IL13 and cystic fibrosis: Furthermore, EHF promotes expression of Sam Pointed‐Domain Containing ETS Transcription Factor (SPDEF),12 which is involved in interleukin 13 (IL‐13)‐mediated goblet cell differentiation.58 Enhanced goblet cell differentiation increases expression of the mucin 5AC (MUC5AC) gene,59, 60 which encodes one of the major secreted mucins in the lung (reviewed in61) and is a hallmark of CF lung disease.