To investigate the molecular and clinical features of human pegivirus-associated encephalitis

Human pegivirus-1 (HPgV-1) is a positive sense, single-stranded RNA virus that is a member of the Flaviviridae family. We recently reported HPgV-1 infection in the brains of two patients with fatal leukoencephalitis (Balcom, Doan et al., 2018).

In vitro and in vivo studies of HPgV-1 infection were performed in cultured human astrocytes and in autopsied brain using RT-PCR and immunodetection methods.

We transfected astrocytoma U251 cells with a molecular clone of HPgV-1 from which viral stocks were prepared. Primary human astrocyte cultures were then infected using these stocks and immunodetection of NS5A was performed 4, 7 and 14 days post-infection (PI). The mean viral spread (HPgV-1+ immunodetection/μm³) peaked at Day 7 PI and droplet digital PCR (ddPCR) analyses of astrocyte culture supernatants showed 7577, 10834 and 2905 viral RNA copies/mL at Days 4, 7 and 14 PI, respectively. Viral antigen detection in astrocytes was associated with cell lysis and cell death, evidenced by increased lactose dehydrogenase in the media and a decrease in DAPI intensity. To determine the in vivo neuroinflammatory effects of HPgV-1 infection, we identified an additional 11 (of 109) patients with HPgV-1 brain infection (700-11,000 HPgV-1 RNA copies/gm). The expression of proinflammatory cytokine genes (IL1B, TNFA, IL6) was markedly increased in the brains from patients with HPgV-1 co-infected with HIV-1 (n=6) compared to HPgV-1 mono-infected (n=5) patients.

These studies indicate that HPgV-1 is a neurotropic virus with the capacity to infect and spread in primary human glial cells. HPgV-1 might act synergistically with HIV-1 to promote neuroinflammation in vivo. These findings highlight the importance of considering HPgV-1 as a potential cause of encephalitis in humans and exploring its associated neuroinflammation implicated in other neurological diseases.