Inflammatory response triggered by avian hepatitis E virus in vivo and in vitro

Hepatitis E virus (HEV) is relevant to public health worldwide, and it affects a variety of animals. Big liver and spleen disease (BLS) and hepatitis-splenomegaly syndrome (HSS) associated with avian HEV (aHEV) were first reported in 1988 and in 1991, respectively. Here, cell culture-adapted aHEV genotype 3 strain, YT-aHEV (YT strain), a typical genotype isolated in China, was used for basic and applied research. We evaluated liver injury during the early stages of infection caused by the YT strain in vivo. Both in vivo and in vitro experimental data demonstrated that viral infection induces innate immunity, with mRNA expression levels of two key inflammatory factors, interleukin-1 beta (IL-1 beta) and IL-18, significantly upregulated. The YT strain infection was associated with the activation of Toll-like receptors (TLRs), nuclear factor kappa B (NF-kappa B), caspase-1, and NOD-like receptors (NLRs) in the liver and primary hepatocellular carcinoma epithelial cells (LMH). Moreover, inhibiting c-Jun N-terminal kinase, extracellular signal-regulated kinase (ERK1 or 2), P38, NF-kappa B, or caspase-1 activity has different effects on NLRs, and there is a mutual regulatory relationship between these signaling pathways. The results show that SB 203580, U0126, and VX-765 inhibited IL-1 beta and IL-18 induced by the YT strain, whereas Pyrrolidinedithiocarbamate (PDTC) had no significant effect on the activity of IL-1 beta and IL-18. Pretreatment of cells with SP600125 had an inhibitory effect on IL-18 but not on IL-1 beta. The analysis of inhibition results suggests that there is a connection between Mitogen-activated protein kinase (MAPK), NF-kappa B, and the NLRs signaling pathways. This study explains the relationship between signaling pathway activation (TLRs, NF-kappa B, MAPK, and NLR-caspase-1) and viral-associated inflammation caused by YT strain infection, which will help to dynamic interaction between aHEV and host innate immunity.