TMPRSS2 and chronic obstructive pulmonary disease: The proportion of TMPRSS2 + AT2 cells is decreased in IPF lungs while TMPRSS2 + AT1 and Transitional AT2 cells are higher in all CLD samples; and TMPRSS2 + SCGB3A2 +/SCGB1A+ club cells are in significantly higher numbers in COPD patients compared to controls (Fig. 1c).