IFN- α and anti-inflammatory cytokines modulate the cellular uptake of HCV

Aims: IFN-α is the backbone of antiviral treatment for patients with chronic HCV infection. The mechanism of action for the antiviral effect of IFN-α, however, is still largely hypothetical. Therefore, the aim of this study was to analyze the influence of IFN- α and anti-inflammatory cytokines that may counteract the IFN-system (IL-10 and TGF- β) on the expression of molecules involved in HCV uptake (CD81, Claudin-1, SR-BI).

Material and methods: Huh-7 human hepatoma cells were treated with IFN-α, IL-10 or TGF-β and then incubated with MLV (mouse leukemia virus)-HCV pseudoparticles (HCVpp) expressing the viral envelope glycoproteins for 4h to achieve complete infection. Infectivity was measured by quantification of early reverse-transcribed long terminal repeats (LTR) of MLV by quantitative real-time PCR assay after 4h of contact with target cells. Huh-7 cells were treated with IFN-α, IL-10 or TGF- β and expression of CD81, Claudin-1 and SR-BI was analyzed by western blot, flow cytometry and quantitative realtime rt-PCR.

Results: Pretreatment of Huh-7 with IFN-α for 48h resulted in a significantly decreased HCV uptake while IL-10 and TGF- β pretreatment resulted in an increased HCV uptake. To elucidate the possible underlying molecular mechanisms, IFN-α induced modulation of the expression of CD 81, SR-BI and Claudin-1 was studied. CD81 and SR-BI expression on HuH-7 cells was not changed by IFN-α stimulation when analyzed by flow cytometry and western blot. In contrast, Claudin-1 expression was significantly downregulated by IFN-α. This could be shown for surface expression, total protein expression and mRNA expression. Treatment with TGF- β led to an increased expression of SR-BI.

Conclusions: These results show that IFN-α mediates its antiviral activity not solely by inhibition of HCV replication, but can also modulate the initial steps of infection by downregulation of Claudin-1 expression. On the contrary, the antiinflammatory cytokine TGF-β maybe enhances HCV uptake by up-regulating SR-BI expression therefore contributing to the propagationof HCV infection.