Response of Peripheral Blood Lymphocytes from RAO-affected Horses to b2-Agonist Stimulation

Recurrent airway obstruction (RAO) affects middle-age horses, inducing bronchoconstriction and airway inflammation. β2-agonists like salbutamol are used as treatment, promoting airway smooth muscle (ASM) relaxation and bronchodilation. In addition to ASM, inflammatory cells express the β2-adrenoreceptors (β2-AR). In other species, β2-agonists promote peripheral blood lymphocyte (PBL) cytokine expression towards a pro-inflammatory phenotype. RAO horses are a good model for evaluating chronic changes in human asthma. However, little is known about the effect of β2-agonist stimulation on equine PBL inflammatory response. The aims of this study were to develop an indirect method to evaluate the response of equine PBLs to β2-agonist stimulation, and to compare it between cells from RAO and non-affected horses. Isolated PBLs were activated with ConA and stimulated with salbutamol. Response to agonist binding was indirectly determined using flow cytometric methodology and verified by Western blot. Activated PBLs from RAO horses demonstrated a significant response to β2-agonist binding whereas cells from non-affected horses did not. Response of PBLs from RAO horses was attenuated when pre-treated with a β2-antagonist but unaffected following pre-treatment with a β1-antagonist, indicating that the response of PBLs from these horses to salbutamol binding was mainly through the β2-AR. Preliminary investigation of bronchoalveolar lavage (BAL) lymphocytes from RAO horses demonstrated that they also responded to β2-agonist binding, while cells from non-affected horses did not. These findings represent a novel tool for further investigation of the role of β2-agonist binding in diseases like asthma and RAO, and support the use of this model for future studies.