is taken into account. In the inactive carrier, it identifies non-HBV-related causes of liver damage and transient reactivations. In CHB patients, it may warrant a more appropriate timing of control liver biopsies.