The effect of increased particles on the endocytosis of radiocolloids by pulmonary macrophages in vivo: competitive and toxic effects.

We have developed a technique for measuring the rate of particle ingestion by pulmonary macrophages in vivo. This technique has been used to examine the impact of pre-exposure to ferric oxide, colloidal carbon, and coal dust on the endocytosis of a test particle, colloidal gold. Our technique for estimating endocytosis is as follows: Syrian golden hamsters received intratracheal instillations (0.15 cm3/100 g body weight) of a suspension of colloidal 198Au (approximately 30 nm diameter). Two hours following instillation, each hamster was sacrificed and its trachea cannulated. The lungs were lavaged 12 times with saline solutions, and the number of cells and gold particles in each wash determined. Analysis of the washout curves permits the calculation of the fraction, gamma, of the colloidal particles which has been ingested at a time, t. This method was then used to measure the influence of inhaled or intratracheally instilled particles on the endocytosis of the gold particles. Hamsters breathed ferric oxide aerosol spontaneously or were given intratracheal instillations of colloidal carbon or coal dust. Immediately following the exposure, the ability of the macrophages to ingest a test particle was assayed by the technique described above. In all instances, colloidal gold endocytosis measured at 2 h was significantly depressed. However, when challenged by the gold colloid 24 h after exposure to the inhaled or instilled particles, only the coal dust group exhibited depressed endocytosis. We conclude that all dusts studied competitively inhibit endocytosis, but only some exhibit a toxic effect on macrophage function.