Purification and biochemical characterization of equine pulmonary surfactant protein D

Objective-To characterize surfactant protein D (SPD) isolated from bronchoa lveolar lavage fluid (BALF) of healthy horses. Sample Population-BALF from 10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) without history or clinical signs of respiratory tract disease. Procedure-BALF was obtained and centrifuged at 33,000 X g. The supernatant was applied to a mannose-Sepharose 6B affinity column in the presence of ca lcium, and the bound protein fraction was analyzed by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblot analysis: amino aci d composition was determined and partial sequencing was done. Phospholipid binding and liposome aggregation assay were performed, using purified prote ins. Results-The protein isolated by use of mannose affinity matrices was SP-D, it bound carbohydrates and phosphatidylinositol, which are the characterist ic features of SP-D isolated from other animal species. Amino acid analysis and partial primary sequence of the isolated protein indicated high homolo gy with rat and human SP-D. Furthermore, immunoblot analysis indicated that equine SP-D reacted with human and rat SP-D-specific antibodies. Conclusion and Clinical Relevance-SP-D exists in equine lungs; its measurem ent may be useful in evaluating equine lung disease.