Abstract
Mucus accumulation is a feature of inflammatory airway disease in the horse and has been associated with reduced performance in racehorses. In this study, we have analysed the two major airways gel-forming mucins Muc5b and Muc5ac in respect of their site of synthesis, their biochemical properties, and their amounts in mucus from healthy horses and from horses with signs of airway mucus accumulation. Polyclonal antisera directed against equine Muc5b and Muc5ac were raised and characterised. Immunohistochemical staining of normal equine trachea showed that Muc5ac and Muc5b are produced by cells in the submucosal glands, as well as surface epithelial goblet cells. Western blotting after agarose gel electrophoresis of airway mucus from healthy horses, and horses with mucus accumulation, was used to determine the amounts of these two mucins in tracheal wash samples. The results showed that in healthy horses Muc5b was the predominant mucin with small amounts of Muc5ac. The amounts of Muc5b and Muc5ac were both dramatically increased in samples collected from horses with high mucus scores as determined visually at the time of endoscopy and that this increase also correlated with increase number of bacteria present in the sample. The change in amount of Muc5b and Muc5ac indicates that Muc5b remains the most abundant mucin in mucus. In summary, we have developed mucin specific polyclonal antibodies, which have allowed us to show that there is a significant increase in Muc5b and Muc5ac in mucus accumulated in equine airways and these increases correlated with the numbers of bacteria.
Highlights
The gel-forming, epithelial mucins are large polymeric glycoproteins that are a major structural component of the mucus barrier, which forms a protective interface against the external environment
Our aims were to develop antibody probes specific for Muc5b and Muc5ac in order to determine the sites of synthesis of Muc5ac and Muc5b in equine upper airways, to characterise the biochemical properties of the two mucins, and to determine the relative amounts of Muc5ac and Muc5b in mucus collected from horses with and without signs of mucus hypersecretion
Salivary and gastric tissues were studied since Real-Time (RT) PCR data showed that Muc5ac was highly expressed in gastric tissue and Muc5b was not detected, whereas Muc5b was expressed in salivary glands and Muc5ac was not detected (Table 1)
Summary
The gel-forming, epithelial mucins are large polymeric glycoproteins that are a major structural component of the mucus barrier, which forms a protective interface against the external environment Their major role is to maintain hydration of the airway epithelium and to provide a milieu to entrap external agents, both biological (allergens and bacteria) and chemical (particles and pollutant gases), which can be removed from the airways by mucociliary clearance. The two most common inflammatory respiratory syndromes of horses are recurrent airway obstruction (RAO) and inflammatory airway disease (IAD). These conditions are characterized by airway mucus over-production and impairment in mucociliary clearance. Clinical signs of IAD include coughing [11,12] and poor racing performance [15,16,17,18,19]
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