Lack of cytotoxic effects of TRAIL on osteoclastic precursors. Adherent PBMCs and RAW264.7 cells were cultured in the absence or presence of TRAIL. (A) PBMCs were let to adhere for 3 days and then were exposed to TRAIL for 48 hours. Cultures were examined for apoptosis and cell viability by light microscopy (top panels) and by DAPI staining and fluorescence microscopy (bottom panels). Shown are single fields that are representative of untreated and TRAIL-treated cultures. Original magnification, × 20. (B) The number of viable cells was scored in at least 6 random fields at × 10 magnification of PBMCs and RAW264.7 cells after 12 days of culture. Data represent the means ± SD of 7 different experiments for each cell system.