Expression of known ionocyte markers FOXI1, ASCL3, PDE1C, TFCP2L1 and CFTR in single cells was lost in hBECs from patients with neutrophilic asthma (and reduced in paucigranulocytic asthma) compared to healthy donors or eosinophilic asthma (Figures 2, 3 and Figure S3 in the Supporting Information). Here, PDE1C is linked to asthma.