Immunization with recombinant FliD confers protection against Helicobacter pylori infection in mice

Nearly half of the world's population is infected with Helicobacter pylori. Clinical manifestations of this infection range from gastritis and peptic ulcers to gastric adenocarcinoma and lymphoma. Due to the emerging of antibiotic resistant strains and poor patient compliance of the antibiotic therapy, there is increasing interest in the development of a protective vaccine against H. pylori infection. The bacterial protein FliD forms a capping structure on the end of each flagellum which is critical to prevent depolymerization and structural degradation. In this study, the potential of FliD as a prospective H. pylori subunit vaccine was assessed. For this purpose, immunogenicity and protective efficacy of recombinant FliD (rFliD) from H. pylori was evaluated in C57BL/6 mice. Purified rFliD was formulated with different adjuvants and administered via subcutaneous or oral route. Subcutaneous immunization with rFliD elicited predominantly mixed Th1 and Th17 immune responses, with high titers of specific IgG1 and IgG2a. Splenocytes of immunized mice exhibited strong antigen-specific memory responses, resulting in the secretion of high amounts of IFN-γ and IL-17, and low levels of IL-4. Immunization with rFliD caused a significant reduction in H. pylori bacterial load relative to naïve control mice (p < 0.001), demonstrating a robust protective effect. Taken together, these results suggest that subcutaneous vaccination with rFliD formulated with CpG or Addavax could be considered as a potential candidate for the development of a subunit vaccine against H. pylori infection.