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Updated: Jul 5, 2026
Epithelial Cell Infection Analyses with Shigella
Published on: February 9, 2024
Immunological evidence for functional rather than structural mimicry by a Shigella flexneri Y polysaccharide-mimetic
Silvia Borrelli1, Rehana B Hossany, B Mario Pinto
1Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
Abstract:
An approach to vaccine design is the use of molecules that mimic the immunogenic element of interest. In this context, the interaction of MDWNMHAA, a peptide mimic of the Shigella flexneri Y O polysaccharide (PS), with an anti-carbohydrate monoclonal antibody, as studied previously by X-ray crystallography, suggested the presence of functional rather than structural mimicry and a bound peptide conformation that was not represented significantly in the free-ligand ensemble. The antibody response elicited by an MDWNMHAA-carrier protein (tetanus toxoid [TT]) conjugate has now been investigated in BALB/c mice. The mice were immunized following a homologous prime/boost strategy using MDWNMHAA-TT as the immunogen. The mice showed anti-peptide antibody (immunoglobulin G [IgG]) titers that increased after being boosted. High anti-lipopolysaccharide (LPS) (IgG) titers were observed after the last boost. A faster immune response, with cross-reactive titers, was observed with a peptide conjugate with 30% more copies of the peptide. The binding of anti-peptide polyclonal antibodies to LPS could be inhibited by LPS, PS, MDWNMHAA, and MDWNMHAA-bovine serum albumin, as assessed by inhibition enzyme-linked immunosorbent assay. Conversely, mice immunized with PS-TT showed IgG anti-peptide titers. These data demonstrate the cross-reactivity of the antibody response and support the hypothesis that functional, as opposed to structural, mimicry of the S. flexneri Y O PS by MDWNMHAA or the underrepresentation of the bound ligand conformation in the free-ligand ensemble does not compromise immunological cross-reactivity. Prime/boost strategies were performed with a heterologous boost of PS-TT or MDWNMHAA-TT. They led to high anti-LPS titers after only three injections, suggesting alternatives to improve the immunogenicity of the carbohydrate-mimetic peptide and confirming the antigenic mimicry.
Insights
This study shows that a peptide mimic (MDWNMHAA) of Shigella flexneri Y O polysaccharide successfully elicits antibodies. These antibodies cross-react with the target polysaccharide, supporting functional mimicry for vaccine development.
Area of Science:
- Immunology
- Vaccine Design
- Microbial Pathogenesis
Background:
- Vaccine development often employs molecular mimics of pathogenic antigens.
- A peptide mimic, MDWNMHAA, of Shigella flexneri Y O polysaccharide (PS) was previously studied.
- X-ray crystallography suggested functional rather than structural mimicry by MDWNMHAA.
Purpose of the Study:
- To investigate the antibody response elicited by a conjugate of MDWNMHAA and tetanus toxoid (TT) in mice.
- To assess the immunological cross-reactivity between the peptide mimic and the native polysaccharide.
Main Methods:
- BALB/c mice were immunized with MDWNMHAA-TT conjugate using a homologous prime/boost strategy.
- Antibody titers (IgG) against peptide and lipopolysaccharide (LPS) were measured.
- Inhibition enzyme-linked immunosorbent assays were used to assess antibody binding specificity.
Main Results:
- Immunization with MDWNMHAA-TT induced significant anti-peptide and anti-LPS IgG titers.
- A conjugate with increased peptide density accelerated the immune response and cross-reactivity.
- Antibodies generated against the peptide also bound to LPS, and this binding was inhibited by LPS, PS, and the peptide.
Conclusions:
- The study supports functional mimicry of S. flexneri Y O PS by MDWNMHAA.
- Underrepresentation of bound conformation in free-ligand ensemble did not impede immunological cross-reactivity.
- Optimized prime/boost strategies with peptide conjugates can lead to high anti-LPS titers, confirming antigenic mimicry.
