Surfactant protein group with molecular weights 28,000 to 36,000 daltons (SP 28-36) increases the association of phospholipids with freshly isolated type II cells

Previous studies demonstrated that intratracheally-instilled radiolabelled subfractions of alveolar surfactant which contain SP 28-36 were incorporated into lamellar bodies to a greater extent than were SP 28-36-poor subfractions. The authors have characterized the effects of isolated SP 28-36 on the association of a mixture of surfactant-like synthetic lipids with isolated type II cells. Rat SP 28-36 was isolated according to modifications of the method of Hawgood et al., type II cells were isolated by differential adherence and averaged 84% pure. 267 nmol of lipid was incubated with 2.5 x 10/sup 6/ cells in 1ml of medium for 60 min. In the absence of added SP 28-36, the association of labelled dipalmitoylphosphatidylcholine (DPPC) averaged 0.67 (+/-.16) nmol DPPC/10/sup 6/ cells. SP 28-36 (15..mu..g) increased the association of DPPC to 5.01 (+/- 0.94) nmol/10/sup 6/ cells (n=4). The association was dependent on protein concentration and reached a maximum at 10..mu..g SP 28-36/ml. The effect was inhibited by the addition of polyclonal antibodies against SP 28-36. These results are consistent with a hypothesis that SP 28-36 mediates uptake of surfactant-like lipids by isolated type II cells.