| Alphaviruses are mosquito-borne viruses within the family Togaviridae . These positive-sense RNA viruses pose a significant human and equine public health threat due to their ability to cause explosive epidemics of infectious rheumatic disease and encephalitis. The AR86 strain of Sindbis virus (SINV, infectious clone: S300) is neurovirulent in adult mice. A critical viral genetic determinant of neurovirulence within S300 is a Threonine at nonstructural protein (nsP) 1 position 538, whereby introduction of an Isoleucine at this locus is attenuating in vivo. The mutant nsP1 T538I virus induces more type I interferon (IFN) and fails to efficiently block type I and II IFN signaling as compared to S300 virus. Importantly, nsP1 T538I replicates as well as S300 virus at early times postinfection within the central nervous system (CNS) of infected mice, however at late times post-infection, nsP1 T538I is more efficiently controlled and cleared. In this work, we investigated the components of the host innate and adaptive immune system that modulate AR86-induced neurologic disease.;Herein, we identify the IPS-1 pathway of intracellular RNA sensing as mediating protection from nsP1 T538I disease and driving viral clearance. Furthermore, we demonstrate that the TRIF-dependent pathway, which is essential for TLR3 and one pathway iv of TLR4 signaling, is moderately protective against the AR86 strain of SINV. IPS-1 and TRIF are adaptor molecules essential for signal transduction that results in the upregulation of interferon stimulated genes (ISGs), which in turn exert virus-specific antiviral activity. These studies reveal that two ISGs, IFIT1 and IFIT2, inhibit nsP1 T538I replication within IFN-β primed murine cells.;We further demonstrate protective roles for T and B cells during nsP1 T538I infection, while the viral control conferred by T and B cells did not require their intrinsic ability to respond to type I IFN. Finally, these studies demonstrate contradictory phenotypes during AR86 infection of IFN-gamma receptor and cytokine knockout mice, thereby challenging the paradigm of IFN-gamma-mediated noncytolytic clearance from neurons. In sum, these studies identify key innate immune sensing pathways that modulate alphavirus neurovirulence and also refine our understanding of the role of adaptive immunity during clearance of a neurovirulent alphavirus. |
