Influence of plasma and inflammatory proteins on the ultrastructure of exogenous surfactant

We tested the hypothesis that albumin, fibrinogen and eosinophilic cationic protein (ECP) alter not only the function but also the ultrastructural composition of natural bovine surfactant (Alveofact). Therefore, natural bovine surfactant was mixed with equimolar concentrations of these proteins for 2 h and prepared for electron microscopical examination. Volume fractions, the volume to surface ratio and the volume-weighted mean volume were determined by using various stereological methods. Alveofact surface activity was tested with the capillary surfactometer. Native Alveofact-suspension contained mainly multilamellar bodies (numerous concentric predominantly fused compact phospholipid lamellae) and small fractions of multilamellar vesicles (several concentrically arranged lamellae with a less dense order) and unilamellar vesicles (one to two concentrically arranged phospholipid lamellae), but no tubular myelin. Addition of proteins to Alveofact led to a protein-dependent alteration in the distribution patterns of surfactant subtypes. The significant highest decrease in the volume fraction of multilamellar bodies was found in Alveofact-fibrinogen preparations and the lowest decrease was in Alveofact-albumin preparations. Interaction of Alveofact with ECP resulted in a significant decrease in the size of multilamellar bodies and a significant increase in the volume fraction of very small unilamellar and electron-dense vesicles. Alveofact with ECP kept test capillaries open for the shortest time, while Alveofact with albumin had little inhibitory effect. There was a significant correlation between percentage of capillary openness and the volume fraction quotient of inactive to active surfactant subtypes. Thus, equimolar concentrations of different proteins in Alveofact induce a conversion of multilamellar bodies combined with a decrease in surface activity. The most impressive structural alterations were found after mixture with ECP.