PLoS One. 2013 Dec 2;8(12):e80656

A Balanced IL-1β Activity is Required for Host Response to Citrobacter rodentium Infection

Misagh Alipour*, Yuefei Lou*, Daniel Zimmerman, Michael W. Bording-Jorgensen, Consolato Sergi, Julia J. Liu, Eytan Wine

*These authors contributed equally.

Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada ; Centre of Excellence for Gastrointestinal Inflammation and Immunity Research (CEGIIR), University of Alberta, Edmonton, Alberta, Canada.

Corresponding author: Eytan Wine, MD, PhD; Department of Pediatrics, University of Alberta, Edmonton, AB, T6G 2E1, Canada; Phone: 780-248-5420; Email: wine@ualberta.ca

 

ABSTRACT

Background: Microbial sensing plays essential roles in the innate immune response to pathogens. In particular, NLRP3 forms a multiprotein inflammasome complex responsible for the maturation of interleukin (IL)-1β. Our aim was to delineate the role of the NLRP3 inflammasome in macrophages, and the contribution of IL-1β to the host defense against Citrobacter rodentium acute infection in mice.

Methods: Nlrp3-/- and background C57BL/6 (WT) mice were infected by orogastric gavage, received IL-1β (0.5 µg/mouse; ip) on 0, 2, and 4 days post-infection (DPI), and assessed on 6 and 10 DPI.

Results: Infected Nlrp3-/- mice developed severe colitis; IL-1β treatments reduced colonization, abrogated dissemination of bacteria to mesenteric lymph nodes, and protected epithelial integrity of infected Nlrp3-/- mice. In contrast, IL-1β treatments of WT mice had an opposite effect with increased penetration of bacteria and barrier disruption. Microscopy showed reduced damage in Nlrp3-/- mice, and increased severity of disease in WT mice with IL-1β treatments, in particular on 10 DPI. Secretion of some pro-inflammatory plasma cytokines was dissipated in Nlrp3-/- compared to WT mice. IL-1β treatments elevated macrophage infiltration into infected crypts in Nlrp3-/- mice, suggesting that IL-1β may improve macrophage function, as exogenous administration of IL-1β increased phagocytosis of C. rodentium by peritoneal Nlrp3-/- macrophages in vitro. As well, the exogenous administration of IL-1β to WT peritoneal macrophages damaged the epithelial barrier of C. rodentium-infected polarized CMT-93 cells. Treatment of Nlrp3-/- mice with IL-1β seems to confer protection against C. rodentium infection by reducing colonization, protecting epithelial integrity, and improving macrophage activity, while extraneous IL-1β appeared to be detrimental to WT mice.

Conclusions: These findings highlight the importance of balanced cytokine responses as IL-1β improved bacterial clearance in Nlrp3-/- mice but increased tissue damage when given to WT mice.

PMID: 24312491

 

SUPPLEMENT

This study was performed to better characterize the role of NLRP3 protein in early stages of Citrobacter rodentium infection and to determine if administration of IL-1β to Nlrp3-/- mice would overcome the lack of NLRP3 inflammasome. Our findings indicate that compensation of IL-1β in mice lacking the NLRP3 inflammasome may promote the clearance of C. rodentium. This clearance can be attributed to an influx of macrophages in the early stages of infection. Conversely, and unexpectedly, the overcompensation of IL-1β is detrimental in wildtype mice.

Described in more details, we found that treatments with IL-1β lowered C. rodentium colonization in the colon and protected the epithelial integrity in Nlrp3-/- mice, but damaged the epithelial barrier in WT mice, suggesting that a balanced IL-1β response is required for effective barrier function. This trend was consistent with our findings in histology showing higher severity scores in IL-1β-treated WT mice relative to treated Nlrp3-/- mice.

The exacerbation of disease in IL-1β-treated WT mice was interesting as it showed that the overcompensation of IL-1β was injurious. These data draw parallel lines with mutations in the NLRP3 gene and the implications in multiple autoinflammatory diseases including Crohn disease, displaying the fine line between homeostasis and pathogenesis [1,2]. Finally, we showed that the deletion of the NLRP3 inflammasome restricted bacterial killing, leading to increases in bacterial loads in the lamina propria and translocation into the mucosa. IL-1β treatments increased infiltration of macrophages and reduced bacterial infiltration.

To elucidate why IL-1β treatment of WT mice made them more susceptible to epithelial injury, murine epithelial cells where inoculated with C. rodentium, with addition of macrophages isolated from mice and IL-1β. The combination of all three factors damaged the epithelial barrier, representing the detrimental potential of macrophages, especially in the presence of excessive IL-1β.

Taken together, these findings indicate that a delicate IL-1β cytokine balance is required to promote effective clearance of C. rodentium. Moreover, overcompensation of IL-1β in this system seems to be detrimental by inducing colonic damage. This study further supports the importance of the NLRP3 inflammasome and macrophages in enteric infections and gut homeostasis as well as inflammatory diseases and offers potential innovative approaches for manipulating these pathways to control gut inflammation.

REFERENCES

1. Verma D, Sarndahl E, Andersson H, Eriksson P, Fredrikson M, et al. (2012) The Q705K polymorphism in NLRP3 is a gain-of-function alteration leading to excessive interleukin-1beta and IL-18 production. PLoS One 7: e34977.

2. Villani AC, Lemire M, Fortin G, Louis E, Silverberg MS, et al. (2009) Common variants in the NLRP3 region contribute to Crohn’s disease susceptibility. Nat Genet 41: 71-76.

Figure for Biomed frontiers feature of PLoS1 paperFigure 1. (A) IL-1β treatments reduce colonic colonization of C. rodentium in Nlrp3-/- mice; (B) IL-1β treatments reduce C. rodentium penetration in Nlrp3-/- mice but elevate dissemination in WT mice; (C) Colitis scoring revealed elevated severity of disease in IL-1β-treated WT mice; (D) IL-1β treatments promote macrophage infiltration; (E) Overcompensation of IL-1β damages the epithelial barrier.

 

Acknowledgements: We would like to acknowledge Deenaz Zaidi, Richard Chan, Harsh Thaker, and Dr. Andre Buret (University of Calgary).

Copyright notice: The abstract and figures were reproduced/modified under the Creative Commons guidelines from PLoS One. This article has been published in PLoS One: Misagh Alipour et al., A Balanced IL-1β Activity is Required for Host Response to Citrobacter rodentium Infection. PLoS One. 2013 Dec 2;8(12):e80656.

Multiselect Ultimate Query Plugin by InoPlugs Web Design Vienna | Webdesign Wien and Juwelier SchönmannMultiselect Ultimate Query Plugin by InoPlugs Web Design Vienna | Webdesign Wien and Juwelier Schönmann