We previously reported that TJs impose a physical barrier and restrict viral access to receptors23 and that complex hepatocyte-like polarity limits HCV entry.18 To investigate whether binding of anti-CLDN1 antibodies to polarized human hepatoma cells perturbed TJ integrity, we assessed the ability of TJs to restrict the paracellular diffusion

of CMFDA from the BC lumen to the basolateral HDAC inhibitor mechanism medium (barrier function) as described.18 As shown in Fig. 2, the capacity of BC lumens to retain CMFDA was similar in polarized HepG2 cells treated with rat anti-CLDN1 antibodies, rat control serum, or PBS, whereas CMFDA retention was reduced in interferon-γ–treated HepG2 cells (Fig. 2B). These data suggest that anti-CLDN1 antibodies have no effect on TJ integrity. To investigate whether anti-CLDN1 antibodies could inhibit HCV infection, Huh7.5.1 cells were infected with chimeric J6/CF-JFH1 firefly luciferase reporter virus (Luc-Jc1)26, 29 in the presence of anti-CLDN1 or control antibodies. Fig. 3A shows that anti-CLDN1 serum inhibits Luc-Jc1 infection of Huh7.5.1 cells in a dose-dependent manner, whereas the control preimmune serum had no inhibitory effect. Neutralization of HCVcc infection correlated with binding of antibodies to the target cell line (Fig. 3B). To confirm that inhibition of Luc-Jc1

infection was mediated by anti-CLDN1 antibodies, we purified IgG from rat anti-CLDN1 and preimmune serum. As shown in Fig. 3C, anti-CLDN1 IgG but not control IgG markedly inhibited check details Luc-Jc1 HCVcc infection in a dose-dependent manner. These data demonstrate that the inhibitory effect of anti-CLDN1 serum was mediated by anti-CLDN1 IgG and not by other substances present in the serum. Infection experiments using primary human hepatocytes and HCVpp packaged with envelope glycoproteins 上海皓元医药股份有限公司 from genotypes 1-4 demonstrated that anti-CLDN1 blocking activity was similar for infection with HCV-bearing envelope

proteins of other genotypes (Fig. 3D). Taken together, these findings demonstrate that antibodies directed against the CLDN1 extracellular loops inhibit HCV infection in HCV permissive cell lines and human hepatocytes. We previously demonstrated that CD81 and SR-BI act in concert to mediate HCV entry.26 To investigate whether the three host factors CLDN1, CD81, and SR-BI act in a cooperative manner, we added low concentrations of anti-receptor antibodies simultaneously prior to HCV infection. The use of antibody concentrations that submaximally blocked HCV infection allowed us to observe additive or synergistic effects. First, we determined the ability of combinations of two out of the three antibodies to neutralize HCVcc infection. Fig. 4 shows an additive effect of the concomitant blocking of both CD81 and CLDN1 (Fig. 4B), SR-BI and CLDN1 (Fig. 4C), or CD81 and SR-BI (Fig. 4D). This effect was not observed when control IgG or control serum was used in combination with anti-CLDN1 antibodies (data not shown).