Conjugated bilirubin reduces hepatitis E virus infectivity by modulating immunometabolic processes

Despite the landmark discovery of the hepatitis E virus (HEV) four decades ago and its status as the leading cause of viral hepatitis worldwide, the infection remains overlooked in numerous countries. Currently, there are no approved treatments for hepatitis E or licensed vaccines available for global distribution. The clinical presentation of infection is influenced by the host's immune response and may also be affected by metabolic factors. We previously reported an immunomodulatory role for conjugated bilirubin (cBR) in hepatitis A virus infection, and antiviral effects of this metabolite have been proposed. However, the impact of cBR on HEV infectivity and the mechanisms underlying this effect have yet to be elucidated. By combining (i) ex vivo analysis of HEV-infected patients, (ii) in vitro antigenic restimulation of peripheral blood mononuclear cells (PBMCs) cultured with different cBR doses, and (iii) in vitro infection of permissive cell lines, we found that cBR concentrations of 2 mg/dL lowered viral titers and increased IFN-γ release in patients with acute infection. Furthermore, antigenic restimulation of PBMCs cultured with 2 mg/dL cBR promoted positive interactions between TNF-α and metabolic signaling proteins such as Akt and ERK. Moreover, cBR induced the overproduction of IFN-γ by CD8+ T cells from individuals with prior HEV exposure and decreased viral titers in both acute and chronic infection models at concentrations greater than or equal to 0.3 mg/dL. These findings demonstrate that during HEV infection, cBR plays a significant role in modulating the interaction between immune and metabolic components, ultimately influencing viral infectivity.