Since our results demonstrated that WNV infection of Mavs−/− mice led to decreased expression of Foxp3 compared to WT mice (Fig. 1b), likely accounting for the deficit of Treg expansion following infection with WNV (Fig. 1b)13, we next tested the role of intrinsic MAVS signaling in Treg proliferation in vitro using a standard CFSE proliferation assay. This evidence concerns the gene FOXP3 and infection.