TNF-α release and induction of caspase-3 activity and TNF receptor 1 expression during the exposure of Daudi cells to IFN-α.

(A) TNF-α concentration (pg/mL) was determined by ELISA in culture supernatants collected 5, 15, 30, and 60 minutes and 3, 6, 24, 48, and 72 hours after incubation with IFN-α (▪) or without IFN-α (▴). Caspase-3 activity was analyzed as described in “Materials and methods.” Daudi cells were treated with IFN-α at the same time points as for the ELISA. Uninduced cells were used as a control (shown as 100% of baseline [dotted line]). Caspase-3 activity is expressed as a percentage of optical density of the control cells (●). (B) Expression of TNF receptor 1 (p55) in absence or presence of IFN-α. Cells were incubated without or with 200 U/mL IFN-α as before. TNF receptor 1 expression was measured by flow cytometry applying the Kolmogorov-Smirnov statistics expressed by the D value.