Epithelial expression of mRNA and protein for IL-6, IL-10 and TNF-α in endobronchial biopsies in horses with recurrent airway obstruction

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-alpha, 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 (r(s) = 0.893, p = 0.007). Curiously, in controls examined on pasture the TNF-alpha protein level was positively correlated to IL-10 mRNA expression (r(s) = 0.967, p = 0.007) and negatively correlated to IL-6 mRNA expression (r(s) = -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-alpha 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-alpha are needed, as is expansion of the range of cytokines to include other key regulators of airway inflammation.