Helicobacter pylori specific immune response induced by conservative flagellin linear B-cell epitope

Abstract

Aim: To testify the immunogenicity of a conservative B-cell linear epitope of Helicobacter pylori (H pylori) flagellin A.

Methods: Different programs were used to analyze the secondary structure, molecular hydropathy, and surface accessibility of H pylori flagellin A. Linear B-cell epitopes were estimated based on the structural and physiochemical information. Analysis of residue divergence was proposed to screen a conservative linear epitope. The 29-peptide (Pep29mer) synthesized by chemical method, including the predicted conservative B-cell epitope and a known K2d compatible T-cell epitope, was used to immunize mice, and then H pylori-specific antibodies were detected by ELISA.

Results: Based on the analyses of divergent amino acid residues, structural and physiochemical characteristics, it was strongly suggested that the short fragment NDSDGR was the core of a conservative linear epitope in flagellin A. Animals immunized by Pep29mer acquired efficient immune response. In detail, serum H pylori-specific IgA and IgG1 increased significantly in immunized group, while IgG2a only had an insignificant change. H pylori-specific IgA in gastrointestinal flushing fluid also increased significantly.

Conclusion: The conservative short fragment NDSDGR is the core of a linear B-cell epitope of flagellin A.

Figure 1

Structural and physiochemical characteristics of flagellin A. A: Sequence of antigen determinant region in the central part of flagellin A. Underlined: hydrophilic peaks; shaded: β-turn short fragment; framed: residues accessible to molecular surface with high probability; B: secondary structure of flagellin A. Long bar: α-helices; short bar: β-sheets; other residues: irregular coils.

Figure 2

ELISA measurements of antibody subtypes in mouse serum Blue: immunized group; brown: adjuvant control group; light yellow: nude mice control group. Abscissa: time for exsanguination after prime inoculation; ordinate: A value (mean±SD).

Figure 3

Titer measurements of IgG1, IgA in mice serum (A and B) and IgA in gastrointestinal fluid (C) Blue: immunized group; brown: adjuvant control group; light yellow: nude mice control group. Abscissa: dilution of mouse gastrointestinal washing fluid; ordinate, A value (mean±SD).