IPF fibroblasts (n = 7) were treated with or without Fas-Ab in the presence or absence of CHX (250 ng/ml), with the Smac/DIABLO mimetics (SM164, 100 nM or AT406, 1.0 μM), or with the Smac/DIABLO mimetics alone for 16 hours, and apoptosis was assessed by ELISA detection of histone-associated DNA fragments. Each experiment was indexed to Fas-Ab–treated cells in the absence of any inhibitor. *P < 0.01 versus untreated or Fas-Ab–treated cells. **P < 0.001 versus untreated or Fas-Ab–treated cells. NS = not significantly different from untreated cells.