Alveolar macrophage phenotypes in severe equine asthma.
Authors: Wilson M E, McCandless E E, Olszewski M A, Robinson N Edward
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Alveolar Macrophage Phenotypes in Severe Equine Asthma Alveolar macrophages are central to airway immune responses, yet their functional characteristics in severe equine asthma (SEA) remain poorly defined. Wilson and colleagues investigated whether naturally hay/straw challenged horses and controls develop distinct macrophage phenotypes by first establishing M1 and M2 polarisation patterns in vitro using equine interferon-gamma/lipopolysaccharide and equine interleukin-4 stimulation respectively, then examining gene expression in horses at pasture and following natural challenge (NC). Control horses mounted a dynamic response to NC, displaying elevated interleukin-10 (IL-10) and increased CD206 expression only after challenge; in contrast, horses with SEA showed consistently elevated IL-10 expression both at pasture and post-challenge, alongside heightened IL-8 and IL-10 responses to pathogen-associated molecular patterns at baseline. The fundamental finding—that macrophages in SEA maintain a constitutively shifted phenotype characterised by elevated IL-10 rather than responding adaptively to environmental triggers—suggests that diseased horses have lost critical immunoregulatory flexibility. This altered macrophage polarisation may perpetuate airway inflammation through impaired dynamic switching between pro- and anti-inflammatory states, with implications for how we approach therapeutic interventions: targeting macrophage phenotype plasticity rather than simply suppressing inflammation could offer a more physiologically aligned treatment strategy for SEA.
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Practical Takeaways
- •Horses with severe asthma have macrophage dysfunction characterized by persistent elevation of anti-inflammatory IL-10, which may explain their inability to clear dust antigens effectively—managing environmental dust exposure becomes even more critical for these horses
- •The loss of dynamic macrophage responsiveness in SEA suggests that affected horses cannot adapt their immune response to changing environmental conditions, supporting year-round stable management strategies and hay steaming/soaking
- •Understanding that SEA involves fundamental macrophage polarization abnormalities rather than just acute inflammatory responses may inform development of immunomodulatory treatments beyond standard corticosteroid or bronchodilator protocols
Key Findings
- •M1-polarized alveolar macrophages in control horses expressed elevated pro-inflammatory cytokines (TNF-α, IL-8, IL-12p40) and CD80, while M2-polarization increased CD206 expression
- •Horses with SEA demonstrated consistently elevated IL-10 expression in alveolar macrophages both at pasture and after natural hay/straw challenge, indicating a fundamental shift toward a non-canonical phenotype
- •Natural challenge selectively increased IL-10 expression in control horses to match SEA levels, eliminating baseline differences in PAMP-stimulated IL-8 and IL-10 responses between groups
- •Alveolar macrophages in horses with SEA appear to have lost the ability to dynamically shift phenotypes in response to environmental cues compared to control horses