Related Experiment Video
Updated: Jan 30, 2026
Harvesting Murine Alveolar Macrophages and Evaluating Cellular Activation Induced by Polyanhydride Nanoparticles
Published on: June 8, 2012
Alveolar Macrophage Apoptosis-associated Bacterial Killing Helps Prevent Murine Pneumonia
Julie A Preston1,2, Martin A Bewley1,2, Helen M Marriott1,2
11 The Florey Institute for Host-Pathogen Interactions and.
Abstract:
Rationale: Antimicrobial resistance challenges therapy of pneumonia. Enhancing macrophage microbicidal responses would combat this problem but is limited by our understanding of how alveolar macrophages (AMs) kill bacteria. Objectives: To define the role and mechanism of AM apoptosis-associated bacterial killing in the lung. Methods: We generated a unique CD68.hMcl-1 transgenic mouse with macrophage-specific overexpression of the human antiapoptotic Mcl-1 protein, a factor upregulated in AMs from patients at increased risk of community-acquired pneumonia, to address the requirement for apoptosis-associated killing. Measurements and Main Results: Wild-type and transgenic macrophages demonstrated comparable ingestion and initial phagolysosomal killing of bacteria. Continued ingestion (for ≥12 h) overwhelmed initial killing, and a second, late-phase microbicidal response killed viable bacteria in wild-type macrophages, but this response was blunted in CD68.hMcl-1 transgenic macrophages. The late phase of bacterial killing required both caspase-induced generation of mitochondrial reactive oxygen species and nitric oxide, the peak generation of which coincided with the late phase of killing. The CD68.hMcl-1 transgene prevented mitochondrial reactive oxygen species but not nitric oxide generation. Apoptosis-associated killing enhanced pulmonary clearance of Streptococcus pneumoniae and Haemophilus influenzae in wild-type mice but not CD68.hMcl-1 transgenic mice. Bacterial clearance was enhanced in vivo in CD68.hMcl-1 transgenic mice by reconstitution of apoptosis with BH3 mimetics or clodronate-encapsulated liposomes. Apoptosis-associated killing was not activated during Staphylococcus aureus lung infection. Conclusions: Mcl-1 upregulation prevents macrophage apoptosis-associated killing and establishes that apoptosis-associated killing is required to allow AMs to clear ingested bacteria. Engagement of macrophage apoptosis should be investigated as a novel, host-based antimicrobial strategy.
Insights
Macrophage apoptosis aids bacterial clearance in pneumonia. Upregulating Mcl-1 protein blocks this crucial cell death pathway, hindering bacterial killing and suggesting apoptosis as a novel antimicrobial strategy.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Antimicrobial resistance necessitates novel therapeutic strategies for pneumonia.
- Alveolar macrophages (AMs) play a key role in lung immunity, but their bacterial killing mechanisms require further elucidation.
- Understanding how AMs eliminate bacteria is crucial for developing host-directed antimicrobial approaches.
Purpose of the Study:
- To investigate the role and mechanism of apoptosis-associated bacterial killing by AMs in the lung.
- To determine if Mcl-1, an antiapoptotic protein, influences AM-mediated bacterial clearance.
Main Methods:
- Generated CD68.hMcl-1 transgenic mice with macrophage-specific overexpression of human Mcl-1.
- Assessed bacterial ingestion, phagolysosomal killing, and late-phase microbicidal responses in wild-type and transgenic macrophages.
- Investigated the role of mitochondrial reactive oxygen species and nitric oxide in apoptosis-associated killing.
- Evaluated bacterial clearance of *Streptococcus pneumoniae* and *Haemophilus influenzae* in vivo.
- Restored apoptosis-associated killing in transgenic mice using BH3 mimetics and clodronate-encapsulated liposomes.
Main Results:
- While initial bacterial killing was comparable, wild-type macrophages exhibited a late-phase microbicidal response involving apoptosis, which was blunted in Mcl-1 overexpressing macrophages.
- This late-phase killing required caspase-induced mitochondrial reactive oxygen species and nitric oxide generation.
- Mcl-1 overexpression impaired the clearance of *S. pneumoniae* and *H. influenzae* in vivo, but this could be restored by inducing apoptosis.
- Apoptosis-associated killing was not observed during *Staphylococcus aureus* lung infection.
Conclusions:
- Mcl-1 upregulation inhibits macrophage apoptosis-associated bacterial killing, highlighting its necessity for effective clearance of certain ingested bacteria.
- Targeting macrophage apoptosis presents a promising, host-based antimicrobial strategy against pneumonia-causing pathogens like *S. pneumoniae* and *H. influenzae*.
Related Concept Videos
01:30Pneumonia V: Nursing management and Prevention
The nurse must practice strict medical asepsis and adhere to infection control guidelines to minimize healthcare-associated infections.
Enhance airway patency
Position the patient correctly to facilitate drainage of the affected lung segments. Manual or mechanical percussion and vibration can also be employed....
01:30Apoptosis
01:26Alveoli and Alveolar Ducts
01:30Pneumonia I: Introduction
Risk Factors
Various factors influence the likelihood of developing pneumonia. Age plays a crucial role, with infants, children under two, and individuals over 65 at increased risk due to their...
01:29Pneumonia II: Pathophysiology
02:59Cancer Prevention
Some...