Evaluation of the Diagnostic Value of FliD, a Helicobacter pylori Flagellar Protein

Novel immunodominant antigens are urgently required for the diagnosis and vaccination of Helicobacter pylori (HP). FliD, an important colonization factor, was cloned and expressed (rFliD) to evaluate the levels of specific immunoglobulin G (IgG), IgM, and IgA antibodies in the serum of patients using ELISA. Rabbit anti-rFliD polyclonal antibody (pAb) was obtained by the subcutaneous injection of rFliD. The rFliD-specific IFN-γ and IL-4 levels in peripheral blood mononuclear cells and CD4⁺ T cells from humans were analyzed using enzyme-linked immunospot and flow cytometry. We found that the levels of rFliD-specific IgG, IgM, and IgA were significantly higher in HP-infected-patients than in healthy controls. IgG, IgM, and IgA had diagnostic sensitivities of 92.6%, 89.8%, and 83.2%; specificities of 91.1%, 88.7%, and 64.6%; and areas under the receiver operating curves of 0.97, 0.96, and 0.92, respectively. Furthermore, rFliD-pAb was used for the immunohistochemical analysis of gastritis and gastric cancer tissues from patients infected with HP. The levels of rFliD-specific IFN-γ and IL-4 were significantly elevated in HP-infected patients and exhibited a dominant T helper type 1-dominant subtype. These findings indicate that rFliD exhibits high validity as a biomarker in HP diagnosis and may also be a potent antigen for vaccine design because of its high cellular and humoral immune responses.