Parameters Underlying Successful Protection with Live Attenuated Mutants in Experimental Shigellosis

Abstract

Because the use of live attenuated mutants of Shigella spp. represents a promising approach to protection against bacillary dysentery (M. E. Etherridge, A. T. M. Shamsul Hoque, and D. A. Sack, Lab. Anim. Sci. 46: 61-66, 1996), it becomes essential to rationalize this approach in animal models in order to optimize attenuation of virulence in the vaccine candidates, as well as their route and mode of administration, and to define the correlates of protection. In this study, we have compared three strains of Shigella flexneri 5-the wild-type M90T, an aroC mutant, and a double purE aroC mutant-for their pathogenicity, immunogenicity, and protective capacity. Protection against keratoconjunctivitis, induced by wild-type M90T, was used as the protection read out in guinea pigs that were inoculated either intranasally or intragastrically. Following intranasal immunization, the aroC mutant elicited weak nasal tissue destruction compared to M90T and achieved protection correlated with high levels of local anti-lipopolysaccharide immunoglobulin A (IgA), whereas the purE aroC double mutant, which also elicited weak tissue destruction, was not protective and elicited a low IgA response. Conversely, following intragastric immunization, only the M90T purE aroC double mutant elicited protection compared to both the aroC mutant and the wild-type strain. This mutant caused mild inflammatory destruction, particularly at the level of Peyer's patches, but it persisted much longer within the tissues. This could represent an essential parameter of the protective response that, in this case, did not clearly correlate with high anti-lipopolysaccharide IgA titers.

IL-8 Is a Key Chemokine Regulating Neutrophil Recruitment in a New Mouse Model ofShigella-Induced Colitis

“…Indeed, in a rabbit model of Shigella-induced ileitis (7), neutralization of IL-8 by an anti-IL-8 mAb, almost completely abrogates the pathological process. In the guinea pig, a species that, like the rabbit, expresses IL-8, intragastric inoculation of the invasive M90T strain induces an ileitis with some PMN recruitment (8). In addition, in human epithelial cells, invasive Shigella induce the activation of the NF-B system through Nod 1 (9), a peptidoglycan sensor (10,11), thereby promoting massive expression of IL-8 (12).…”

Analysis of Virulence and Inflammatory Potential of Shigella flexneri Purine Biosynthesis Mutants

“…In the last few years encouraging progress has been made in this regard, and a number of Shigella vaccine candidates have been constructed and evaluated based on rational attenuation of virulence. These candidates encompass mutants harboring mutations in metabolic pathways (1,6,20,40) and/or mutations in virulence genes (10,18,28,33,41). The rationale underlying these constructions is to reduce the multiplication of shigellae within the host cells and tissues along with their ability to spread or to induce specific damages.…”

New Animal Model of Shigellosis in the Guinea Pig: Its Usefulness for Protective Efficacy Studies

“…To overcome this hurdle, considerable effort over the years has been devoted to establishing a reliable animal model of bacillary dysentery. Several established Shigella infection models have proven to be useful; for instance, the pneumonia model by intranasal challenge in mice, keratoconjunctivitis by eye infection in guinea pig, intestinal inflammation by ileal ligated loop assay in rabbit, and typical bacillary dysentery following intragastric inoculation in macaques monkeys (15)(16)(17)(18)(19). However, these models are not sufficiently reliable, clinically relevant, or cost effective to be used in the screening for Shigella vaccine candidates.…”