Genetic Variation in the RSV fusion protein controls strain-dependent inflammasome activation and the development of a pathogenic Th17 response

Abstract

Abstract Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in young children worldwide. RSV-induced disease ranges from mild to severe, with severe disease correlating with increased levels of pro-inflammatory cytokines, including the Th17-associated cytokine, IL-17. To understand the viral factors that influence the induction of a pathogenic Th17 response, we compared the inflammatory responses elicited by different RSV strains. In contrast to the commonly used RSV A2 strain, RSV 2–20 infection resulted in increased protein levels of IL-6 and IL-1β, which were required to induce a pathogenic Th17 response. RSV 2–20 infection increased mucus production and airway hyperreactivity indicating strain-specific disease induction. RSV 2–20 and A2 induced similar expression of caspase-1, however, 2–20 infection resulted in increased levels of pro-IL-1β suggesting differential activation of inflammasome signal 1. Increased production of IL-1β following RSV 2–20 infection was dependent on TLR4 expression and signaling, a canonical inflammasome signal 1 activator. A recombinant A2 virus expressing the 2–20 fusion (F) protein induced IL-1β to similar levels as wild-type 2–20 indicating the 2–20 F protein is sufficient to increase pro-inflammatory cytokine production. Reversion of three-point mutations in a region likely to interact with host cells in the RSV A2/2–20 F recombinant virus to the A2 sequence significantly reduced IL-6 and IL-1β protein production. Our results demonstrate that genetic variation in the RSV F protein plays a crucial role in the induction of pro-inflammatory cytokines and modulating disease severity in the animal model and may contribute to differential RSV pathogenesis.