For example, RFX2 and RFX3 showed high activity in ciliated cells regardless of disease severity, while XBP1, NR2F6, SPDEF, and ELF3 were preferentially activated in goblet cells in patients with severe COVID-19, and KLF5 and STAT2 were coactivated in patients with mild/moderate COVID-19. The gene discussed is KLF5; the disease is COVID-19.