A simple, fast, precise and biologically relevant toxicity assay for screening cytotoxicity of minerals would have distinct advantages due to its cost benefits and relative savings in time. Furthermore, a bioassay to differentiate acute and chronicin vivo pulmonary reactions could have potential value as predictors of fibrogenicity and pathogenicity. In this study we examined the potential use of lucigenin as a probe to evaluate the correlation between chemiluminescence (CL) generated by alveolar macrophages with the known cytotoxicity and pathogenicity by conventional bioassays. In this study, we used small doses of dust (20 μg) to minimize cellular overload and to maintain homeostasis. Crystalline silica a highly fibrogenic dust was used as positive control and results are compared with those for bentonite, kaolin and talc. Among the three minerals compared with silica, bentonite was more reactive (27%) in CL assay and declined sharply compared to other minerals. This sudden decline in bentonite CL is caused by cytotoxicity leading to cell death. CL-induced by talc was comparable to silica and declines slowly. Kaolin on the other hand produced relatively a weaker (25%) CL compared to silica. Our data using relatively low doses of dust suggest that the CL assay may have a better predictive value in cytotoxicity evaluations compared to conventional toxicity assays.

Effect of lipopolysaccharide (LPS) on RAW264.7 macrophage cell line was studied. LPS-treated RAW264.7 cells increased in cell size and acquired distinct dendritic morphology. At the optimal dose of LPS (1 μg/ml), almost 70% RAW264.7 cells acquired dendritic morphology. Flow cytometric studies indicate that the cell surface markers known to be expressed on dendritic cells and involved in antigen presentation and T cell activation (B7.1, B7.2, CD40, MHC class II antigens and CD¹d) were also markedly upregulated on LPS-treated RAW264.7 cells. Our results suggest the possibility that LPS by itself could constitute a sufficient signal for differentiation of macrophages into DC-like cells.