Ultrastructure of phospholipid mixtures reconstituted with surfactant proteins B and D

Surfactant protein (SP)-D is secreted from pulmonary alveolar type II cells into the alveolar lumen where potential interactions with surfactant lipid s might occur. SP-D binds phosphatidylinositol (PI), a component of mammali an surfactants that is increased in a variety of injury states. We investig ated the ultrastructure and properties of lipid protein recombinants that i ncluded SP-D, PI, and SP-B and compared these with recombinants based on SP -A. SP-D had a profound effect on the organization of phospholipid vesicles containing PI and SP-B, promoting the formation of atypical but highly ord ered and surface-active tubular aggregates distinct in their dimensions and shape from the classical tubular myelin formed by SP-A. We also found both types of tubules in the secretions of type LI cells maintained in long-ter m culture. These results suggest that surface atypical tubules can be forme d with SP-D in vitro and in vivo.