In Vitro Bioactivity of Asbestos for the Human Alveolar Macrophage and its Modification by IgG

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Abstract
The alveolar macrophage (AM) is likely to play a central role in the initiation and development of the fibrosis associated with asbestos exposure due to its ability to produce factors that modulate cellular functions of the immune system of the lung. In this study, we examine the effects of IgG, albumin, and dipalmitoylphosphatidylcholine (DPPC), the major protein and lipid constituents of alveolar lining fluid, on the interaction between the human AM and chrysotile and crocidolite asbestos, silica, and aluminum beads. We show that both chrysotile and crocidolite asbestos, but not silica and aluminum beads, stimulate the human AM to produce superoxide anion. Preincubating chrysotile and crocidolite asbestos with IgG resulted in an enhancement of their ability to stimulate superoxide anion production. IgG subclasses were studied to determine the subclass specificity of this enhancing effect; on a molar basis, IgG1 was the most potent. After preincubation with IgG, both silica and aluminum also stimulated superoxide anion production to levels similar to the IgG-preincubated asbestos. When albumin and DPPC were included in the preincubation mixture, the IgG-mediated enhancement of superoxide anion production by asbestos was unaffected, while that of silica and aluminum was abolished. In summary, these results indicate that IgG can significantly enhance the bioactivity of particulates for human AM in vitro, and that chrysotile and crocidolite asbestos are unique in their ability to retain this enhancement in the presence of albumin and DPPC. These results are consistent with the suggestion that superoxide anion production by the AM may play an important role in the development of asbestosis.