Vaccine-Induced Immunity against Helicobacter pylori Infection Is Impaired in IL-18-Deficient Mice

Abstract

Protective immunity against Helicobacter pylori infection in mice has been associated with a strong Th1 response, involving IL-12 as well as IFN-γ, but recent studies have also demonstrated prominent eosinophilic infiltration, possibly linked to local Th2 activity in the gastric mucosa. In this study we investigated the role of IL-18, because this cytokine has been found to be a coregulator of Th1 development as well as involved in Th2-type responses with local eotaxin production that could influence gastric eosinophilia and resistance to infection. We found that IL-18−/− mice failed to develop protection after oral immunization with H. pylori lysate and cholera toxin adjuvant, indicating an important role of IL-18 in protection. Well-protected C57BL/6 wild-type (WT) mice demonstrated substantial influx of CD4+ T cells and eosinophilic cells in the gastric mucosa, whereas IL-18−/− mice had less gastritis, few CD4+ T cells, and significantly reduced numbers of eosinophilic cells. T cells in well-protected WT mice produced increased levels of IFN-γ and IL-18 to recall Ag. By contrast, unprotected IL-18−/− mice exhibited significantly reduced gastric IFN-γ and specific IgG2a Ab levels. Despite differences in gastric eosinophilic cell infiltration, protected WT and unprotected IL-18−/− mice had comparable levels of local eotaxin, suggesting that IL-18 influences protection via Th1 development and IFN-γ production rather than through promoting local production of eotaxin and eosinophilic cell infiltration.