Surface film formation in vitro by infant and therapeutic surfactants: role of surfactant protein B

Pulmonary surfactant provides an alveolar surface-active film that is critical for normal lung function. Our

Film formation in vitro differs among therapeutic surfactants and is highly dependent on SP-B content in infant surfactant. The results support a critical role of SP-B for promoting surface film formation.

We used a multiwell fluorescent assay measuring maximum phospholipid surface accumulation (Max), phospholipid concentration required for half-maximal film formation (½Max), and time for maximal accumulation (tMax).

Among five therapeutic surfactants, calfactant (highest SP-B content) had film formation values similar to natural surfactant, and addition of SP-B to beractant (lowest SP-B) normalized its Max value. Addition of budesonide to calfactant did not adversely affect film formation. In tracheal aspirates of preterm infants with evolving chronic lung disease, SP-B content correlated with ½Max and tMax values, and SP-B supplementation of SP-B-deficient infant surfactant restored normal film formation. Reconstitution of normal surfactant indicated a role for both SP-B and SP-C in film formation.