The aim was to study the effects of a -agonist (clen- buterol) on lipopolysaccharide (LPS)—induced cytokine expression of bronchoalveolar cells. Four horses with low-grade small airway diseases and four horses with re- current airway obstruction were challenged on three occasions with aerosols containing Salmonella LPS or a 0.9% saline solution. Before the first LPS challenge, horses were not treated. Before the second and third challenges, horses received intravenous clenbuterol (Ventipulmin), 0.8 μg/kg twice daily, for 3.5 days. A 2- week washout period was allowed between the chal- lenges. Bronchoalveolar lavage fluid (BALF) was ob- tained, and maximal intrapleural pressure ( P pl max) was measured 6 hours after each challenge. After cyto- logic examination was performed, the messenger RNA expression in the BALF cell pellet of the following cy- tokines was investigated by reverse-transcriptase poly- merase chain reaction: tumor necrosis factor- (TNF- ), interleukin (IL)-1 , IL-1 , IL-4, IL-6, IL-8 (CXCL8), IL-10, tissue growth factor- (TGF- ), and interferon- (IFN- ). Treatment with clenbuterol caused a decrease in maxi- mal intrapleural pressure toward more normal values in the recurrent airway obstruction group. IL-4 mRNA ex- pression could not be demonstrated. Only IFN- and IL- From the 1st Medical Clinic for Ungulates and Small Animals a and Institute of Medical Chemistry, b Veterinary University of Vienna, Veterinärplatz 1, Vienna, Austria. Supported by Boehringer-Ingelheim. Reprint requests: R. van den Hoven, DVM, PhD, 1st Medical Clinic for Ungulates and Small Animals, Veterinary University of Vienna, Veterinärplatz 1, Vienna 1210, Austria. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/jevs.2004.12.001 Volume 24, Number 1 29 The Expression of Messenger RNA for Tumor Necrosis Factor- ; Interleukins 1 , 6, 8, and 10; Tissue Growth Factor- ; and Interferon- in Bronchoalveolar Lavage Fluid Cells From Horses Challenged With Lipopolysaccharide and Treated With Clenbuterol R. van den Hoven, DVM, PhD, a J. C. Duvigneau, PhD, b R. T. Hartl, Dipl Biol, b K. Riedelberger, Dr Med Vet, a M. Teinfalt, Dr Med Vet, a and M. Gemeiner, PhD b Scientific Papers 10 were statistically significantly different in the three trials, indicating modulation of the LPS-induced inflam- matory response by clenbuterol treatment. The expected inhibition by clenbuterol on LPS-induced expression of TNF- mRNA or stimulation of IL-10 mRNA could not be clearly shown. However, IL-1, IL-10, and IFN- mRNA tended to be downregulated by clenbuterol in all horses; whereas IL-6 mRNA appeared to be downregu- lated in horses with small airway diseases only. Despite its limitations, this study showed that clenbuterol ap- peared to modulate the communication between the different cell types in equine airways. A different clen- buterol dosing strategy, a different sample time, and a heavier challenge might have caused more significant changes. (J Equine Vet Sci 2004;24:29-36) R ecurrent airway obstruction (RAO), formerly re- ferred to as chronic obstructive pulmonary dis- ease, is a common disease of mature stabled horses. An excellent short review of the disease was recently given. 1 Airway inflammation plays an im- portant role in the pathophysiology of the disorder. The primary lesion is bronchiolitis, characterized by accumu- lation of mucus and neutrophils in the airway lumen and peribronchial infiltration with mononuclear cells, primar- ily lymphocytes. 2 The action of neutrophilic granulocytes is considered to be the major pathologic event in equine RAO. 3 Cytokines, primarily chemokines, play a central role in lower airway inflammation and are produced by a multitude of cell types including neutrophils, macro- phages, lymphocytes, eosinophils, mast cells, dendritic cells, endothelial cells, and epithelial cells. 4 Specific cy- tokines could serve as biomarkers for the involvement of certain cell types in inflammatory and other pathologic REFEREED