Expression of LL-37 by human gastric epithelial cells as a potential host defense mechanism against Helicobacter pylori

Background & Aims: LL-37/human cationic antimicrobial peptide 18 (hCAP18) is a human cathelicidin with broad-spectrum antimicrobial, lipopolysaccharide binding, and chernotactic activities. This study examined the role of LL-37/hCAP18 in gastric innate immune defense by characterizing its constitutive and regulated expression by human gastric mucosa and its bactericidal activity against the gastric pathogen Helicobacter pylori. Methods: LL-37/hCAP18 messenger RNA expression in normal and H. pylori-infected gastric mucosa and gastric epithelial cells was determined by in situ hybridization, real-time polymerase chain reaction, immunostaining, and immunoblot analysis. Bactericidal activity was measured by using a colony-forming unit assay. Results: LL-37/hCAP18 messenger RNA and protein were expressed in a distinct distribution by surface epithelial cells as well as chief and parietal cells in the fundic glands of normal gastric mucosa. LL-37/hCAP18 was significantly increased in the epithelium and gastric secretions of H. pylori-infected patients, but not in individuals with non-H. pylori-induced gastric inflammation. Infection of cultured gastric epithelial cells with a wildtype but not an isogenic DeltacagE mutant strain of H. pylori increased LL-37/hCAP18 expression, indicating that H. pylori-induced regulation of LL-37/hCAP18 production required an intact type IV secretion system. LL-37, the C-terminal peptide of LL-37/hCAP18, alone or in synergy with human beta-defensin 1, was bactericidal for several H. pylori strains. Conclusions: These data indicate that H. pylori up-regulates production of LL-37/hCAP18 by gastric epithelium and suggest this cathelicidin contributes to determining the balance between host mucosal defense and H. pylori survival mechanisms that govern chronic infection with this gastric pathogen.