Toll-like receptor 2- and MyD88-dependent phosphatidylinositol 3-kinase and Rac1 activation facilitates the phagocytosis of Listeria monocytogenes by murine macrophages

Infect Immun. 2010 Jun;78(6):2857-67. doi: 10.1128/IAI.01138-09. Epub 2010 Apr 5.


Toll-like receptors (TLRs) play a key role in the innate immune response by sensing bacterial ligands. The mechanisms involved in the TLR-mediated cytokine response are well established; however, the possible contribution of TLR-dependent recognition of bacteria to macrophage phagocytosis remains unclear. Listeria monocytogenes is an intracellular, parasitic, Gram-positive bacterium recognized mainly by TLR2. In this study, we investigated whether TLR2-dependent signaling is involved in the phagocytosis of L. monocytogenes by macrophages. We found no difference in the number of L. monocytogenes cells associating with wild-type (WT) and TLR2(-/-) macrophages 1 h after infection. However, the number of L. monocytogenes cells phagocytosed in TLR2(-/-) and MyD88(-/-) macrophages was significantly lower than that of WT macrophages. In addition, lipopolysaccharide (LPS) treatment restored impaired phagocytic activity of TLR2(-/-) macrophages but did not enhance the activity of MyD88(-/-) macrophages. The efficiency of phagocytosis was suppressed by inhibitors of phosphatidylinositol 3-kinase (PI3K) and the small Rho GTPases but not by cycloheximide. Moreover, functional activation of PI3K and Rac1 was impaired in TLR2(-/-) and MyD88(-/-) macrophages. In an in vivo infection model, we found significantly lower numbers of L. monocytogenes cells phagocytosed in peritoneal macrophages of TLR2(-/-) and MyD88(-/-) mice after intraperitoneal infection. Moreover, a lower number of bacteria were detected in the spleens of TLR2(-/-) mice 1 day after intravenous infection than in WT mice. These results clearly indicated that TLR2-MyD88-dependent signaling enhances the basal level of phagocytosis of L. monocytogenes by macrophages through activation of PI3K and Rac1, not by synthesis of proinflammatory cytokines or expression of phagocytic receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Female
  • Listeria monocytogenes / immunology*
  • Listeriosis / immunology
  • Macrophages / immunology*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Myeloid Differentiation Factor 88 / deficiency
  • Myeloid Differentiation Factor 88 / immunology*
  • Neuropeptides / antagonists & inhibitors
  • Neuropeptides / metabolism*
  • Peritoneal Cavity / microbiology
  • Phagocytosis*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Spleen / microbiology
  • Toll-Like Receptor 2 / deficiency
  • Toll-Like Receptor 2 / immunology*
  • rac GTP-Binding Proteins / antagonists & inhibitors
  • rac GTP-Binding Proteins / metabolism*
  • rac1 GTP-Binding Protein


  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Neuropeptides
  • Phosphoinositide-3 Kinase Inhibitors
  • Rac1 protein, mouse
  • Tlr2 protein, mouse
  • Toll-Like Receptor 2
  • rac GTP-Binding Proteins
  • rac1 GTP-Binding Protein