For some genes, corticosteroid treatment is associated with a partially suppressed IFN response within each group—for instance, ciliated cells from untreated COVID-19 WHO 1–5 participants show higher abundances of IFITM1, OAS2, IFI6, and IFI27 than their corticosteroid-treated counterparts—while still maintaining strong differences in expression between severity groups (Figures S4E and S4F). Here, OAS2 is linked to COVID-19.