FIG. 4.

Reversal by tryptophan of IFN-γ-dependent inhibition of apoptosis. HeLa cells were infected with C. muridarum at an MOI of 0.5 for 48 h. Infected cells were treated with (white bars) or without (black bars) IFN-γ (2 ng/ml) and with or without 200 μg of l-tryptophan per ml. Apoptosis was measured by cytofluorimetry using PI-stained, detergent-permeabilized cells, as described in Materials and Methods. The values were normalized to the highest level of apoptosis (infected cells in the absence of IFN-γ or l-tryptophan), and the values are means and standard deviations for three samples infected with C. muridarum on separate days.