The function of MUC5AC (mucin 5AC, oligomeric mucus/gel-forming, Ensembl gene identifier ENSG00000215182) is as follows. Gel-forming glycoprotein of gastric and respiratory tract epithelia that protects the mucosa from infection and chemical damage by binding to inhaled microorganisms and particles that are subsequently removed by the mucociliary system (PubMed:14535999, PubMed:14718370). Interacts with H.pylori in the gastric epithelium, Barrett's esophagus as well as in gastric metaplasia of the duodenum (GMD) (PubMed:14535999). {ECO:0000269|PubMed:14535999, ECO:0000303|PubMed:14535999, ECO:0000303|PubMed:14718370}.