Avaliação do potencial vacinal de peptídeos de antígenos de Shigella spp

Abstract

Shigellosis is a diarrheal disease that mainly affects children under 5, caused by a Gram-negative and enteroinvasive bacterium called Shigella. Mice are among the most commonly used animal models for assessing the immune response of this pathogen, due to their similarity to intestinal responses when they are subjected to infection. As no shigellosis vaccine is available yet, synthetic peptide vaccines are proposed as an alternative, which are produced from amino acid sequences of bacterial proteins and are synthesized in the laboratory. Thus, this study aimed to immunize mice from the BALB/c line through the intraperitoneal route with synthetic peptides that were designed from immunodominant epitopes of the outer membrane surface proteins of Shigella spp., called OmpC, OmpA and FimH, and then subjected them to challenge infection with a lethal dose of a virulent bacterial strain - S. flexneri 5a M90T, to estimate the protective capacity of the peptides, thus simulating the idea of a vaccine. The production of anti-peptide antibodies was analyzed by means of the Indirect ELISA immunoenzymatic assay, and the evaluation of the recognition of these antibodies in the native proteins present in the Shigella species was performed by Flow Cytometry. After challenge infection, the mice were observed for weight and survival, and the post-challenge cytokine secretion pattern was assessed by CBA (Cytometric Bead Array). The results demonstrated that all groups of peptides tested showed to be immunogenic in the first step of immunization with them in mice, as well as recognition of the antibodies in S. flexneri, S. boydii and S. dysenteriae proteins before and after challenge with M90T. All mice belonging to the selected peptide groups survived after the challenging infection, but the mice in the Peptide 1 and Pool- groups did not recover the initial weight. The peptide 2 group stood out among the others in the evaluation of the post-challenge cytokines by the equilibrium observed among them, thus suggesting a regulation of the immune system of the mice. Thus, among all the peptides tested in this study, P2 is indicated as the most effective in the intraperitoneal route, because it has been shown to be both immunogenic and an effective protector in Shigella infection, which favors it being a good vaccine candidate for shigellosis.