Bacterial Outer Membrane Vesicles Mediate Cytosolic Localization of LPS and Caspase-11 Activation

Cell. 2016 May 19;165(5):1106-1119. doi: 10.1016/j.cell.2016.04.015. Epub 2016 May 5.


Sensing of lipopolysaccharide (LPS) in the cytosol triggers caspase-11 activation and is central to host defense against Gram-negative bacterial infections and to the pathogenesis of sepsis. Most Gram-negative bacteria that activate caspase-11, however, are not cytosolic, and the mechanism by which LPS from these bacteria gains access to caspase-11 in the cytosol remains elusive. Here, we identify outer membrane vesicles (OMVs) produced by Gram-negative bacteria as a vehicle that delivers LPS into the cytosol triggering caspase-11-dependent effector responses in vitro and in vivo. OMVs are internalized via endocytosis, and LPS is released into the cytosol from early endosomes. The use of hypovesiculating bacterial mutants, compromised in their ability to generate OMVs, reveals the importance of OMVs in mediating the cytosolic localization of LPS. Collectively, these findings demonstrate a critical role for OMVs in enabling the cytosolic entry of LPS and, consequently, caspase-11 activation during Gram-negative bacterial infections.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Outer Membrane Proteins / metabolism
  • Cytosol / metabolism
  • Enzyme Activation
  • Gram-Negative Bacteria / chemistry
  • Gram-Negative Bacteria / cytology*
  • Gram-Negative Bacterial Infections / immunology*
  • Gram-Negative Bacterial Infections / microbiology*
  • Immunity, Innate
  • Inflammation / immunology
  • Inflammation / microbiology
  • Interleukin-1 / immunology
  • Lipopolysaccharides / metabolism*
  • Mice


  • Bacterial Outer Membrane Proteins
  • Interleukin-1
  • Lipopolysaccharides