Ingested aggregates of ultrafine carbon particles and interferon-gamma impair rat alveolar macrophage function

Alveolar macrophages (AM), obtained by lavage from the rat lung, were allow ed to ingest aggregated ultrafine carbon particles, about 1 mu g/10(6) AM, which is a realistic result of long-term exposure to ambient air. The effec ts of the ingested carbon on the phagocytosis of test particles and oxidati ve metabolism of the AM were studied. In addition, the effects of short-ter m (40 min or 2 h) and long-term (28 or 44 h) incubation with interferon gam ma (IFN-gamma) on AM loaded and unloaded with carbon were investigated, Pha gocytic activity was studied using fluorescein-labeled 3.2-mu m silica part icles. The attachment and ingestion processes were evaluated separately. Th e ingested carbon markedly impaired the phagocytosis of silica particles; t he accumulated attachment (sum of attached and ingested particles per AM) d ecreased 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 t o 0.27, The short-term incubation with IFN-gamma tended to increase the acc umulated attachment (from 5.0 to 5.7 particles/AM) and decreased the ingest ed fraction (from 0.42 to 0.34) in unloaded AM. Long-term incubation with I FN-gamma markedly impaired both the accumulated attachment (to 3.8 particle s/AM) and the ingested fraction (to 0.24) in unloaded AM and the carbon loa d further decreased the accumulated attachment to 2.8 particles/AM, and the ingested fraction to 0.21, The oxidative metabolism was not effected by th e ingested carbon or the short-term incubation with IFN-gamma, but the long -term incubation with IFN-gamma increased it with a factor of almost 3. Our results suggest that ingested environmental particles in AM may markedly i mpair their phagocytic capacity, especially during long-term exposure to IF N-gamma as after infections, and there might be an increased risk for addit ional infections. Moreover, during an episode of high ambient particle conc entration the inhaled particles will not be efficiently phagocytized and ma y thereby damage the lung tissue. (C) 1999 Academic Press.