FIG. 1.

Effects of LPS and rhTNF-α on apoptotic cell death in TPA-differentiated U937 cells. U937 cells were pretreated with TPA (10 ng/ml) for 12 h. (A) The TPA-differentiated U937 cells (10⁵ cells) were further treated with E. coli LPS (1 μg/ml) (▴), A. actinomycetemcomitans LPS (□), P. gingivalis LPS (▪), rhTNF-α (1 ng/ml) (•), or nothing (○) for 6 to 72 h. (B) Other TPA-differentiated U937 cells (10⁵ cells) were treated with a 1- or 10-μg/ml of LPS from E. coli, A. actinomycetemcomitans, or P. gingivalis; rhTNF-α (1 ng/ml); or nothing for 24 h. After each treatment, apoptosis induced in the cells was evaluated by morphological assessment using Hoechst 33258 dye, as described in Materials and Methods. Values shown (percent apoptotic cells) are the means ± SD (error bars) of three separate experiments, each conducted in triplicate. Differences from the value for untreated cells (vehicle) were considered significant (**) at a P of <0.01.