Related Experiment Videos
Role of the platelet-activating factor (PAF) receptor during pulmonary infection with gram negative bacteria
A C Soares1, V S Pinho, D G Souza
1Immunopharmacology Laboratory, Departamento de Bioquímica e Imunolgia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Abstract:
The lipid mediator PAF plays an important role in the phagocytosis of particles, including bacteria, and consequent production of pro-inflammatory cytokines, such as TNF-alpha and IL-8. Using a PAF receptor antagonist (UK-74,505) and PAF receptor knock-out mice, we have investigated the relevance of PAF for the inflammatory changes and lethality after pulmonary infection with the gram-negative bacteria Klebsiella pneumoniae in mice. At an inoculum of 3 x 10(6) bacteria, there was marked pulmonary (bronchoalveolar lavage and lung) neutrophilia that started early (2.5 h after infection) and peaked at 48 h. All animals were dead by day 4 of infection. The chemokine KC and the pro-inflammatory cytokine TNF-alpha increased rapidly and persisted for 48 h in the lungs. Pretreatment with UK-74,505 (30 mg kg(-1) per day, p.o.) had no significant effects on the number of infiltrating neutrophils in BAL fluid or lung tissue, as assessed by histology and measuring myeloperoxidase, or on the concentrations of KC. In contrast, concentrations of TNF-alpha and the number of bacteria inside neutrophils were significantly diminished. In order to support a role for the PAF during K. pneumoniae infection, experiments were also carried out in PAFR-deficient mice. In the latter animals, lethality occurred earlier than in wild-type controls. This was associated with greater number of bacteria in lung tissue and diminished percentage of neutrophils containing bacteria in their cytoplasm. Our results suggest that PAF, acting on its receptor, plays a protective role during infection with K. pneumoniae in mice.
Insights
Platelet-activating factor (PAF) surprisingly protects against Klebsiella pneumoniae lung infection. Blocking PAF exacerbates bacterial load and inflammation, indicating a crucial protective role for PAF signaling in host defense.
Area of Science:
- Immunology
- Microbiology
- Pulmonary Medicine
Background:
- Platelet-activating factor (PAF) is a lipid mediator involved in particle phagocytosis and pro-inflammatory cytokine production.
- Its role in bacterial lung infections, specifically Klebsiella pneumoniae, requires further elucidation.
Purpose of the Study:
- To investigate the role of PAF in inflammatory responses and lethality during Klebsiella pneumoniae pulmonary infection in mice.
- To assess the impact of PAF receptor antagonism and deficiency on infection outcomes.
Main Methods:
- Utilized a PAF receptor antagonist (UK-74,505) and PAF receptor knock-out (PAFR-deficient) mice.
- Administered Klebsiella pneumoniae via pulmonary infection.
- Assessed pulmonary neutrophilia, cytokine (TNF-alpha, IL-8, KC) and chemokine levels, bacterial load, and neutrophil phagocytosis via bronchoalveolar lavage (BAL), histology, and myeloperoxidase assays.
Main Results:
- PAF receptor antagonism did not affect neutrophil infiltration or KC levels but significantly reduced TNF-alpha and bacterial burden within neutrophils.
- PAFR-deficient mice exhibited earlier lethality, increased lung bacterial load, and reduced neutrophil bacterial phagocytosis compared to wild-type controls.
- PAF signaling was associated with reduced pro-inflammatory cytokine TNF-alpha and enhanced bacterial clearance by neutrophils.
Conclusions:
- PAF, acting through its receptor, plays a protective role in Klebsiella pneumoniae pulmonary infection in mice.
- Targeting PAF may not be beneficial and could potentially be detrimental in this specific bacterial lung infection model.