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Virulence, inflammatory potential, and adaptive immunity induced by Shigella flexneri msbB mutants.

ABSTRACT: The ability of genetically detoxified lipopolysaccharide (LPS) to stimulate adaptive immune responses is an ongoing area of investigation with significant consequences for the development of safe and effective bacterial vaccines and adjuvants. One approach to genetic detoxification is the deletion of genes whose products modify LPS. The msbB1 and msbB2 genes, which encode late acyltransferases, were deleted in the Shigella flexneri 2a human challenge strain 2457T to evaluate the virulence, inflammatory potential, and acquired immunity induced by strains producing underacylated lipid A. Consistent with a reduced endotoxic potential, S. flexneri 2a msbB mutants were attenuated in an acute mouse pulmonary challenge model. Attenuation correlated with decreases in the production of proinflammatory cytokines and in chemokine release without significant changes in lung histopathology. The levels of specific proinflammatory cytokines (interleukin-1beta [IL-1beta], macrophage inflammatory protein 1alpha [MIP-1alpha], and tumor necrosis factor alpha [TNF-alpha]) were also significantly reduced after infection of mouse macrophages with either single or double msbB mutants. Surprisingly, the msbB double mutant displayed defects in the ability to invade, replicate, and spread within epithelial cells. Complementation restored these phenotypes, but the exact nature of the defects was not determined. Acquired immunity and protective efficacy were also assayed in the mouse lung model, using a vaccination-challenge study. Both humoral and cellular responses were generally robust in msbB-immunized mice and afforded significant protection from lethal challenge. These data suggest that the loss of either msbB gene reduces the endotoxicity of Shigella LPS but does not coincide with a reduction in protective immune responses.

SUBMITTER: Ranallo RT

PROVIDER: S-EPMC2798193 | biostudies-other | 2010 Jan

REPOSITORIES: biostudies-other

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Virulence, inflammatory potential, and adaptive immunity induced by Shigella flexneri msbB mutants.

Ranallo Ryan T RT Kaminski Robert W RW George Tonia T Kordis Alexis A AA Chen Qing Q Szabo Kathleen K Venkatesan Malabi M MM

Infection and immunity 20091102 1

The ability of genetically detoxified lipopolysaccharide (LPS) to stimulate adaptive immune responses is an ongoing area of investigation with significant consequences for the development of safe and effective bacterial vaccines and adjuvants. One approach to genetic detoxification is the deletion of genes whose products modify LPS. The msbB1 and msbB2 genes, which encode late acyltransferases, were deleted in the Shigella flexneri 2a human challenge strain 2457T to evaluate the virulence, infla ...[more]

PMID: 19884336

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Project description:Shigella flexneri is an intracellular human pathogen that invades colonic cells and causes bloody diarrhea. S. flexneri evolved from commensal Escherichia coli, and genome comparisons reveal that S. flexneri has lost approximately 20% of its genes through the process of pathoadaptation, including a disproportionate number of genes associated with the turnover of the nucleotide-based second messenger cyclic di-GMP (c-di-GMP); however, the remaining c-di-GMP turnover enzymes are highly conserved. c-di-GMP regulates many behavioral changes in other bacteria in response to changing environmental conditions, including biofilm formation, but this signaling system has not been examined in S. flexneri. In this study, we expressed VCA0956, a constitutively active c-di-GMP synthesizing diguanylate cyclase (DGC) from Vibrio cholerae, in S. flexneri to determine if virulence phenotypes were regulated by c-di-GMP. We found that expressing VCA0956 in S. flexneri increased c-di-GMP levels, and this corresponds with increased biofilm formation and reduced acid resistance, host cell invasion, and plaque size. We examined the impact of VCA0956 expression on the S. flexneri transcriptome and found that genes related to acid resistance were repressed, and this corresponded with decreased survival to acid shock. We also found that individual S. flexneri DGC mutants exhibit reduced biofilm formation and reduced host cell invasion and plaque size, as well as increased resistance to acid shock. This study highlights the importance of c-di-GMP signaling in regulating S. flexneri virulence phenotypes. IMPORTANCE The intracellular human pathogen Shigella causes dysentery, resulting in as many as one million deaths per year. Currently, there is no approved vaccine for the prevention of shigellosis, and the incidence of antimicrobial resistance among Shigella species is on the rise. Here, we explored how the widely conserved c-di-GMP bacterial signaling system alters Shigella behaviors associated with pathogenesis. We found that expressing or removing enzymes associated with c-di-GMP synthesis results in changes in Shigella's ability to form biofilms, invade host cells, form lesions in host cell monolayers, and resist acid stress.

Dataset Information

Virulence, inflammatory potential, and adaptive immunity induced by Shigella flexneri msbB mutants.

Publications

Virulence, inflammatory potential, and adaptive immunity induced by Shigella flexneri msbB mutants.

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