KRT13 and COVID-19: The majority of secretory and goblet clusters are represented by cells from individuals with positive SARS-CoV-2 PCRs, with significant expansion of SERPINB11high secretory cells (representing a “generic” or un-differentiated secretory subtype), BPIFA1high secretory cells, and KRT24highKRT13high secretory cells (which resemble KRT13+ “hillock” cells) among cells from individuals with severe COVID-19 (Figures 2J and S2M).