IRF9 and lichen planopilaris: The interferon-responsive signature genes upregulated in LPP include type II interferon (IFNγ)-responsive genes (IRF1, TAP1, IFITM1, PSMB8, IFI35, and IRF9) and type I interferon (IFNα)-responsive genes (IFIT1, OAS1, IFITM1, MX1, IFIT3, IRF9, IFI35, and PSMB8), as shown in Figure 4I and Table S2.