Hepatitis B Virus Particles Activate Toll‐Like Receptor 2 Signaling Initially Upon Infection of Primary Human Hepatocytes

Abstract

BaCKgRoUND aND aIMS: To date, conflicting data exist as to 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. appRoaCH aND ReSUltS: The exposure of PHH to HBV particles resulted in nuclear translocation of NFκB, followed by the expression and secretion of inflammatory cytokines (IL [interleukin] 1B, IL6, and TNF [tumor necrosis factor]). Ultraviolet 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, which 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 toll-like receptor 2 (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 ERK (extracellular signal-regulated kinase), JNK, and p38 mitogen-activated protein kinases as well as NFκB (nuclear factor kappa B). Finally, HBV-induced gene expression could be neutralized by TLR2-specific antibodies. Of note, pretreatment with an HBV entry inhibitor attenuated the TLR2-mediated response to HBV, suggesting a receptor binding-related mechanism. In liver-humanized uPA/severe combined immunodeficient (SCID)/beige mice challenged with HBV in vivo, immune induction could only marginally be seen. CoNClUSIoNS: PHHs are able to sense HBV particles through TLR2, leading to an activation of anti-HBV immune responses in vitro. These findings challenge the previously described stealth properties of HBV. (Hepatology 2020;0:1-16). C hronic hepatitis caused by hepatitis B virus (HBV) infection is among the most frequent causes for liver-related morbidity and mortality. Persistent infections mostly occur in perinatal and childhood infections as well as in immunocompromised

Pattern Recognition Receptors: Significance of Expression in the Liver

“…The HBVinduced gene expression profile was comparable to that of a TLR2 ligand (Pam3Cys) but distinct from those known as viral sensors, TLR3 or TLR7/9. These findings contrast with the abovementioned stealth properties of HBV (Zhang et al 2020). On the other hand, Guo et al (2009) studied the effect of the PRRs adaptors (TRIF, RIG-1/MDA5, IPS-1) on HBV + co-transfected cells (HepG2 and Huh7).…”

Hepatitis B Virus DNA is a Substrate for the cGAS/STING Pathway but is not Sensed in Infected Hepatocytes

“…Its interplay with the signaling pathways leading to IFN production is still a matter of debate. Some publications have described a type I and III IFN or pro-inflammatory response to HBV infection in cultured hepatocytes [3][4][5][6][7]. HBV may also induce pro-inflammatory cytokines in immune cells such as Kupffer cells, the liver macrophages, even if they are not productively infected [8][9][10].…”

“…During the preparation of this manuscript, a report was published suggesting that HBV stimulates the TLR-2 pathway leading to NF-κB activation and production of pro-inflammatory cytokines [7]. The authors suggested that a receptor-binding mechanism might be involved in this response.…”

Hepatitis B virus particles activate B cells through the TLR2–MyD88–mTOR axis

“…However, lipoprotein contamination of the TLR2/4 pathway originating from the bacterial purification system could not be excluded 4,5 . Our recent studies indicated TLR2 as a contributor to T cell-dependent hydrodynamic HBV infection clearance in mice and primary human hepatocyte recognition of nascent HBV particles by TLR2 towards the activation of anti-HBV immune responses in vitro which challenges the former classification of HBV as "stealth" virus 6,7 . Moreover, impacting of TLR activation on the glycolytic metabolism drives macrophage and T-cell activation, suggesting TLR regulation of mTOR-integrated immune and metabolic processes [8][9][10][11][12][13] .…”

“…Our previous studies showed that exposure of hepatic cells including hepatocytes, liver sinusoidal cells, and Kupffer cells to HBVs or the canonical TLR2 ligand P3C resulted in diverse cellular responses 6,[23][24][25][26] . Thus, now we asked whether and how exposure of B cells to HBVs changes their activation status.…”