Purification and biochemical characterization of pulmonary surfactant protein A of horses

Objective-To characterize surfactant protein isolated from bronchoalveolar lavage fluids of healthy horses. Animals-10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) that did not have a history or clinical signs of respiratory tract disease. Procedure-Bronchoalveolar lavage fluid (BALF) was obtained and centrifuged at 33,000 X g. Lipid was removed from precipitated fractions by means of ex traction with l-butanol, and organic solvent-insoluble protein precipitates were dialyzed against Tris buffer. The suspension was centrifuged, and sup ernatant was placed in a mannose-Sepharose affinity column, with calcium. T he bound protein fraction was analyzed by means of sodium dodecyl sulfate-p olyacrylamide gel electrophoresis, western immunoblot analysis, and amino a cid sequencing. A liposome-aggregation assay was also performed, using puri fied proteins. Results-Protein isolated by use of mannose-affinity matrices was identified as surfactant protein A (SP-A). It had carbohydrate-binding and phospholip id-aggregation properties characteristic of SP-A isolated from other animal species. The partial primary sequence of the isolated protein had high hom ology with rat and human SP-A. Furthermore, the equine SP-A reacted with an ti-human and anti-rat SP-A specific antibodies. Conclusion-Analysis of these findings indicated the existence of SP-A in pu lmonary tissues of horses. Clinical Relevance-Measurement of SP-A concentrations may be useful for cli nicians evaluating pulmonary disease of horses.