Human alveolar macrophage phagocytic function is impaired by aggregates ofultrafine carbon particles

Alveolar macrophages (AM) were collected by bronchoalveolar lavage from hea lthy volunteers. The AM were loaded with small masses (0.03-3 mug/10(6) AM) of ultrafine carbon particle aggregates. The phagocytic activity of the ce lls was studied 20h after the loading. Fluorescein-labeled silica particles (3 mum) were used as test particles and the attachment and ingestion proce sses were studied separately. In some experiments, AM were incubated with i nterferon-gamma (IFN-gamma) for 20h before and during the test of phagocyti c activity and during measurement of oxidative metabolism. The ingested car bon particles induced a dose-related impairment of both the attachment and the ingestion processes with a marked impairment down to a carbon particle dose around 0.2 mug/10(6) AM. Such levels should reasonably occur after inh alation of existing concentrations of urban air particles, which to a consi derable extent consist of aggregates of ultrafine particles with a carbon s keleton. Incubation with IFN-gamma (12.5 U/ml) also induced significant imp airments in both the attachment and the ingestion processes. Loading with c arbon further aggravated the effect of IFN-gamma. In contrast to earlier st udies in rat AM, IFN-gamma did not impair the oxidative metabolism at rest in these human AM; instead the oxidative metabolism was increased. This dif ference was due to a difference between rat and human AM and not between ra t and human IFN-gamma. Our results suggest that ingested environmental part icles in AM, e.g., after an episode of high particle concentration, may imp air phagocytic capacity of the cells, especially after infections that indu ce an increased production of IFN-gamma. Consequently, there might be a ris k for additional infections. Moreover, inhaled particles not phagocytized b y AM might damage the lung tissue. (C) 2001 Academic Press.