Macrophages lift off surface-bound bacteria using a filopodium-lamellipodium hook-and-shovel mechanism

Sci Rep. 2013 Oct 7:3:2884. doi: 10.1038/srep02884.

Abstract

To clear pathogens from host tissues or biomaterial surfaces, phagocytes have to break the adhesive bacteria-substrate interactions. Here we analysed the mechanobiological process that enables macrophages to lift-off and phagocytose surface-bound Escherichia coli (E. coli). In this opsonin-independent process, macrophage filopodia hold on to the E. coli fimbriae long enough to induce a local protrusion of a lamellipodium. Specific contacts between the macrophage and E. coli are formed via the glycoprotein CD48 on filopodia and the adhesin FimH on type 1 fimbriae (hook). We show that bacterial detachment from surfaces occurrs after a lamellipodium has protruded underneath the bacterium (shovel), thereby breaking the multiple bacterium-surface interactions. After lift-off, the bacterium is engulfed by a phagocytic cup. Force activated catch bonds enable the long-term survival of the filopodium-fimbrium interactions while soluble mannose inhibitors and CD48 antibodies suppress the contact formation and thereby inhibit subsequent E. coli phagocytosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adhesins, Bacterial / metabolism
  • Adhesins, Escherichia coli / metabolism
  • Antigens, CD / metabolism
  • Bacterial Adhesion / immunology*
  • CD48 Antigen
  • Cell Line
  • Cell Membrane / immunology
  • Cell Membrane / metabolism
  • Escherichia coli / physiology
  • Escherichia coli / ultrastructure
  • Fimbriae Proteins / metabolism
  • Humans
  • Macrophages / microbiology*
  • Macrophages / physiology*
  • Macrophages / ultrastructure
  • Models, Biological
  • Phagocytosis / immunology
  • Pseudopodia / physiology*
  • Shear Strength

Substances

  • Adhesins, Bacterial
  • Adhesins, Escherichia coli
  • Antigens, CD
  • CD48 Antigen
  • CD48 protein, human
  • fimH protein, E coli
  • Fimbriae Proteins