Regulation of immunopathology in hepatitis B virus infection

Viral Hepatitides, Inflammation and Tumour Microenvironment

In this chapter, we discuss the role of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in the establishment of hepatocellular carcinoma (HCC), highlighting the key role of the multiple, non-mutually exclusive, pathways involved in the modulation of immune responses and in the orchestration of a chronic low-level inflammation state favouring HCC development. In particular, we discuss (i) HCC as a classical paradigm of inflammation-linked cancer; (ii) the role of the most relevant inflammatory cytokines involved (i.e. IL-6, TNF-α, IL-18, IL-1β, TGF-β IL-10); (iii) the role of T cell exhaustion by immune checkpoints; (iv) the role of the Wnt3a/β-catenin signalling pathway and (v) the role of different subsets of suppressor cells.

Attenuated viral hepatitis in Trem1-/- mice is associated with reduced inflammatory activity of neutrophils

TREM1 (Triggering Receptor Expressed on Myeloid Cells 1) is a pro-inflammatory receptor expressed by phagocytes, which can also be released as a soluble molecule (sTREM1). The roles of TREM1 and sTREM1 in liver infection and inflammation are not clear. Here we show that patients with hepatitis B virus (HBV) or hepatitis C virus (HCV) infection manifest elevated serum levels of sTREM1. In mice, experimental viral hepatitis induced by infection with Lymphocytic Choriomeningitis Virus (LCMV)-WE was likewise associated with increased sTREM1 in serum and urine, and with increased TREM1 and its associated adapter molecule DAP12 in the liver. Trem1−/− mice showed accelerated clearance of LCMV-WE and manifested attenuated liver inflammation and injury. TREM1 expression in the liver of wild-type mice was mostly confined to infiltrating neutrophils, which responded to LCMV by secretion of CCL2 and TNF-α, and release of sTREM1. Accordingly, the production of CCL2 and TNF-α was decreased in the livers of LCMV-infected Trem1−/− mice, as compared to LCMV-infected wildtype mice. These findings indicate that TREM1 plays a role in viral hepatitis, in which it seems to aggravate the immunopathology associated with viral clearance, mainly by increasing the inflammatory activity of neutrophils.