Figure 5

Morphology of epithelioid granulomas after 14 days of exposure to asbestos fibers or MWCNTs in 3D cultures. After 14 days, cells were fixed in situ, embedded in plastic, and sectioned. 0.5 μm sections were stained with toluidine blue (A) for light microscopy. Magnification: 1000×. Ultrathin sections were stained with uranyl-acetate/lead citrate for transmission electron microscopy (B). Untreated cells or cells exposed to 0.5 μg/ml (0.38 μg/cm²) of carbon black have short surface microvilli and well-preserved cellular organelles. Exposure to 0.5 μg/ml (0.38 μg/cm²) of asbestos fibers or commercial MWCNTs induces epithelioid granulomas characterized by compact cell aggregates with prominent interdigitating surface microvilli. Asbestos fibers or MWCNTs are usually localized in cytoplasmic vacuoles and cellular organelles are well preserved. Black arrow and M: microvilli, N: nucleus, *: vacuole containing particulates, ER: endoplasmic reticulum.