TMPRSS2 and chronic obstructive pulmonary disease: While the percentage of cells co-expressingACE2 and priming proteases (TMPRSS2, CTSL, FURIN) was similar across disease subtypes, there was a significantly higher number of cells co-expressingACE2 and FURIN in the COPD AT2 and Transitional AT2 cells (Fig. 1e, Supplementary Fig. 4).