Expression of Vitamin D Receptor Gene (VDR) and Associated Cytokine Response in Arabian Horses with Chronic Inflammatory Airway Disease

INFLAMMATORY airway disease (IAD) represents inflammatory conditions of the lower respiratory tract. IAD occurs in athletic horses and is a common cause of training interruption and impaired performance. The aim of this investigation was to evaluate the relationship between the Vitamin D Receptor (VDR) gene and cytokines in horses with chronic IAD. Ten horses with IAD and five clinically healthy horses were studied. Serum levels of tumor necrosis alpha (TNF-alpha) and interleukin-113 (IL -113) were measured, and real-time PCR was used for relative quantification of the mRNA level of the VDR gene in horse blood samples. Clinically, horses under investigation suffered from IAD showing mucopurulent nasal discharge, increased respiratory rate, chronic cough, and abnormal lung and tracheal sounds. A significant increase in IL -113 (p < 0.01) and TNF (p < 0.01) levels was recorded in horses with chronic IAD compared to those in clinically healthy horses. However, VDR gene expression was significantly decreased (p < 0.001) in horses with chronic inflammatory airway disease compared to that in the controls. There was a positive correlation between IL -113 and TNF-alpha levels (r =, p = 0.001). However, a negative correlation was observed between VDR gene expression and IL -113 and TNF-alpha levels. In conclusion, the results of the present study indicate that VDR gene has a major role in the occurrence of IAD in horses. Further studies on the role of vitamin D as a preventive therapy for IAD are required in clinical practice.