Effects of TNF-α on rECP-induced apoptosis. BEAS-2B cells were treated with 20 μM rECP. (A) TNF-α was measured in cell lysates by rECP treatment for ranging from 0 to 48 h. (B) TNF-α was measured in cultured supernatant medium by rECP treatment for 48 h. All the TNF-α measurements were determined by ELISA assay. (C) To investigate the role of TNF-α in rECP-induced apoptosis, BEAS-2B cells were pretreated with 5 μM anti-TNF-α Ab for 4 h before rECP treatment. The addition of IgG Ab to the medium of cells was used as controls in neutralization studies. All data represent the arithmetic mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.