Hepatitis B virus particles activate toll‐like receptor 2 signaling initial upon infection of primary human hepatocytes

To date conflicting data exist, whether hepatitis B virus (HBV) has the ability to induce innate immune responses. Here, we investigated cellular changes after the first-contact between HBV and primary human hepatocytes (PHH) in vitro and in vivo. The exposure of PHH to HBV particles resulted in nuclear translocation of NFkappaB, followed by the expression and secretion of inflammatory cytokines (IL1B, IL6 and TNF). UV irradiation of viral particles suppressed HBV infectivity but not the induction of cytokines in PHH, suggesting that the inoculum contains the immune inducing agent. Purified HBV particles on the whole, that were prepared from HBV DNA-positive and protein rich fractions after heparin column separation, still had immune-inducing capacity in PHH. The HBV-induced gene expression profile was similar to that induced by TLR2 ligand Pam3Cys, but different from those induced by the viral sensors TLR3 or TLR7-9. Treatment of PHH with both, HBV particles and Pam3Cys led to phosphorylation of ERK1, JNK and p38 mitogen-activated protein kinases as well as NFkappaB. Finally, HBV-induced gene expression could be neutralized by TLR2-specific antibodies. Of note, pre-treatment with an HBV entry inhibitor attenuated the TLR2-mediated response to HBV, suggesting a receptor binding-related mechanism. In liver-humanized uPA/SCID/beige mice challenged with HBV in vivo immune induction could only marginally be seen. Conclusions: Primary human hepatocytes are able to sense HBV particles via TLR2 leading to an activation of anti-HBV immune responses in vitro. These findings challenge the previously described stealth properties of HBV.