Activity of TRAIL in MPM cell lines or primary cultures. Jurkat T cell leukemic cells (black column), commercially available and/or well-established MPM cell lines (grey columns) and primary MPM cultures (white columns) were incubated with 100 ng/ml His-TRAIL, and cell proliferation was determined by MTT assay 72 h thereafter. Absorbance values obtained with untreated cells maintained under identical conditions were taken as 100%. Data represent means of three independent experiments and bars indicate standard deviations. **, P < 0.01 and *, P < 0.05 compared to untreated cells.