Up-Regulation of IL-17 Is Associated with Bioactive IL-8 Expression in Helicobacter pylori-Infected Human Gastric Mucosa1

Helicobacter pylori (Hp)-associated gastritis is characterized by an increased number of acute and chronic inflammatory cells secreting cytokines that contribute to maintain and expand the local inflammation. Locally induced IL-8 is believed to play a major role in the Hp-associated acute inflammatory response. Factors/mechanisms that regulate IL-8 induction are, however, not fully understood. In the present study we investigated whether Hp infection is associated with an increased production of IL-17, a T cell-derived cytokine capable of modulating IL-8 gene expression. We showed that both IL-17 RNA transcripts and protein were expressed at a higher level in the whole gastric mucosal and lamina propria mononuclear cell samples from Hp-infected patients than in those from uninfected subjects. Hp eradication was associated with a marked down-regulation of IL-17 expression. The addition of a neutralizing anti-IL-17 Ab to the gastric lamina propria mononuclear cell cultures resulted in a significant inhibition of IL-8 secretion, indicating that IL-17 contributes to enhance IL-8 in the Hp-colonized gastric mucosa. Consistently, stimulation of MKN 28 cells, a gastric epithelial cell line, with IL-17 increased IL-8 secretion. Finally, conditioned medium from the IL-17-stimulated MKN 28 cell cultures promoted the in vitro polymorphonuclear leukocyte migration. This effect was inhibitable by a neutralizing IL-8 but not IL-17 Ab. Together, these data indicate that biologically active IL-17 production is increased during Hp infection, suggesting the possibility that this cytokine may play an important role in the inflammatory response to the Hp colonization.