To address the specific feature of excess extracellular mucin production, we determined the differential expression of MUC-2, a mucin with gel-forming physicochemical properties similar to those exhibited by PMP (Kim and Gum, 1995), as well as interleukin-9 (IL-9) and its receptor (IL-9Rα), as IL-9 has been implicated in mucin-producing conditions such as cystic fibrosis (Hauber et al, 2003) and asthma (Louahed et al, 2000). This evidence concerns the gene MUC5AC and cystic fibrosis.