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An NK Cell Perforin Response Elicited via IL-18 Controls Mucosal Inflammation Kinetics during Salmonella Gut Infection.

Müller AA, Dolowschiak T, Sellin ME, Felmy B, Verbree C, Gadient S, Westermann AJ, Vogel J, LeibundGut-Landmann S, Hardt WD - PLoS Pathog. (2016)

Bottom Line: IL-18 boosted NK cell chemoattractants and enhanced the NK cells' migratory capacity, thus promoting mucosal accumulation of mature, activated NK cells.NK cell depletion and Prf-/- ablation (but not granulocyte-depletion or T-cell deficiency) delayed tissue inflammation.This may have broad relevance for mucosal defense against microbial pathogens.

View Article: PubMed Central - PubMed

Affiliation: Institute of Microbiology, ETH Zürich, Zürich, Switzerland.

ABSTRACT
Salmonella Typhimurium (S.Tm) is a common cause of self-limiting diarrhea. The mucosal inflammation is thought to arise from a standoff between the pathogen's virulence factors and the host's mucosal innate immune defenses, particularly the mucosal NAIP/NLRC4 inflammasome. However, it had remained unclear how this switches the gut from homeostasis to inflammation. This was studied using the streptomycin mouse model. S.Tm infections in knockout mice, cytokine inhibition and -injection experiments revealed that caspase-1 (not -11) dependent IL-18 is pivotal for inducing acute inflammation. IL-18 boosted NK cell chemoattractants and enhanced the NK cells' migratory capacity, thus promoting mucosal accumulation of mature, activated NK cells. NK cell depletion and Prf-/- ablation (but not granulocyte-depletion or T-cell deficiency) delayed tissue inflammation. Our data suggest an NK cell perforin response as one limiting factor in mounting gut mucosal inflammation. Thus, IL-18-elicited NK cell perforin responses seem to be critical for coordinating mucosal inflammation during early infection, when S.Tm strongly relies on virulence factors detectable by the inflammasome. This may have broad relevance for mucosal defense against microbial pathogens.

No MeSH data available.


Related in: MedlinePlus

Perforin-deficient mice fail to elicit overt gut inflammation by 12h p.i.(a and b) Prf1-/- mice and littermate controls were Sm-pretreated and infected orally with 5x107 CFU S.Tm for 12h. (a) Pathological score; arrows indicate representative mice depicted in panel b, (b) HE-stained cryosections from representative mice of each group. (c) Il18-/- mice and littermates or (d) Prf1-/- mice and littermates were Sm-pretreated and infected orally with 5x107 CFU S.Tm-pssaG-GFPmut2 for 12h (n = 4–6 per group). S.Tm cecum tissue counts were determined per 20μm cross-section. Statistical analysis was performed using the Mann-Whitney-U test (** = p<0.01).
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ppat.1005723.g007: Perforin-deficient mice fail to elicit overt gut inflammation by 12h p.i.(a and b) Prf1-/- mice and littermate controls were Sm-pretreated and infected orally with 5x107 CFU S.Tm for 12h. (a) Pathological score; arrows indicate representative mice depicted in panel b, (b) HE-stained cryosections from representative mice of each group. (c) Il18-/- mice and littermates or (d) Prf1-/- mice and littermates were Sm-pretreated and infected orally with 5x107 CFU S.Tm-pssaG-GFPmut2 for 12h (n = 4–6 per group). S.Tm cecum tissue counts were determined per 20μm cross-section. Statistical analysis was performed using the Mann-Whitney-U test (** = p<0.01).

Mentions: Besides the production of pro-inflammatory cytokines, NK cells can exert their effector function by inducing cell death of target cells [41], either by inducing target cell apoptosis by death ligand signaling via TRAIL or FasL or by releasing cytotoxic granules, containing proteases called granzymes and perforins [56–58]. IL-18 can prime this cytotoxicity [59]. Upon release of the granules in close proximity to the target cell, perforin forms pores in the plasma membrane, enabling granzyme uptake into the target cell and subsequent induction of apoptotic cell death or osmotic cell lysis. These mechanisms are well known to eliminate virus-infected host cells [60]. A role in bacterial infections in vivo (i.e. liver infection by Chromobacterium violaceum and Citrobacter rodentium infection in the colon) has only recently been identified [6, 61]. Other systemic infections by intracellular pathogens (e.g. S.Tm, Listeria monocytogenes) are not affected in perforin-deficient mice, presumably due to down-regulation of inflammasome/IL-18 stimulating ligands at these sites [6, 39, 62]. However, it remained unclear if NK-cell mediated cytotoxicity might be involved in the initial phases of S.Tm gut infection. Based on the increased levels of mature IL-18 in the infected mucosa (Fig 1a) and the accumulation of matured NK-cells by 12h p.i., we hypothesized that this might indeed be the case. To this end, we infected perforin-deficient animals and littermate controls for 12h (5x107 CFU S.Tm by gavage) and assessed cecal pathology. Strikingly, perforin-deficient mice showed a much lower degree of mucosal pathology than their littermate controls (Fig 7a and 7b, S6b Fig ), while luminal pathogen loads were not affected (S6a Fig). In fact, perforin-deficiency fully recapitulated the delayed mucosal pathology observed in IL-18-deficient mice and NK cell-depleted animals (compare Fig 7a to Figs 1b and 2m). This provided a first hint suggesting that perforin is an important NK cell effector mechanism that accelerates disease kinetics in the early phase of S.Tm infection.


