Morphology of HEp-2 cells. (a) Untreated HEp-2 cells, and HEp-2 cells after 6 hours of exposure to (b) hydrogen peroxide (H2O2), (c) 2 μM staurosporine (STS), and (d) 10 μM STS. Images were acquired using an Olympus IX-70 microscope equipped with Hoffman modulation contrast. (e) Time-dependent loss of HEp-2 cytoplasmic membrane integrity in control cells (open circles) and cells exposed to 0.1% H2O2 (triangles), to 2 μM STS (diamonds), and to 10 μM STS (squares). The loss of cytoplasmic membrane integrity, indicative of necrosis, was quantified using the trypan blue exclusion assay. Values are the mean ± standard deviation from three independent experiments.