Constitutive but not inducible attenuation of transforming growth factor β signaling increases natural killer cell responses without directly affecting dendritic cells early after persistent viral infection.

Abstract

Rapid innate responses to viral encounters are crucial to shaping the outcome of infection, from viral clearance to persistence. Transforming growth factor β (TGF-β) is a potent immune suppressor that is upregulated early upon viral infection and maintained during chronic infections in both mice and humans. However, the role of TGF-β signaling in regulating individual cell types in vivo is still unclear. Using infections with two different persistent viruses, murine cytomegalovirus (MCMV) and lymphocytic choriomeningitis virus (LCMV; Cl13), in their natural rodent host, we observed that TGF-β signaling on dendritic cells (DCs) did not dampen DC maturation or cytokine production in the early stages of chronic infection with either virus in vivo. In contrast, TGF-β signaling prior to (but not during) chronic viral infection directly restricted the natural killer (NK) cell number and effector function. This restriction likely compromised both the early control of and host survival upon MCMV infection but not the long-term control of LCMV infection. These data highlight the context and timing of TGF-β signaling on different innate cells that contribute to the early host response, which ultimately influences the outcome of chronic viral infection in vivo. In vivo host responses to pathogens are complex processes involving the cooperation of many different immune cells migrating to specific tissues over time, but these events cannot be replicated in vitro. Viruses causing chronic infections are able to subvert this immune response and represent a human health burden. Here we used two well-characterized viruses that are able to persist in their natural mouse host to dissect the role of the suppressive molecule TGF-β in dampening host responses to infection in vivo. This report presents information that allows an increased understanding of long-studied TGF-β signaling by examining its direct effect on different immune cells that are activated very early after in vivo viral infection and may aid with the development of new antiviral therapeutic strategies.