Proteases and protease inhibitors of possible clinical relevance in COPD of horses

The importance of proteases and protease inhibitors for the pathogenesis of pulmonary emphysema and chronic bronchitis of the horse is described. Endogenous elastases from neutrophil granulocytes and macrophages, which probably provoke emphysema in the human being, are not relevant in horse emphysema. Exogenous elastases from different species of streptomyces may be responsible for emphysema generation in this species. Part of the exogenous elastases are poorly or not inhibited at all by the equine blood protease inhibitors especially by alpha 1-protease inhibitors. A disorder similar to genetic alpha 1-protease inhibitor deficiency in the human being could not be found in the horse. Proteases and protease inhibitors are probably also relevant for the pathogenesis of chronic bronchitis. Neutral proteases from neutrophil granulocytes may be relevant as initiators or amplifiers of an inflammation in the human being and in the horse. Under physiological conditions the proteases are controlled by the secretory protease inhibitor called HUSI-1 in the human being. In contrast, the horse lacks a protease inhibitor proper to secretion in its respiratory ducts. Protease activity, which correlates with the degree of the COPD, was detected in equine inflamed tracheobronchial secretions. This finding is useful in diagnostic evaluation of the individual disease.