An NK Cell Perforin Response Elicited via IL-18 Controls Mucosal Inflammation Kinetics during Salmonella Gut Infection.

Müller AA, Dolowschiak T, Sellin ME, Felmy B, Verbree C, Gadient S, Westermann AJ, Vogel J, LeibundGut-Landmann S, Hardt WD - PLoS Pathog. (2016)

Perforin-deficient mice fail to elicit overt gut inflammation by 12h p.i.(a and b) Prf1-/- mice and littermate controls were Sm-pretreated and infected orally with 5x107 CFU S.Tm for 12h. (a) Pathological score; arrows indicate representative mice depicted in panel b, (b) HE-stained cryosections from representative mice of each group. (c) Il18-/- mice and littermates or (d) Prf1-/- mice and littermates were Sm-pretreated and infected orally with 5x107 CFU S.Tm-pssaG-GFPmut2 for 12h (n = 4–6 per group). S.Tm cecum tissue counts were determined per 20μm cross-section. Statistical analysis was performed using the Mann-Whitney-U test (** = p<0.01).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920399&req=5

ppat.1005723.g007: Perforin-deficient mice fail to elicit overt gut inflammation by 12h p.i.(a and b) Prf1-/- mice and littermate controls were Sm-pretreated and infected orally with 5x107 CFU S.Tm for 12h. (a) Pathological score; arrows indicate representative mice depicted in panel b, (b) HE-stained cryosections from representative mice of each group. (c) Il18-/- mice and littermates or (d) Prf1-/- mice and littermates were Sm-pretreated and infected orally with 5x107 CFU S.Tm-pssaG-GFPmut2 for 12h (n = 4–6 per group). S.Tm cecum tissue counts were determined per 20μm cross-section. Statistical analysis was performed using the Mann-Whitney-U test (** = p<0.01).
Mentions: Besides the production of pro-inflammatory cytokines, NK cells can exert their effector function by inducing cell death of target cells [41], either by inducing target cell apoptosis by death ligand signaling via TRAIL or FasL or by releasing cytotoxic granules, containing proteases called granzymes and perforins [56–58]. IL-18 can prime this cytotoxicity [59]. Upon release of the granules in close proximity to the target cell, perforin forms pores in the plasma membrane, enabling granzyme uptake into the target cell and subsequent induction of apoptotic cell death or osmotic cell lysis. These mechanisms are well known to eliminate virus-infected host cells [60]. A role in bacterial infections in vivo (i.e. liver infection by Chromobacterium violaceum and Citrobacter rodentium infection in the colon) has only recently been identified [6, 61]. Other systemic infections by intracellular pathogens (e.g. S.Tm, Listeria monocytogenes) are not affected in perforin-deficient mice, presumably due to down-regulation of inflammasome/IL-18 stimulating ligands at these sites [6, 39, 62]. However, it remained unclear if NK-cell mediated cytotoxicity might be involved in the initial phases of S.Tm gut infection. Based on the increased levels of mature IL-18 in the infected mucosa (Fig 1a) and the accumulation of matured NK-cells by 12h p.i., we hypothesized that this might indeed be the case. To this end, we infected perforin-deficient animals and littermate controls for 12h (5x107 CFU S.Tm by gavage) and assessed cecal pathology. Strikingly, perforin-deficient mice showed a much lower degree of mucosal pathology than their littermate controls (Fig 7a and 7b, S6b Fig ), while luminal pathogen loads were not affected (S6a Fig). In fact, perforin-deficiency fully recapitulated the delayed mucosal pathology observed in IL-18-deficient mice and NK cell-depleted animals (compare Fig 7a to Figs 1b and 2m). This provided a first hint suggesting that perforin is an important NK cell effector mechanism that accelerates disease kinetics in the early phase of S.Tm infection.

Bottom Line: IL-18 boosted NK cell chemoattractants and enhanced the NK cells' migratory capacity, thus promoting mucosal accumulation of mature, activated NK cells.NK cell depletion and Prf-/- ablation (but not granulocyte-depletion or T-cell deficiency) delayed tissue inflammation.This may have broad relevance for mucosal defense against microbial pathogens.

View Article: PubMed Central - PubMed

Affiliation: Institute of Microbiology, ETH Zürich, Zürich, Switzerland.

ABSTRACT
Salmonella Typhimurium (S.Tm) is a common cause of self-limiting diarrhea. The mucosal inflammation is thought to arise from a standoff between the pathogen's virulence factors and the host's mucosal innate immune defenses, particularly the mucosal NAIP/NLRC4 inflammasome. However, it had remained unclear how this switches the gut from homeostasis to inflammation. This was studied using the streptomycin mouse model. S.Tm infections in knockout mice, cytokine inhibition and -injection experiments revealed that caspase-1 (not -11) dependent IL-18 is pivotal for inducing acute inflammation. IL-18 boosted NK cell chemoattractants and enhanced the NK cells' migratory capacity, thus promoting mucosal accumulation of mature, activated NK cells. NK cell depletion and Prf-/- ablation (but not granulocyte-depletion or T-cell deficiency) delayed tissue inflammation. Our data suggest an NK cell perforin response as one limiting factor in mounting gut mucosal inflammation. Thus, IL-18-elicited NK cell perforin responses seem to be critical for coordinating mucosal inflammation during early infection, when S.Tm strongly relies on virulence factors detectable by the inflammasome. This may have broad relevance for mucosal defense against microbial pathogens.

No MeSH data available.


Related in: MedlinePlus