During persistent viral infections, chronic immune activation, negative immune regulator expression, an elevated interferon signature and lymphoid tissue destruction correlate with disease progression. Here, we demonstrate that blockade of type 1 interferon (IFN-I) signaling using a type 1 interferon receptor neutralizing antibody reduced immune system activation, decreased expression of negative immune regulatory molecules and restored lymphoid architecture in mice persistently infected with lymphocytic choriomeningitis virus (LCMV). IFN-I blockade both prior to and following establishment of persistent virus infection resulted in enhanced virus clearance and was CD4 T-cell-dependent. Hence, we demonstrate a direct causal link between IFN-I signaling, immune activation, negative immune regulator expression, lymphoid tissue disorganization and virus persistence. Our results suggest therapies that target IFN-I may help control persistent virus infections.

Summary Although type I interferon (IFN-I) is thought to be beneficial against microbial infections, persistent viral infections are characterized by high interferon signatures suggesting that IFN-I signaling may promote disease pathogenesis. During persistent lymphocytic choriomeningitis virus (LCMV) infection, IFNα and IFNβ are highly induced early after infection and blocking IFN-I receptor (IFNAR) signaling promotes virus clearance. We assessed the specific roles of IFNβ versus IFNα in controlling LCMV infection. While blockade of IFNβ alone does not alter early viral dissemination, it is important in determining lymphoid structure, lymphocyte migration, and anti-viral T cell responses that lead to accelerated virus clearance, approximating what occurs during attenuation of IFNAR signaling. Comparatively, blockade of IFNα was not associated with improved viral control but with early dissemination of virus. Thus, despite their use of the same receptor, IFNβ and IFNα have unique and distinguishable biologic functions, with IFNβ being mainly responsible for promoting viral persistence.

Therapeutic vaccination is a potentially powerful strategy to establish immune control and eradicate persistent viral infections. Large and multifunctional antiviral T cell responses are associated with control of viral persistence; however, for reasons that were mostly unclear, current therapeutic vaccination approaches to restore T cell immunity and control viral infection have been ineffective. Herein, we confi rmed that neutralization of the immunosuppressive factor interleukin (IL)-10 stimulated T cell responses and improved control of established persistent lymphocytic choriomeningitis virus (LCMV) infection. Importantly, blockade of IL-10 also allowed an otherwise ineffective therapeutic DNA vaccine to further stimulate antiviral immunity, thereby increasing T cell responses and enhancing clearance of persistent LCMV replication. We therefore propose that a reason that current therapeutic vaccination strategies fail to resurrect/sustain T cell responses is because they do not alleviate the immunosuppressive environment. Consequently, blocking key suppressive factors could render ineffective vaccines more effi cient at improving T cell immunity, and thereby allow immune-mediated control of persistent viral infection.

Arenaviruses are a major cause of hemorrhagic fevers endemic to Sub-Saharan Africa and South America, and thus a major public health and medical concern. The prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is widely used as a model system for studying persistent and acute infections, as well as for gaining an understanding of mammalian immune function. When originally characterized three decades ago, the LCMV isolate, Armstrong, which causes an acute infection in adult mice, was found to differ from the LCMV Clone 13 strain that causes a persistent infection by two amino acid changes, one within the virus surface glycoprotein (GP1: F260L) and the other within the virus L polymerase (K1076Q). Mutation F260L was considered solely responsible for the exceptionally strong binding affinity of Clone 13 (L at GP1 260) to its cellular receptor, α-dystroglycan, which among cells of the immune system is preferentially expressed on dendritic cells, and consequently, alters dendritic cell function leading to viral persistence. Recently, we noted a previously overlooked nucleotide difference between these two strains that results in an additional amino acid change in GP1, N176D. To investigate the potential contribution of this newly identified mutation to the Clone 13 phenotype, we used reverse-genetics approaches to generate recombinant LCM viruses with each of these individual mutations. Phenotypic characterization of these rLCMV showed that mutation F260L, but not N176D, in the GP1 of LCMV is essential for mediating the long-term persistence of Clone 13 infections. This work emphasizes the importance of subtle differences in viral strains that determine disease outcomes.

Viral hemorrhagic fevers caused by the arenaviruses Lassa virus in Africa and