ULTRASTRUCTURE OF LUNG IN SURFACTANT PROTEIN-B DEFICIENCY

Congenital alveolar proteinosis (CAP), a cause of respiratory failure in full-term newborns, often leads to death in infancy despite medical therapy. We recently described an inherited deficiency of surfactant protein B (SP-B) (N. Engl. J. Med. 1993; 328:406-410) in two siblings with CAP. The SP-B deficiency was accompanied by marked abnormalties, both quantitative (increase) and qualitative (distribution), of SP-A a nd SP-C in the lungs of the affected infants. Ultrastructural studies of the lung of one of these infants and of a third affected sibling bo rn in the index family showed abundant alveolar concentric multilamell ated structures and membranous vesicles but no typical tubular myelin. In addition, membranous vesicles from type II cells and immunogold la beled SP-A and SP-C were found between type II cells and their basemen t membrane despite intact interepithelial cell junctions. These findin gs suggest an important role for SP-B in the directionality of surfact ant secretion and in the formation of tubular myelin.