Bronchial brush cytology, endobronchial biopsy, and SALSA immunohistochemistry in severe equine asthma.
Authors: Lee Gary K C, Beeler-Marfisi Janet, Viel Laurent, Piché Érica, Kang Heng, Sears William, Bienzle Dorothee
Journal: Veterinary pathology
Summary
Severe equine asthma (SEA) is characterised by persistent neutrophilic airway inflammation, traditionally diagnosed via bronchoalveolar lavage (BAL) cytology, but this study investigated whether bronchial brush cytology and tissue biomarkers might offer equally useful diagnostic alternatives. Researchers collected BAL fluid, bronchial brushings, and endobronchial biopsies from six asthmatic and six non-asthmatic horses before and after inhaled allergen challenge, analysing neutrophil proportions, histopathological changes, and immunohistochemical expression of salivary scavenger and agglutinin (SALSA)—a protein with anti-inflammatory properties that is typically downregulated in SEA. Following challenge, asthmatic horses exhibited markedly elevated neutrophil percentages in both BAL fluid (80.9% versus 3.6%) and bronchial brush cytology (39.5% versus 0.2%), demonstrating that brush cytology reliably reflects intraluminal airway inflammation without requiring lavage procedures. Conversely, bronchial biopsy findings and SALSA immunolabelling showed minimal differences between groups, suggesting that acute challenge produces primarily luminal rather than tissue-level changes; serum amyloid A levels rose in asthmatic horses, indicating systemic inflammation, but SALSA expression did not change significantly. For practitioners, these findings support brush cytology as a practical and potentially less invasive diagnostic tool for confirming SEA, whilst tissue biomarkers and histopathology appear less useful for acute disease detection, though their value in chronic management warrants further investigation.
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Practical Takeaways
- •Bronchial brush cytology offers a practical alternative to BAL for diagnosing SEA when BAL is not feasible, with clear differentiation between healthy and asthmatic horses based on neutrophil percentages.
- •SALSA immunostaining of bronchial biopsies did not prove useful for SEA diagnosis in this study, so practitioners should continue relying on BAL or brush cytology rather than expecting tissue biomarkers to confirm disease.
- •Systemic inflammation markers (serum amyloid A) increase in SEA but do not correlate with local bronchial tissue changes, suggesting SEA is primarily a disease of intraluminal airway inflammation rather than structural tissue damage.
Key Findings
- •Bronchial brush cytology showed significantly higher neutrophil proportions in asthmatic horses (39.5%) versus non-asthmatic horses (0.2%) after inhaled challenge, suggesting brush cytology is a viable alternative to BAL for assessing lower airway inflammation.
- •BAL fluid neutrophil proportions were markedly elevated in asthmatic horses (80.9%) compared to controls (3.6%) after challenge, confirming persistent neutrophilic inflammation in SEA.
- •SALSA immunohistochemical labeling in bronchial tissue did not significantly change between asthmatic and non-asthmatic horses despite systemic inflammation markers (SAA) being elevated, limiting its utility as a tissue biomarker for SEA diagnosis.
- •Endobronchial histopathologic findings were similar between asthmatic and non-asthmatic horses following inhaled challenge, indicating acute challenge produces minimal structural bronchial tissue changes.