FIG. 1.

Caspase-independent cell death during infection of epithelial cells or monocytes with the GPIC strain of C. psittaci or the LGV/L2 strain of C. trachomatis. HeLa (A) and U937 (B) were infected with C. psittaci, at an MOI of 0.7 and 1.0, respectively, or with C. trachomatis at an MOI of 0.3, for 48 h in the presence or absence of 100 μM z-VAD-fmk. As positive controls for caspase-dependent cell death, HeLa cells were incubated with 15 μM TPEN for 17 h, and U937 cells were incubated with anti-Fas antibody (0.5 μg/ml) for 16 h. Apoptosis was measured by cytofluorimetry as described in Materials and Methods. The values represent the means and standard deviations (error bars) of three separate experiments. (C) Caspase-3 activity was measured in lysates from HeLa cells infected with C. psittaci for 48 h or treated with TPEN for 17 h, using the fluorescent substrate for caspase-3, DEVD-AFC, as described in Materials and Methods. The same level of apoptosis was measured in TPEN-treated or Chlamydia-infected cells under these conditions. The extent of DEVD-AFC cleavage in TPEN-treated cells was defined as 100, and the other values were normalized with respect to this positive control. The values represent the means and standard deviations (error bars) of three samples treated with TPEN or infected with Chlamydia on separate days.