In a direct comparison of ciliated cells from mild or moderate to severe COVID-19, the cells from individuals with mild or moderate disease show strong upregulation of diverse anti-viral factors, including IFI44L, STAT1, IFITM1, MX1, IFITM3, OAS1, OAS2, OAS3, STAT2, TAP1, HLA-C, ADAR, XAF1, IRF1, CTSS, CTSB, and many others. Here, XAF1 is linked to COVID-19.