Impact of O-Acetylation on 1b and 2a O-Antigen Immunogenicity in Mice.

Shigellosis is a diarrheal disease caused prevalently by and and representing a major global health risk, particularly in developing countries. Bacterial O-antigen (OAg) is the primary target of the host immune response and modifications of its oligosaccharide units, including O-acetylation, are responsible for the variability among the circulating serotypes. No vaccines are widely available against shigellosis and the understanding of the immunogenicity induced by the OAg is fundamental for the design of a vaccine that could cover the most prevalent serotypes. To understand whether a different O-acetylation pattern could influence the immune response elicited by OAg, we employed as a vaccine technology GMMA purified from 2a and 1b strains that were easily engineered to obtain differently O-acetylated OAg. Resulting GMMA were tested in mice, demonstrating not only no major impact of O-acetyl decorations on the immune response elicited by the two OAg against the homologous strains, but also that the O-acetylation of the Rhamnose III residue (O-factor 9), shared among serotypes 1b, 2a and 6, does not induce cross-reactive antibodies against these serotypes. This work contributes to the optimization of vaccine design against , providing indication about the ability of shared epitopes to elicit broad protection against serotypes and supporting the identification of critical quality attributes of OAg-based vaccines.