Inhaled endotoxin and organic dust particulates have synergistic proinflammatory effects in equine heaves (organic dust-induced asthma).
Abstract: Equine heaves is a naturally occurring organic dust-induced asthma characterized by airway neutrophilia, mucus hypersecretion and obstructive lung dysfunction. However, the relative role of different dust components in disease severity remains unclear. Objective: This study investigated the relative contribution of inhaled endotoxin and organic dust particulates (mainly mould spores) in inducing heaves in heaves-susceptible horses. Methods: Control and heaves-susceptible horses received inhalation challenges with hay dust suspension (HDS) before and after lipopolysaccharide (LPS) depletion. Heaves-susceptible horses also received inhalation challenge with HDS particulates with and without the addition of LPS and were housed in two separate dusty environments during which mould and endotoxin exposure was measured. The airway inflammatory and functional response to each challenge was measured. Results: Depletion of endotoxin from HDS attenuated the airway neutrophilia and abrogated the airway dysfunction induced in heaves horses by inhaled HDS. The airway response was re-established by adding back LPS to the depleted HDS, confirming that the attenuation in airway response was due specifically to endotoxin depletion. Interestingly, the magnitude of alteration in airway response following endotoxin depletion and add-back was greater than that which could be attributed solely to endotoxin per se, indicating that the LPS activity was enhanced by the other dust components. Consistent with this possibility, washed particulates harvested from HDS enhanced the airway response to inhaled LPS in heaves horses. Heaves horses given two different hay/straw challenges had a significantly different severity of airway inflammation and dysfunction, despite airborne dust and endotoxin concentrations in the horses' breathing zones being similar. Conclusions: Although inhaled endotoxin appears not to be the only determinant of disease severity in heaves, it does contribute significantly to the induction of airway inflammation and dysfunction. This contribution is largely via the synergistic action of inhaled endotoxin and organic dust particulates, although other soluble dust components also contribute to a lesser degree.
Publication Date: 2003-05-20 PubMed ID: 12752598DOI: 10.1046/j.1365-2222.2003.01640.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study investigates the role of inhaled endotoxin and organic dust particulates, mainly mold spores, in causing a type of asthma in horses known as ‘heaves.’ The researchers found that while inhaled endotoxin contributes significantly to airway inflammation and dysfunction, it is not the only determinant of the disease severity.
Research Objective and Methods
- The experiment aimed to understand the role that different components found in dust, specifically endotoxin and organic dust particulates, play in the severity of equine heaves, a type of asthma in horses characterized by airway inflammation, excess mucus, and impaired lung function.
- The study involved control and heaves-susceptible horses receiving inhalation challenges with a hay dust suspension (HDS) before and after lipopolysaccharide (LPS) depletion. LPS is a type of endotoxin found in dust.
- Heaves-susceptible horses were also exposed to HDS particulates with and without LPS addition, and were kept in two separate dusty environments, allowing the researchers to monitor mold and endotoxin exposure.
- The airway response of the horses was measured after each challenge.
Research Findings
- The study found that depletion of endotoxin from HDS reduced the severity of airway inflammation in affected horses, both in terms of inflammation and overall lung function. When LPS was reintroduced to the depleted HDS, the detrimental airway response was reinstated, pointing to the specific role of endotoxin in eliciting the symptoms of heaves.
- Interestingly, the alteration in the airway response following the depletion and addition of LPS was more pronounced than what could be attributed solely to the endotoxin, suggesting that the chemical reaction of LPS is enhanced by other dust components.
- This theory was further validated by the fact that washed particulates from HDS intensified the airway response to inhaled endotoxin in heaves horses.
- Horses exposed to two different types of hay/straw treatments showed variations in the severity of airway inflammation and dysfunction, despite similar concentrations of airborne dust and endotoxin in their breathing environments.
Conclusions
- These findings verify that while inhaled endotoxin contributes substantially to the induction of airway inflammation and dysfunction in horses suffering from heaves, it is not the sole contributor to disease severity. Other components of organic dust also play an influential role.
- The study revealed a synergistic effect between inhaled endotoxin and organic dust particulates, suggesting that these components enhance either’s activity, leading to an exacerbation of the condition. Still, other soluble dust components may contribute to a lesser extent as well.
Cite This Article
APA
Pirie RS, Collie DD, Dixon PM, McGorum BC.
(2003).
Inhaled endotoxin and organic dust particulates have synergistic proinflammatory effects in equine heaves (organic dust-induced asthma).
Clin Exp Allergy, 33(5), 676-683.
https://doi.org/10.1046/j.1365-2222.2003.01640.x Publication
Researcher Affiliations
- Wellcome Trust Centre for Research in Comparative Respiratory Medicine, Easter Bush Veterinary Centre, Roslin, Midlothian, UK. scottp@staffmail.ed.ac.uk
MeSH Terms
- Animals
- Asthma / etiology
- Asthma / pathology
- Asthma / veterinary
- Bronchoalveolar Lavage Fluid / cytology
- Cell Count
- Dust / immunology
- Edible Grain / immunology
- Endotoxins / toxicity
- Female
- Horse Diseases / etiology
- Horse Diseases / pathology
- Horses
- Inhalation Exposure
- Lipopolysaccharides / toxicity
- Spores, Fungal / immunology
Citations
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