Abstract

Host recognition of microbial components is essential in mediating an effective immune response. Cytosolic bacteria must secure entry into the host cytoplasm to facilitate replication and, in doing so, liberate microbial ligands that activate cytosolic innate immune sensors and the inflammasome. Here, we identified a multicomponent enterotoxin, haemolysin BL (HBL), that engages activation of the inflammasome. This toxin is highly conserved among the human pathogen Bacillus cereus. The three subunits of HBL bind to the cell membrane in a linear order, forming a lytic pore and inducing activation of the NLRP3 inflammasome, secretion of interleukin-1β and interleukin-18, and pyroptosis. Mechanistically, the HBL-induced pore results in the efflux of potassium and triggers the activation of the NLRP3 inflammasome. Furthermore, HBL-producing B. cereus induces rapid inflammasome-mediated mortality. Pharmacological inhibition of the NLRP3 inflammasome using MCC950 prevents B. cereus-induced lethality. Overall, our results reveal that cytosolic sensing of a toxin is central to the innate immune recognition of infection. Therapeutic modulation of this pathway enhances host protection against deadly bacterial infections.

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Acknowledgements

The authors would like to thank V. M. Dixit (Genentech, USA), K. Schroder (Institute of Molecular Bioscience, Australia), P. Broz (University of Lausanne, Switzerland), J. Ng (Westmead Hospital, Australia), A. Rice (The Canberra Hospital, Australia) and J. Bates (Department of Health Queensland, Australia) for reagents. They also thank B. Quah (ANU, Australia), C. Gillespie (ANU, Australia), I. Sastalla (National Institutes of Health, USA), M. Rug (Centre for Advanced Microscopy, ANU, Australia), J. Lee (Centre for Advanced Microscopy, ANU, Australia), C. O’Brien (The Canberra Hospital, Australia) and D. Gordon (ANU, Australia) for assistance. A.M. is supported by a John Curtin School of Medical Research International Ph.D. scholarship. S.H.L. is supported, in part, by the Intramural Program of the National Institute of Allergy and Infectious Diseases, NIH, USA. N.O.K. is supported by a Career Development Fellowship from the Cancer Institute NSW (15/CDF/1-11). S.M.M. is supported by the Australian National University, The Gretel and Gordon Bootes Medical Research Foundation, and the National Health and Medical Research Council of Australia (under Project Grants APP1141504 and APP1146864) and the R.G. Menzies Early Career Fellowship (APP1091544).

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Affiliations

  1. Department of Immunology and Infectious Disease, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia

    • Anukriti Mathur
    • , Shouya Feng
    • , Jenni A. Hayward
    • , Chinh Ngo
    • , Daniel Fox
    • , Gaetan Burgio
    •  & Si Ming Man
  2. Lipotek Pty Ltd, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia

    • Ines I. Atmosukarto
    •  & Jason D. Price
  3. Department of Veterinary Sciences, Faculty of Veterinary Medicine, Ludwig-Maximilians-Universität München, Oberschleißheim, Germany

    • Kristina Schauer
    •  & Erwin Märtlbauer
  4. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia

    • Avril A. B. Robertson
  5. Commonwealth Scientific and Industrial Research Organisation (CSIRO) Agriculture and Food, Werribee, Victoria, Australia

    • Edward M. Fox
  6. Microbial Pathogenesis Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA

    • Stephen H. Leppla
  7. School of Medical Sciences, UNSW Sydney, Sydney, New South Wales, Australia

    • Nadeem O. Kaakoush

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Contributions

A.M. and S.M.M. conceptualized the study. A.M., S.F., J.A.H., C.N., D.F., I.I.A., J.D.P. and N.O.K. performed the experiments. A.M., S.F., J.A.H., C.N., D.F. and N.O.K. conducted the analyses, and A.M. and S.M.M. wrote the manuscript. S.M.M. acquired the funding, and I.I.A., J.D.P., K.S., E.M., A.A.B.R., G.B., E.M.F. and S.H.L. provided resources and intellectual input. S.M.M. provided overall supervision, and all authors reviewed the manuscript.

Competing interests

I.I.A. is Director of Lipotek, a niche biotech company with a focus on liposome technology. I.I.A. and J.D.P. are shareholders of Lipotek. A.A.B.R. is a named inventor on inflammasome inhibitor patents (WO2017140778 and WO2016131098). All other authors have no competing interests.

Corresponding author

Correspondence to Si Ming Man.

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https://doi.org/10.1038/s41564-018-0318-0