Page 1 of 7 (page number not for citation purposes) BMC Veterinary Research Research article Open Access Epithelial expression of mRNA and protein for IL-6, IL-10 and TNF-α in endobronchial biopsies in horses with recurrent airway obstruction Miia Riihimäki*1,6, Amanda Raine2, Jamshid Pourazar3, Thomas Sandström3, Tatiana Art4, Pierre Lekeux4, Laurent Couëtil5 and John Pringle1 Address: 1Department of Clinical Sciences, Equine Internal Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden, 2Dept. of Cell & Molecular Biology, Biomedical Centre, Uppsala, Sweden, 3Department of Respiratory Medicine and Allergy, University Hospital, Umeå, Sweden, 4Equine Sports Medicine Centre, Faculty of Veterinary Medicine, University of Liège, Belgium, 5Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN, USA and 6Department of Clinical Sciences, Section of Large Animal Surgery and Medicine, Equine Internal Medicine, Swedish University of Agricultural Sciences, Box 7054, SE-750 07 Uppsala, Sweden Email: Miia Riihimäki* - Miia.Riihimaki@kv.slu.se; Amanda Raine - Amanda.Raine@icm.uu.se; Jamshid Pourazar - jamshid.pourazar@lung.umu.se; Thomas Sandström - thomas.sandstrom@lung.umu.se; Tatiana Art - Tatiana.Art@ulg.ac.be; Pierre Lekeux - Pierre.Lekeux@ulg.ac.bc; Laurent Couëtil - couetill@purdue.edu; John Pringle - John.Pringle@kv.slu.se * Corresponding author Abstract Background: The aim of this study was to evaluate the contribution of bronchial epithelium to airway inflammation, with focus on mRNA and protein expression of cytokines of innate immunity IL-6, IL-10 and TNF-α, in horses with Recurrent Airway Obstruction (RAO) during exacerbation and in remission. Results: Despite marked clinical and physiologic alterations between exacerbation and after remission in the RAO horses no differences were detected in either cytokine mRNA or protein levels. Moreover, the expression of investigated cytokines in RAO horses on pasture did not differ from controls. In comparing real-time PCR analysis to results of immunohistochemistry only IL-10 mRNA and protein levels in RAO horses on pasture were significantly correlated (rs = 0.893, p = 0.007). Curiously, in controls examined on pasture the TNF-α protein level was positively correlated to IL-10 mRNA expression (rs = 0.967, p = 0.007) and negatively correlated to IL-6 mRNA expression (rs = -0.971, p = 0.001). Conclusion: Given the complementary relationship of assessing cytokines directly by immunohistochemistry, or indirectly by PCR to mRNA, the lack of significant changes in either mRNA or protein levels of IL-6, IL-10 or TNF-α mRNA in RAO horses in exacerbation suggests that these particular cytokines in bronchial tissue may not play a substantive role in the active inflammation of this disease. To support this contention further studies examining time dependency of expression of IL-6, IL-10 or TNF-α are needed, as is expansion of the range of cytokines to include other key regulators of airway inflammation.

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