MONOCYTES INCUBATED WITH SURFACTANT - A MODEL FOR HUMAN ALVEOLAR MACROPHAGES

Monocytes migrate to the lungs and enter the alveoli where they come i nto contact with surfactant and differentiate into alveolar macrophage s, This study focused on the question of the extent to which monocytes and monocyte-derived macrophages (MDM) incubated with surfactant rese mble alveolar macrophages, Surfactant-incubated monocytes shared with alveolar macrophages the intracellular presence of surfactant, efficie nt phagocytosis of opsonized Staphylococcus aureus, and poor intracell ular killing of ingested bacteria, The suppressive effect of surfactan t on bactericidal activities of monocytes could not be attributed to e ither the surfactant Lipid fraction or surfactant protein A, Monocytes incubated with surfactant differed from alveolar macrophages with res pect to expression of various Fc and complement receptors involved in intracellular killing of bacteria, Surfactant-incubated monocytes prod uced significantly more H2O2 upon stimulation with phorbol ester than alveolar macrophages, but significantly less than control monocytes, T ogether, monocytes and MDM incubated with surfactant, although similar to alveolar macrophages in some aspects, are not an adequate model fo r alveolar macrophages. Most likely, factors other than surfactant in the microenvironment of the alveoli, such as oxygen tension, play a ro le in the differentiation of monocytes to alveolar macrophages as well .