Effect of coating with lung lining fluid on the ability of fibres to produce a respiratory burst in rat alveolar macrophages

The aim of the study was to develop a simple short-term in vitro assay which would allow us to predict the pathogenicity of fibres based on data already available from in vivo studies. Fibres were used naked (uncoated) or coated with rat IgG, or rat or sheep surfactant. The fibres were used to stimulate superoxide anion release by rat alveolar macrophages. Binding of fibres to rat alveolar macrophages was assessed by optical microscopy. Fibres used in the naked state produced little or no stimulation of superoxide anion from rat alveolar macrophages. When fibres were coated with rat IgG there was a significant increase in superoxide release for all fibre types with the exception of RCF4 and Code 100/475. When fibres were coated with rat or sheep surfactant, there was suppression of the respiratory burst for all fibre types. The observed suppression was not due to a scavenging effect by the surfactant itself, because xanthine/xanthine oxidase generated superoxide was unaffected by surfactant. The suppressive effect was shown to act directly on the macrophages. Comparing naked and coated fibres for their ability to bind to macrophages, it was shown that in general more coated fibres were bound and that increased binding was associated with suppressed superoxide release for both types of surfactant-coated fibres. It was concluded that the nature of the fibre coating is the main factor influencing the interaction between fibres and macrophages. The type of binding through different receptors may either stimulate or switch off the respiratory burst. The assay used here does not, however, allow any predictions to be made regarding the pathogenicity of fibres.