FIG. 3.

Cell death of HS-72 cells induced by the toxin from A. actinomycetemcomitans Y4. HS-72 cells (2 × 10⁴) were cultured with partially purified toxin (5, 25, and 50 μg/ml) for 48 h (A); HS-72 cells were cultured with the partially purified toxin (50 μg/ml) for 12, 24, 36, and 48 h (B). Percent cytotoxicity was determined by the MTT viability assay as described in Materials and Methods. Data are expressed as means ± standard deviations of triplicate determinations. The experiment was performed three times, with similar results.