FIG. 7.

Rapid temperature-independent induction and persistence of cellular resistance to infection. Panel A: cell resistance is induced rapidly. Cultures in strip-well plates were exposed to 30 μM TAT-Cd⁻ (•) or incubated with no peptide (○) at 37°C for the times indicated. Free peptide was removed by rinsing three times over a period of <5 min, and cells were infected with hrR3 (MOI, 0.04) in the absence of peptide, treated with pH 3 citrate buffer, and scored after X-Gal staining 8 h later. Cultures not incubated at 37°C (0 time points) were exposed to peptide at ∼23°C for <1 min before they were rinsed and infected. Panel B: induction of cellular resistance is not temperature dependent. Effects of cell pretreatments with TAT-Cd⁻ for 1 h at 4 (○) or 37°C (•) were measured as described for panel A. Panel C: recovery of susceptibility to infection under normal culture conditions. Mock-treated cultures (○) and cultures exposed to 30 μM TAT-Cd⁻ (•) for 1 h at 37°C were infected and scored for infectivity as described for panel A. Panel D: cell resistance is lost by rinsing with hypertonic medium. Cultures exposed to bTAT-Cd⁻ for 1 h at 37°C were rinsed three times for 10 min at 4°C with peptide-free, serum-supplemented DMEM in the absence (○) or presence (•) of 0.5 M NaCl before they were infected as described for panel A. Infectivity was scored by measuring β-galactosidase activity in cell lysates 6 h postinfection. The data points represent the means of triplicate determinations with standard errors of the means.