The Role Of Th17 Cells And IL-17 On Helicobacter Pylori Infection

Helicobacter pylori (H. pylori) is a Gram-negative, microaerophilic bacterium that resides extracellularly in the gastric mucosa and infects more than 50% of the population worldwide. H. pylori-induced chronic inflammation is the cause of gastritis and peptic ulcer and a risk factor for gastric cancer. H. pylori infection causes severe local inflammation in the gastric mucosa.CD3+ CD4+ T cells are increased in infected gastric lamina propria and play important roles in the pathogenesis of persistent H. pylori infection. Traditionally, CD4+ T cells, also known as T helper cells (Th cells), are classified into two main classes: Th1 and Th2, on the basis of their cytokine secretion and immune regulatory functions. Th1 cells secrete IFN-γ, IL-2, and IL-12 and regulate cellular immunity, while Th2 cells produce IL-4, IL-5, and IL-13 and mediate humoral responses. To date, studies of immune responses to H. pylori have largely focused on Th1 and Th2 cells and it is generally accepted that H. pylori infection results in a Th1-dominant response and that gastric inflammation largely depends on Th1 cell responses, however, IFN-γsecretion alone is insufficient to induce gastritis. Thus, the detailed mechanism of pathogenesis is not clear.Recently, a novel subset of effector T cells, identified by secretion of IL-17, has been defined as Th17 cells. Th17 cells are distinct from Th1 and Th2 cells in differentiation and function. Th17 cells are clearly implicated in the pathogenesis of autoimmune diseases by promoting chronic inflammation. However, the protective and pathogenic functions of IL-17-producing Th cells were both reported in infections. The identification of Th17 cells necessitates a re-evaluation of Th cell responses in H. pylori infection. However, the characteristics of Th cell responses, including those of Th1, Th2 and Th17 cells, remain unclear and the role of Th17 cell responses in H. pylori infection has not been elucidated.【Objectives】1. Try to characterize Th cell responses, especially Th17 cell responses, to H. pylori shortly after infection of a BALB/c mouse model.2. Aim to elucidate the role of Th17 cells in the early stage of H. pylori infection and explore the mechanism.【Methods】1. BALB/c mice were infected with H. pylori orally and gastric tissues were collected at the indicated times post-infection. Cytokine expression in the stomach was determined by real-time PCR and ELISA. Cell responses in spleen,mesenteric lymph node and paragastric lymph node were examined by intracellular staining for IFN-γ, IL-4 and IL-17.2. The recombinant GST-IL-17 was cloned and expressed in E. coli and were used to immunize rabbit to obtain the anti-IL-17 antibody. Before H. pylori infection, IL-17 antibody was administrated to the mice intraperitoneally and the colonization of H. pylori was measured with real-time PCR to detect the 16s rDNA of H. pylori and the gastric inflammation was assayed by H&E staining. In addition, AdmIL-17 was administrated to the mice orally before H. pylori infection to assay the effects of IL-17 on the colonization and inflammation.3. MFC cells were stimulated with commercial mIL-17, Cells were collected for analysis of MMP and chemokine mRNA expression by real-time PCR. The expression of MMP and chemokine mRNA was also detected in the IL-17 Ab or AdmIL-17 treated and H. pylori infected mouse model.【Results】1. H. pylori induced specific Th1 /Th17 cell responses1.1 Both mRNA and protein of IFN-γand IL-17 were expressed at a higher level in gastric tissue from H. pylori-infected mice than in those from control mice, whereas IL-4 expression did not change significantly in protein level. IL-23 and IL-12 were also increased in gastric tissue.1.2 Splenic lymphocytes from infected mice showed significantly higher Th1 and Th17 cell responses than those from uninfected mice when stimulated with PMA and ionomycin or H. pylori whole cell protein, whereas Th2 cell responses were not significantly changed, suggesting that specific Th1 and Th17 cell responses were induced in H. pylori infection. 1.3 Th1, Th2 and Th17 cell responses in MLN were all primed on day 7 pi. In the spleen, Th17 cells were expanded on day 14 and peaked on day 21 pi, and Th1 cells were induced from day 21 to 28 pi, whereas Th2 showed no significant change during the course of infection. The Th cell responses were delayed in PLN, reaching detectable levels on day 28 pi. The Th cell responses in spleen and PLN showed a dynamic change: Th17 cell responses preceded Th1 cell responses. The time course of Th cell responses in different organs suggests that MLN may be an earlier site of T cell priming during H. pylori infection.2. Th17/IL-17 contribute to gastric inflammation and H. pylori colonization.2.1 The colonization of H. pylori and the inflammation of gastric tissue in the anti-IL-17 Ab-treated mice was significantly lower than that in the control IgG-treated mice (P < 0.05),suggesting that the Th17/IL-17 pathway might impair host defense against H. pylori infection.2.2 Pretreatment with AdmIL-17 resulted in more copies of H. pylori in the stomach than in mice treated with AdLuc (P < 0.01), while the copies of H. pylori after AdLuc pretreatment were not different from those in PBS-treated mice (P > 0.05). In addition, mice treated with AdmIL-17 showed significantly more gastric inflammation than mice treated with AdLuc (P < 0.0125), and the inflammatory response in AdLuc-treated mice was similar to that in PBS-treated mice (P > 0.05). These results indicate that Th17/IL-17 might increase the susceptibility to H. pylori infection.3. The effect of IL-17 on expression of MMPs and chemokines3.1 The expression of MMP-2, MMP-3, MMP-7, MMP-9 and chemokine CCL2, CCL5, CCL20, CCL25 and CXCL1 in MFC cells were up-regulated by IL-17 stimulation.3.2 IL-17 Ab pretreatment reduced MMP-9 and CCL25 expression in H. pylori-infected stomachs (P < 0.05), but it had no significant effect on the expression of other factors.3.3 AdmIL-17 treatment increased MMP-2, MMP-9 and CCL25 expression compared with AdLuc-treated and PBS-treated mice (P < 0.05). The results indicate that Th17/IL-17 pathway may exert its effect on H. pylori infection by enhancing MMP-9 and CCL25 production.【Conclusion】 1. H. pylori-specific Th1/Th17 responses are induced in the BALB/c mouse model and display different dynamics. The Th cell responses occurred earlier in the mesenteric lymph node than in the spleen or paragastric lymph nodes.2. Th17/IL-17 pathway might facilitate bacterial colonization and inflammation in the early stage of H. pylori infection.3. The role of IL-17 on H. pylori infection might be associated with the expression of MMP-9 and CCL25.【significance】The Th17/IL-17 pathway might be a potential therapeutic target in H. pylori-associated diseases. Further study is required to elucidate the mechanisms by which H. pylori interacts with Th17 cells and how these cells facilitate infection. A better understanding of the nature, regulation, and function of Th cell responses to H. pylori may help to explore novel and effective immunotherapies for gastric diseases induced by this organism.