Submitted on October 5, 2006
Accepted on December 8, 2006
ELEVATED AMOUNT OF TOLL-LIKE RECEPTOR 4 mRNA IN BRONCHIAL EPITHELIAL CELLS IS ASSOCIATED WITH AIRWAY INFLAMMATION IN HORSES WITH RECURRENT AIRWAY OBSTRUCTION
Annerose Berndt1*, Frederik J. Derksen1, Patrick Venta2, Susan Ewart1, Vilma Yuzbasiyan-Gurkan3, and N. Edward Robinson1
1 Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States
2 Department of Microbiology and Molecular Genetics, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States
3 Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States
* To whom correspondence should be addressed. E-mail: berndtan{at}cvm.msu.edu.
Recurrent airway obstruction (RAO) is characterized by neutrophilic airway inflammation and obstruction, and stabling of susceptible horses triggers acute disease exacerbations. Stable dust is rich in endotoxin, which is recognized by Toll-like receptor (TLR) 4. In human bronchial epithelium, TLR4 stimulation leads to elevation of interleukin (IL)-8 mRNA expression. The zinc finger protein A20 negatively regulates this pathway. We hypothesized that TLR4 and IL-8 mRNA, and neutrophil numbers are elevated, and that A20 mRNA is not increased in RAOs during stabling compared to controls, and to RAOs on pasture. We measured the maximal change in pleural pressure (
Pplmax), determined inflammatory cell counts in bronchoalveorlar lavage fluid (BAL), and quantified TLR4, IL-8 and A20 mRNA in bronchial epithelium by qRT-PCR. We studied six horse pairs, each pair consisting of one RAO and one control horse. Each pair was studied when the RAO-affected horse had airway obstruction induced by stabling, and after 7, 14 and 28 days on pasture. Stabling increased BAL neutophils, Pplmax and TLR4 (fold change of 4.14) significantly in RAOs compared to controls and to RAOs on pasture. TLR4 correlated with IL-8 (R2=0.75). While stabling increased IL-8 in all horses, A20 was unaffected. IL-8 was positively correlated with BAL neutrophils (R2=0.43) and negatively with A20 (R2=0.44) only in RAO-affected horses. Elevated TLR4 expression and lack of A20 upregulation in bronchial epithelial cells from RAO-affected horses may contribute to elevated IL-8 production, leading to exaggerated neutrophilic airway inflammation in response to inhalation of stable dust.
