In vitro, Stat1 knockdown in cultured mouse PMVECs decreased antigen-presentation molecules (B2M, H2-Kb, Tap1, CD40) and IFN II pathway genes (Stat1, and Irf1) (Extended Data Fig. 8c); IFNγ treatment or H1N1 infection strongly upregulated these genes (Fig. 6g) and endothelial-specific Ifngr1 knockout (Ifngr1EC-cKO) mice showed reduced Stat1 activation and lower MHC-I and antigen-processing genes following infection (Fig. 6h). Here, IRF1 is linked to infection.