Acute phase T cell help in neutrophil-mediated clearance of Helicobacter pylori.

摘要

Helicobacter pylori is a bacterium that inhabits the gastric mucosa and may cause ulcers and cancer. A vaccine is desirable because treatments are complex and impractical for endemic areas. CD4+ T cells are necessary for protection in mouse vaccination models, but little is known about which immune cells kill the bacteria and how T cells may mediate this. We therefore investigated a possible IL-17-CXC chemokine pathway of neutrophil recruitment and the requirement of neutrophils for protection. We stimulated CD4+ splenocytes with H. pylori-pulsed antigen presenting cells and analyzed supernatants for IL-17. We then treated cell populations with IL-17 to evaluate their production of KC, MIP-2, and LIX. Stomach biopsies were analyzed for bacterial load, inflammation, T cells, neutrophils, and cytokines in a kinetic study of days 1-13 post-infection. Additionally, we used IL-17, IL-17R, and CXCR2 knockout mice in immunization studies and performed an in vivo neutrophil depletion with immunized/challenged G-CSF-/- mice. We observed a robust IL-17 response in vitro with stimulated CD4+ cells, and IL-17 treatment of fibroblasts and epithelial cells induced KC and LIX secretion. Likewise, there were significant T cells and IL-17 expression beginning at day 3 in the kinetic study for immunized/challenged mice. There were significantly higher mRNA levels of KC, MIP-2, and LIX in immunized mice for days 5-13. Immunized mice had significantly higher inflammation and neutrophils by day 5, preceding the significantly lower bacterial load by day 7. Surprisingly, we did not observe changes in protection in our immunized IL-17-/- and IL-17R-/- mice. Immunized CXCR2-/- mice were also protected from infection but did have significant gastric neutrophil infiltration. The depletion of neutrophils from G-CSF-/- mice resulted in decreased peripheral and gastric neutrophils and in significantly elevated bacterial load. In conclusion, we observed a robust IL-17 response in our immunization model, and IL-17 induced a strong chemokine response for neutrophil recruitment. This cytokine alone, however, was not required for protection. Our findings suggest that there are compensatory mechanisms for protection and neutrophil recruitment in the absence of an IL-17-CXC chemokine pathway but that neutrophils do contribute significantly to bacterial clearance.