Related Experiment Video

Updated: Aug 15, 2026

Tractable Mammalian Cell Infections with Protozoan-primed Bacteria
13:54

Tractable Mammalian Cell Infections with Protozoan-primed Bacteria

Published on: April 2, 2013

Signal transduction during Legionella pneumophila entry into human monocytes

P Y Coxon1, J T Summersgill, J A Ramirez

  • 1Department of Microbiology and Immunology, University of Louisville, Louisville, Kentucky 40292, USA. pycoxo01@ulkyvm.louisville.edu

Infection and Immunity
|May 29, 1998
PubMed

Insights

Legionella pneumophila entry into monocytes triggers actin polymerization via tyrosine kinase (TK) and protein kinase C (PKC) signaling. This tyrosine phosphorylation is a general phagocytosis mechanism, not specific to L. pneumophila virulence.

Area of Science:

  • Immunology
  • Cell Biology
  • Microbiology

Background:

  • Legionella pneumophila causes Legionnaires' disease by replicating within human monocytes and macrophages.
  • Bacterial uptake by these cells is primarily mediated by complement receptor 3 (CR3)-dependent phagocytosis.
  • The molecular mechanisms, particularly the roles of actin polymerization and intracellular signaling, governing this process require further elucidation.

Purpose of the Study:

  • To investigate the involvement of actin polymerization and specific phosphorylation events in L. pneumophila uptake by monocytes.
  • To identify the key signaling kinases activated during bacterial internalization.
  • To determine if the observed phosphorylation patterns are specific to L. pneumophila or part of a general phagocytic pathway.

Main Methods:

  • Uptake inhibition assays were employed to study bacterial internalization.
  • Confocal microscopy was utilized to visualize cellular responses at the site of bacterial entry.
  • Western blotting and kinase inhibitors (genistein, tyrphostin, staurosporine) were used to analyze protein phosphorylation and identify involved kinases.

Main Results:

  • L. pneumophila entry induced actin polymerization and activated tyrosine kinase (TK) and protein kinase C (PKC) signaling.
  • Six major cellular proteins were identified as TK phosphorylated upon bacterial entry, with three associating with the cytoskeleton.
  • Similar tyrosine phosphorylation patterns were observed during CR3-mediated uptake of non-pathogenic bacteria (E. coli) and yeast (zymosan), suggesting a conserved mechanism.

Conclusions:

  • Phagocytosis of L. pneumophila by monocytes involves TK and PKC signaling pathways that activate actin polymerization.
  • The tyrosine phosphorylation observed during L. pneumophila uptake is a general host cell response to CR3-mediated phagocytosis, not a specific virulence factor.
  • These findings contribute to understanding the early host-pathogen interactions in Legionnaires' disease and innate immune cell responses.

More Related Videos

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection12:30

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection

Published on: November 22, 2013

Legionella pneumophila Outer Membrane Vesicles: Isolation and Analysis of Their Pro-inflammatory Potential on Macrophages08:34

Legionella pneumophila Outer Membrane Vesicles: Isolation and Analysis of Their Pro-inflammatory Potential on Macrophages

Published on: February 22, 2017

Related Concept Videos

Bacterial Signaling01:30

Bacterial Signaling

Bacterial signaling can occur within bacteria (intracellular) or between bacteria (intercellular). At times, a group of bacteria behaves like a community. To achieve this, they engage in quorum sensing, the perception of higher cell density that causes changes in gene expression. Quorum sensing involves both extracellular and intracellular signaling. The signaling cascade starts with a molecule called an autoinducer (AI). Individual bacteria produce AIs that move out of the bacterial cell...
Gene Regulation in Microbial Communities: Quorum Sensing01:28

Gene Regulation in Microbial Communities: Quorum Sensing

Quorum sensing is a mechanism of bacterial communication that enables coordinated gene expression in response to changes in population density. This facilitates collective behaviors that enhance survival, resource acquisition, and ecological adaptation. This process relies on small signaling molecules called autoinducers that accumulate as bacterial populations grow. When a critical threshold concentration of autoinducers is reached, bacterial cells collectively modify gene expression,...
Colonisation of Pathogens01:25

Colonisation of Pathogens

Pathogen colonization of host tissues is a critical step in the development of infectious diseases. Various pathogenic microorganisms, including bacteria, fungi, viruses, and protozoa, have evolved complex strategies to attach to, invade, and persist within host environments. These mechanisms enable pathogens to establish infections, evade immune responses, and resist antimicrobial treatments.Attachment to Host CellsIn bacteria, colonization typically begins with adherence to host epithelial...