OBJECTIVES--Mounting evidence suggests that asbestos fibres can stimulate alveolar macrophages to generate the potent inflammatory and fibrogenic mediator, tumour necrosis factor-alpha (TNF-alpha), and that this may play an important part in the onset and development of airway inflammation and lung fibrosis due to asbestos fibre inhalation. Little is known, however, about the ability of other mineral fibres to initiate formation and release of TNF-alpha by alveolar macrophages. Therefore the effects of different fibres (crocidolite, chrysotile A, chrysotile B, two man made mineral fibres (MMVF 21 and MMVF 22), a ceramic fibre (RCF 1), and a silicon carbide whisker fibre (SiCwh)) on formation and release of TNF-alpha by rat alveolar macrophages were examined. METHODS--Cells were isolated and incubated at 37 degrees C with the different fibres, or with culture medium alone (controls), and the amounts of TNF-alpha messenger RNA (mRNA) in the cells and TNF-alpha bioactivity released into the culture medium were measured at different time points. RESULTS--Significantly (P < 0.05 v control) increased amounts of TNF-alpha mRNA were found in cells exposed to crocidolite, chrysotile A, chrysotile B, MMVF 21, RCF 1, or SiCwh for 90 minutes, and significantly (P < 0.05 v control) increased activities of TNF-alpha were found in the medium of macrophages exposed to crocidolite, chrysotile A, chrysotile B, or MMVF 21 for four hours. CONCLUSION--These observations suggest that not only natural mineral fibres but also certain man made mineral fibres are able to induce the formation and release of TNF-alpha by alveolar macrophages in vitro.
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