Morphology and function of blood monocytes after incubation with lung surfactant

Human blood monocytes were incubated for different periods of time with lung surfactant (phospholipid concentration 1-2.5 mg/ml). After short-term (30 min) incubation, there was an increase in the nitroblue tetrazolium (NBT) reduction of the monocytes both at rest and during stimulation with E. coli bacteria, and enhanced ingestion of fluorescein-labelled yeast particles. Electron microscopic examination of the same monocytes showed an active cell surface with numerous protrusions. Long-term (24 h) incubation with surfactant resulted in a reduced ability of the cells to adhere to plastic dishes. Although the NBT-reduction of resting monocytes was increased after long-term incubation with surfactant, the additional enhancement of NBT-reduction after stimulation with bacteria was decreased. These cells were rounded, usually devoid of surface structures, their nuclei were condensed, and their cytoplasm filled with surfactant material. Thus, monocytes are initially activated in the presence of surfactant, but if the cells become overfed with surfactant lipids their functional capacity decreases.