Abstract
We have studied the effects of in vivo asbestos exposure on the surface immune-associated (Ia) antigen expression and distribution of alveolar macrophage subpopulations defined by continuous iso-osmotic Percoll gradients (density range: 1, 006 to 1.123 g/ml) using a rat model of asbestos inhalation. Two groups of rats were exposed by intermittent inhalation (6 hr/day for 5 days/week over 4 weeks) to either amphibole (crocidolite) or serpentine (chrysotile) asbestos. A group of control rats was sham-exposed to clean air only. Alveolar macrophages from rats of three groups were obtained by bronchoalveolar lavage. During exposure, distinct differences appeared within 7 days of asbestos exposure, and some of these findings persisted in the crocidolite-exposed group for as long as 2 to 5 months after the cessation of exposure. Furthermore, relatively greater proportions of Ia-antigen positive cells were detected in several density fractions obtained from both asbestos-exposed groups (especially the crocidolite-exposed group). Multinucleated alveolar macrophages were seen frequently in all Percoll fractions after both types of asbestos inhalation. A significant proportion of multinucleated alveolar macrophages in these fractions expressed surface Ia-antigen positivity. The finding of enriched numbers of higher-density phagocytes in bronchoalveolar lavage cell subpopulations from asbestos-exposed rats may reflect the presence of newly recruited-immature monocytes and/or macrophages at sites of intrapulmonary asbestos deposition. Also, increased proportions of Ia-antigen positive cells suggest that a part of them were functionally activated.
