Abstract
Severe equine asthma (SEA) is a common, debilitating lower airway inflammatory disorder of older horses. Alveolar macrophages (AMs) survey inhaled particulates from barn sources causing them to switch from an anti-inflammatory to a proinflammatory phenotype, resulting in neutrophil recruitment to the lung. This proinflammatory switch may contribute to the development and prolongation of SEA. Validated antibodies to identify the cells involved in the pathogenesis of SEA are lacking. In this study, monoclonal antibodies against CD90, CD163, and CD206 were tested for reactivity with equine leukocytes by immunocytochemistry and flow cytometry. A multi-color flow cytometric assay was developed to identify leukocytes in equine bronchoalveolar lavage fluid (BALF). Four control and 4 SEA-susceptible horses had BALF collected before and after a 48-hour moldy hay challenge. Antibodies against CD90 uniquely labeled equine neutrophils, and antibodies against CD163 and CD206 identified equine macrophages. Postchallenge AM surface expression of CD163 increased in both groups of horses, but the increase was statistically significant in only the SEA-susceptible group (P = .02). The surface expression of CD206 on AMs increased significantly in the SEA-susceptible group (P = .03) but was unchanged in the control group (P = .5). Increased expression of CD163 and CD206 during exacerbation of SEA suggested an association between AM phenotype and lung inflammation. However, functions of AMs in the pathogenesis of SEA remain to be elucidated.
Highlights
Severe equine asthma (SEA) is a common, debilitating lower airway inflammatory disorder of older horses
Immunocytochemistry was performed on charged slide cytocentrifuge (41 Â g for 6 minutes) preparations of bronchoalveolar lavage fluid (BALF) leukocytes from a horse in exacerbation of SEA
Neutrophils were identified by their segmented nucleus
Summary
Severe equine asthma (SEA) is a common, debilitating lower airway inflammatory disorder of older horses. Persistent exacerbation results in long-term airway inflammation leading to airway remodeling and ultrastructural changes in the bronchoalveolar tree.[10,15,26,27,30] clinical signs are improved by reducing barn- and feed-related dusts, and drug therapy, the disease is progressive and periods of exacerbation result in reduced quality of life due to severe respiratory impairment.[3,38,42] In experimental models, SEA exacerbation can be induced in susceptible horses through exposure to dusty hay or a mixture organic and inorganic particulates and lipopolysaccharide, which represent the asthma triggering components of hay dust.[5,26] Because the inflammation associated with SEA is diffuse, a single bronchoalveolar lavage fluid (BALF) sample is representative of the process affecting the distal airways.[33] Cytologically, SEA is defined by counting >25% neutrophils, and variable proportions of lymphocytes and alveolar macrophages (AMs) in the BALF differential cell count.[12]. Novus Biologicals, Oakville, Ontario, Canada Washington State University, Pullman, WA Thermo Fisher Scientific, Mississauga, Ontario, Canada BioLegend, San Diego, CA Beckman Coulter, Mississauga, Ontario, Canada Bio-Rad, Mississauga, Ontario, Canada Bio-Rad, Mississauga, Ontario, Canada
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