Surfactant protein SP-B counteracts inhibition of pulmonary surfactant by serum proteins.

In addition to the primary surfactant deficiency in newborns with respiratory distress syndrome (RDS), in the later course of RDS substantial protein leakage into the alveolar spaces can occur by damage to the alveolocapillary membrane. Acute lung injury results in surfactant dysfunction due in part to inhibition by serum proteins. The aim of this study was to investigate the influence of SP-B on the inhibitory effects of albumin (alb) and fibrinogen (fib) on the surface activity of pulmonary surfactant, using a) surface tension measurement with the pulsating bubble surfactometer in suspensions and b) in surfactant films applying the hypophase exchanger. After hypophase exchange a preformed film of Survanta is very resistant to the inhibitory activity of alb or fib. The surface tensions of suspensions are significantly higher (p <0.001) than the surface tensions of preformed surfactant films if alb or fib were added, e.g., 42 (41 to 43) mN/m vs. 21 (19 to 22) mN/m for Survanta with 20 mg alb/ml. After additional supplementation of Survanta with SP-B the surface activity of Survanta/1% SP-B films did not show inhibition by fib (2 mg/ml), (surface tension 8 (4 to 13) mN/m). These results indicate that SP-B can play an important role to protect the pulmonary surfactant film from inactivation by serum proteins.