Mucosal T-cell and cytokine responses in Helicobacter pylori-infected duodenal ulcer patients

Abstract

Helicobacter pylori colonizes the human stomach and areas of gastric metaplasia in the duodenum. The bacterium is the major cause of chronic active gastritis and peptic ulcer disease and is a risk factor for the development of gastric adenocarcinoma and lymphoma. However, the majority of those infected remain asymptomatic (AS) carriers of the bacteria, and only 10-15% develop duodenal ulcers (DU). It is still unknown which factors determine whether an individual will develop duodenal ulcer disease or remain an AS carrier, but bacterial factors as well as host immune responses are believed to be important for the outcome of infection. To evaluate the role of the immune response in the development of duodenal ulcers, we compared the mucosal T-cell and cytokine responses in DU patients, AS carriers, and uninfected individuals. Immunohistochemical analysis of the duodenal cytokine responses showed similar cytokine staining in normal and metaplastic duodenal mucosa of H. pylori-infected individuals. However, decreased levels of several cytokines, i.e. IL-8, IL-6, IL-1b, IFN-g and TGF-b were observed in the epithelium of duodenal biopsies from DU patients, as compared to from AS carriers and uninfected subjects. Analysis of freshly isolated duodenal epithelial cells further confirmed this finding, i.e. significantly lower levels of IL-8 were produced by cells from DU patients than from AS carriers. This was found to be due to properties of the epithelial cells rather than apoptosis, down-regulation by other immune cells or differences in bacterial strains. In the lamina propria of the duodenum, the number of cytokine positive mononuclear cells (MNCs) was found to be up-regulated in H. pylori-infected, as compared to uninfected individuals, but with similar levels in DU patients and AS carriers. Analysis of the T-cell responses in the duodenum and the antrum of the stomach showed increased infiltration of primarily CD4+ T cells in the antrum, whereas no differences in the number of T cells were found in the duodenum of H. pylori-infected and uninfected individuals. The expression of the activation markers CD69 and CD25 was found to be significantly higher in the antrum, and slightly increased in the duodenum of both H. pylori-infected AS carriers and DU patients. Flow cytometric analysis of isolated mucosal T cells revealed increased numbers of CD4+CD25high cells, i.e. regulatory T cells (Treg) in the antrum and duodenum of H. pylori-infected individuals, as compared to uninfected subjects. CTLA-4, a marker of Treg, was found to be highly expressed in the majority of these cells. Interestingly, when comparing the numbers of down-regulating CTLA-4+ cells in the duodenum of H. pylori-infected DU patients and AS carriers by immunohistochemistry, we observed significantly increased frequencies of these cells in the duodenal mucosa of DU patients. We speculate that these cells, at least in part, are regulatory T cells that may down-regulate the specific T-cell responses in the duodenal mucosa of DU patients. In conclusion, our results show that the immune responses in the duodenum against H. pylori may be down-regulated or suppressed in DU patients and may hence not be efficient enough to clear the infection, which consequently becomes chronic and may lead to the development of duodenal ulcers.