CYTOLOGIC EVALUATION OF BRONCHOALVEOLAR LAVAGE FLUID OBTAINED FROM STANDARD-BRED RACEHORSES WITH INFLAMMATORY AIRWAY DISEASE

Cytologic examination of bronchoalveolar lavage fluid (BALF), includin g phenotypic analysis of lymphocytes, was performed on 32 Standardbred s with poor race performance and endoscopic examination findings chara cteristic of inflammatory airway disease (IAD). Nucleated cell counts in BALF from IAD-affected horses were higher than those in control hor ses; the cytologic profile of BALF in affected horses included mixed i nflammation, characterized by mild neutrophilia, lymphocytosis, and mo nocytosis. Eosinophil and mast cell counts were not higher in the IAD- affected group, compared with those in the control group; however, 4 I AD-affected horses had marked eosinophilia (24.7 +/- 4.8% SEM) in BALF . Phenotypic analysis of lymphocytes in BALF obtained from IAD-affecte d horses revealed a low proportion of CD4-positive cells and B cells, compared with those in the control group; these finding; may have been representative of a greater proportion of non-B, non-T cells (null ce lls) in horses with IAD. The cytologic profile of BALF obtained from h orses with IAD differed from that in horses affected with chronic obst ructive pulmonary disease, suggesting that the pathogenesis of inflamm ation in horses with IAD may differ from that of chronic obstructive p ulmonary disease.