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 extraction with 1-butanol, and organic solvent-insoluble protein precipitates were dialyzed against Tris buffer. The suspension was centrifuged, and supernatant was placed in a mannose-Sepharose affinity column, with calcium. The bound protein fraction was analyzed by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western immunoblot analysis, and amino acid sequencing. A liposome-aggregation assay was also performed, using purified proteins. RESULTS: Protein isolated by use of mannose-affinity matrices was identified as surfactant protein A (SP-A). It had carbohydrate-binding and phospholipid-aggregation properties characteristic of SP-A isolated from other animal species. The partial primary sequence of the isolated protein had high homology with rat and human SP-A. Furthermore, the equine SP-A reacted with anti-human and anti-rat SP-A specific antibodies. CONCLUSION: Analysis of these findings indicated the existence of SP-A in pulmonary tissues of horses. CLINICAL RELEVANCE: Measurement of SP-A concentrations may be useful for clinicians evaluating pulmonary disease of horses.