Shigella invasion plasmid
antigen B (IpaB) plays an important role in causing
shigellosis. While IpaB's
protein structure, contribution to disease mechanism, and protective immunity against
Shigella infection have been well studied, the significance of individual antigenic domains, especially at the N terminus, has not been systematically characterized. In an attempt to identify IpaB
protein functional
epitopes and to construct an optimized polyvalent multiepitope fusion
antigen (MEFA) immunogen for development of a
protein-based cross protective Shigella
vaccine, in this study, we in silico identified immunodominant
B-cell epitopes from the IpaB N terminus, fused each
epitope to
carrier protein CsaB (the major subunit of enterotoxigenic Escherichia coli CS4 adhesin) for
epitope fusion
proteins, immunized mice with each
epitope fusion
protein, examined IpaB-specific antibody responses, and assessed antibody functional activity against Shigella bacterial invasion. A total of 10 B-cell continuous
epitopes were identified from IpaB N terminus, and after being fused to
carrier protein CsaB, each
epitope induced anti-IpaB
IgG responses in the intramuscularly immunized mice. While in vitro antibody invasion inhibition assays demonstrated that
antibodies derived from each identified
epitope were functional,
epitopes 1 (LAKILASTELGDNTIQAA), 2 (HSTSNILIPELKAPKSL), and 4 (QARQQKNLEFSDKI) induced
antibodies to inhibit Shigella sonnei and Shigella flexneri invasion at levels similar to those of recombinant IpaB
protein, suggesting that these three IpaB
epitopes can be used potentially as IpaB-representing
antigens to induce protective anti-IpaB
antibodies and for construction of an
epitope-based polyvalent MEFA
protein immunogen for Shigella
vaccine development. IMPORTANCE Currently, there are no effective measures for control or prevention of
Shigella infection, the most common cause of
diarrhea in children 3 to 5 years of age in developing countries. Challenges in developing
Shigella vaccines include virulence heterogeneity among species and serotypes. To overcome virulence heterogeneity challenge and to develop a
protein-based multivalent Shigella
vaccine, we targeted a panel of
virulence factors, including invasion plasmid
antigens, identified functional antigenic domains or
epitopes as representative
antigens, and applied the novel
epitope- and structure-based vaccinology platform multiepitope fusion
antigen (MEFA) to integrate functional antigenic domains or
epitopes into a backbone immunogen to produce a polyvalent immunogen for cross protective
antibodies. Identification of functional IpaB
epitopes from this study enhances our understanding of IpaB immunogenicity and allows us to directly utilize IpaB
epitopes for construction of a cross protective polyvalent Shigella immunogen and to accelerate development of a
protein-based Shigella
vaccine.