['The MUC1 mucin is expressed on the cell surface of epithelial cells lining the gastric mucosa. Epidemiologic studies suggest that functional allelic variations in the MUC1 gene may play a role in human susceptibility to Helicobacter pylori-associated pathologies, including gastric adenocarcinoma. We have evaluated the impact of Muc1 expression on the colonization and pathogenesis of gastric Helicobacter infections.', 'Wild-type and Muc1-deficient mice were infected with H pylori and colonization and gastritis levels determined. Primary gastric cells were used to examine the impact of Muc1 expression on bacterial adherence.', 'Mice lacking Muc1 were colonized by 5-fold more H pylori within 1 day of infection, and this difference was maintained for at least 2 months postinfection. Mice heterozygous for the null Muc1 allele developed intermediate bacterial colonization. Although wild-type mice developed only a mild gastritis when infected for 2 months with H pylori, Muc1(-/-) mice developed an atrophic gastritis marked by loss of parietal cells. We demonstrate H pylori adhesion to purified MUC1 and significantly increased adhesion to cultured murine Muc1 null gastric epithelial cells, suggesting that Muc1 acts as a decoy limiting binding to the cell surface.'] Does muc1 mucin limit both Helicobacter pylori colonization of the murine gastric mucosa and associated gastritis?