Functional Analyses of the Molecular mechanisms Underlying Two Equine Respiratory Diseases: Recurrent Airway Obstruction and Rhodococcus equi Pneumonia

Abstract

Recurrent airway obstruction (RAO) and Rhodococcus equi (R. equi) pneumonia are two equine respiratory diseases. RAO is an allergic asthma like disease of the middle-aged horses while the R. equi pneumonia affects only young foals. Respiratory disease is considered among the major causes of economic loss to the equine industry and tops the priority list for research that will focus on preventative and diagnostic facets of such disease. The objective of this research was to investigate the effect of antigen exposure and remission (via allergen avoidance and/or drug) on chronically affected RAO horses. Additionally, we also wanted to understand the changes in equine neonatal immune system due to R. equi exposure and identify molecular biomarkers for early disease screening. Various biological samples (lung tissue for the RAO study and blood leukocytes and nasal epithelial cells for the R. equi study) were used to extract ribonucleic acid (RNA). Complimentary deoxyribonucleic acid (cDNA) obtained from RNA was used to perform microarray hybridization experiments.

Our findings suggest that compared to control horses allergen exposure leads to an elevated protein synthesis and inflammation that contributes to aggravation of symptoms and airway changes. We found that allergen avoidance controls inflammation and causes an improvement in lung function and other chronic features of RAO. The drug administration led to an accelerated remission in the chronic RAO features; a complete remission could however not be achieved. Hence it appears that although not a complete resolution, but allergen avoidance and drugs will help in a better management of chronic RAO symptoms.

Our results suggest that the neonatal immune system is capable of initiating a protective immune response through birth up to 8 weeks of age. However there are also processes present that may be counter-productive to the host. Induction of such suppressive mechanisms may be a result of bacterial modulation of the host immune response or a result of immature host immune system. We also identified molecular biomarkers that will have the potential to screen foals for R. equi pneumonia soon after birth and before the onset of clinical symptoms. The research findings of this study will improve the current understanding of the two equine diseases.