Ingested Aggregates of Ultrafine Carbon Particles and Interferon-γ Impair Rat Alveolar Macrophage Function

Alveolar macrophages (AM), obtained by lavage from the rat lung, were allowed to ingest aggregated ultrafine carbon particles, about 1 μg/106 AM, which is a realistic result of long-term exposure to ambient air. The effects of the ingested carbon on the phagocytosis of test particles and oxidative metabolism of the AM were studied. In addition, the effects of short-term (40 min or 2 h) and long-term (28 or 44 h) incubation with interferon gamma (IFN-γ) on AM loaded and unloaded with carbon were investigated. Phagocytic activity was studied using fluorescein-labeled 3.2-μm silica particles. The attachment and ingestion processes were evaluated separately. The ingested carbon markedly impaired the phagocytosis of silica particles; the accumulated attachment (sum of attached and ingested particles per AM) decreased from 5.0 to 4.2 particles/AM and the ingested fraction (number of ingested particles per AM divided with accumulated attachment) from 0.42 to 0.27. The short-term incubation with IFN-γ tended to increase the accumulated attachment (from 5.0 to 5.7 particles/AM) and decreased the ingested fraction (from 0.42 to 0.34) in unloaded AM. Long-term incubation with IFN-γ markedly impaired both the accumulated attachment (to 3.8 particles/AM) and the ingested fraction (to 0.24) in unloaded AM and the carbon load further decreased the accumulated attachment to 2.8 particles/AM, and the ingested fraction to 0.21. The oxidative metabolism was not effected by the ingested carbon or the short-term incubation with IFN-γ, but the long-term incubation with IFN-γ increased it with a factor of almost 3. Our results suggest that ingested environmental particles in AM may markedly impair their phagocytic capacity, especially during long-term exposure to IFN-γ as after infections, and there might be an increased risk for additional infections. Moreover, during an episode of high ambient particle concentration the inhaled particles will not be efficiently phagocytized and may thereby damage the Lung tissue.