Importantly, in a study of COPD, the relative amounts of MUC5AC and MUC5B were shown to differ in smokers with and without airway obstruction [26], suggesting that this mucin composition of mucus is a major factor for efficient mucus transport. CTNND1 Other studies have analysed the expression of in horses with RAO and have yielded contradictory data, with an increase, or no switch in expression being reported [55], [56]. 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 switch 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 Cucurbitacin IIb there is a significant increase in Muc5b and Muc5ac in mucus accumulated in equine airways and these increases correlated with the numbers of bacteria. Introduction 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) Cucurbitacin IIb and chemical (particles and pollutant gases), which can then be removed from the airways by mucociliary clearance. The two most common inflammatory respiratory syndromes Cucurbitacin IIb 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. RAO, associated with chronic exposure to environmental allergens, predominantly affects middle-aged to older (usually 7 years old) housed horses [1] with the prevalence of the condition increasing with age [1], [2], [3], [4]. Reduced airflow is usually associated with bronchoconstriction, mucus hypersecretion and airway neutrophilia [2], [5], [6], [7], [8]. Clinical indicators range from slight exercise intolerance to dyspnoea at rest. Episodes may be reversed or alleviated by drug therapy or changes to management resulting in improved air quality [5], [9], [10]. Small racehorses in training suffer from IAD, a condition that also entails airway neutrophilia and increased amounts of tracheal mucus [11], [12], [13], [14]. Clinical indicators of IAD include coughing [11], [12] and poor racing overall performance [15], [16], [17], [18], [19]. We have shown previously that Muc5b and Muc5ac are the predominant mucins in airway secretion from healthy horses [20]. However, while mucus accumulation in the airways is usually associated with IAD and RAO and contributes to the pathological symptoms, little is currently known concerning the gel-forming mucins in these conditions and how they contribute to the aberrant clearance of mucus. As in the horse, the orthologous mucins, MUC5B and MUC5AC, are the major gel-forming mucins in human airway mucus [21], [22]. In normal airway epithelium the expression of the two mucins is usually cell specific; MUC5B is mainly expressed by the submucosal glands, and MUC5AC expressed by the goblet cells at the surface epithelium [22], [23]. In human Cucurbitacin IIb pathological conditions, such as asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF), mucin expression is usually altered with an increase in the amounts of both MUC5B and MUC5AC. Furthermore, MUC5B was more abundant in mucus obstructing the airways [24], [25], [26]. In addition, studies have also shown that this regulation of these two mucins can be altered by inflammatory mediators such as cytokines, and directly by external difficulties such as bacteria [27], [28], Cucurbitacin IIb [29], [30], [31]. The studies on human airway mucus have highlighted that this gel-forming mucin composition and concentration in mucus likely impacts on its efficient clearance from your respiratory tract. While in-roads have been made in the understanding of human airway mucus there are many unanswered questions relating to equine airway mucins and mucus. For example, what are the sites of.