Adjuvant effects of chimeric flagellin and chitosan/tripolyphosphate (CS/TPP) nanogel encapsulation on immune response induced by nasal vaccination of Helicobacter pylori adhesin

Abstract:

[Objective] H. pylori adhesin A (HpaA) is a promising antigen for Helicobacter pylori vaccine. Adjuvant effects of chimeric flagellin cFLN and chitosan/tripolyphosphate (CS/TPP) nanogel encapsulation on humoral and gastric mucosal immune response induced by nasal vaccination of HpaA was investigated. [Methods] Chimeric flagellin cFLN was constructed by combining D0 and D1 domains of Salmonella typhimurium flagellin FliC with D2 and D3 domains of Helicobacter pylori flagellin FlaA. Chimeric flagellin cFLN was then linked with adhesin (HpaA) to construct a complex antigen cFLN-HpaA. cFLN, HpaA and cFLN-HpaA was expressed in recombinant E. coli and further purified by Ni-NTA Prepacked chromatographic column. cFLN, HpaA and cFLN-HpaA were further encapsulated into chitosan/tripolyphosphate (CS/TPP) nanogels to prepare cFLN-loaded CS/TPP nanogels (cFLN NG), HpaA-loaded CS/TPP nanogels (HpaA NG), and cFLN-HpaA-loaded CS/TPP/nanogels (cFLN-HpaA NG) by an ionic gelation method. In vivo immunogenicity studies were performed with mice. [Results] cFLN, HpaA and cFLN-HpaA was successfully prepared and encapsulated within CS/TPP/nanogels. After immunizing mice through the nose, compared with HpaA, cFLN-HpaA caused a 2.09, 1.4 and 2.62-fold increase in serum IgG, IgG1 and IgA levels, respectively. Compared with cFLN, HpaA and cFLN-HpaA, cFLN NG, HpaA NG and cFLN-HpaA NG increased the serum levels of IgA, IgG, IgG1 and IgG2a by 1.28 to 1.71 times. [Conclusion] cFLN and CS/TPP NG can significantly enhance the humoral immunity induced by HpaA delivered in the nasal cavity. The contents of IFN-γ, IL-4, IL-17 and SIgA in gastric mucosa after nasal immunization were detected. Compared with HpaA, cFLN-HpaA induced a 1.38, 1.16 and 1.58-fold increase in the content of IFN-γ, IL-4 and SIgA, respectively. Compared with cFLN-HpaA, cFLN-HpaA NG increased the contents of IFN-γ, IL-4, IL-17 and SIgA in mouse gastric mucosa by 1.81, 1.71, 2.16 and 2.10 times, respectively. It shows that cFLN and CS/TPP NG can significantly enhance Th1 and Th17 immune responses. In vivo immunogenicity studies in mouse indicated that cFLN and nanogel encapsulation could effectively not only enhance hurmoral immune responses, but also gastric mucosal immune response, Th1 and Th17 type immune response in gastric mucosa induced by nasally delivered HpaA. Therefore, these results suggested that cFLN-HpaA NG might be a promising nasally delivered vaccine system for protection against Helicobacter pylori infection.