The Pathogen Recognition Receptor RIG-I is Functional in Platelets and Limits Thrombotic Responses

Influenza is associated with increased thrombotic risk, and its viral RNA (vRNA) can be sensed by pattern-recognition receptor RIG-I, but the function of RIG-I in platelets remains unknown. We sought to determine whether RIG-I can signal in platelets and contribute to thrombotic outcomes. Using RT-qPCR, SDS-PAGE, NATIVE-PAGE, and proteomic methods in platelets from non-infected and influenza-infected patients, we show that RIG-I is present and functional. Platelet-RIG-I activation by influenza-derived-vRNA did not result in uniform α- or δ-granule release, or to interferon-pathway activation. Instead, RIG-I signaled through MAVS to increase MLKL-phosphorylation (pMLKL), oligomerization, and S100A10 (but not S100A8/A9) release and surface presence. Oligomerized pMLKL led to surface punctures, evident by scanning electron microscopy, which were visible in both platelets and thrombin-induced platelet clots. Consistent with S100A10 surface localization, RIG-I activation in presence of plasminogen reduced platelet aggregation and led to increased disaggregation in presence of urokinase-type plasminogen activator. Disruption of RIG-I/MAVS signaling through MAVS deficiency was associated with increased thrombotic burden and shorter FeCl₃-induced carotid artery occlusion times during influenza infection in vivo. Consistent changes in occlusion burden were observed in the pulmonary veins of infected mice, where occluded area inversely correlated with leukocyte presence in the lung non-vascular tissue early in infection, followed by a positive association at later time points. Our study is the first to demonstrate that platelets have a functionally active vRNA-sensing RIG-I receptor that finely tunes thrombotic risk and facilitates appropriate leukocyte transmigration during infection, through non-classical platelet activation.