Enhanced in vitro PAI-1 production by PA103-infected cells. PAI-1 concentrations in supernatants from A549 epithelial respiratory cells (A) and THP-1 macrophages (B) infected with the ExoU-producing PA103 were significantly higher than concentrations detected in supernatants from control noninfected cells or from cells infected with the PA103 exoU mutant. Data represent mean values ± SE of the results obtained in three different assays carried out in quintuplicate. **p < 0.01 and *** p < 0,001 when data obtained from PA103-infected cells were compared with data from control cells and from PA104ΔexoU-infected cells, or when data obtained with PAF-treated cells were compared with those from control cells. In (C), a representative agarose gel shows the expression of PAI-1 and β-actin mRNA transcripts in control and infected A549 cells assessed by semiquantitative RT-PCR. In (D), mean ± SD values of the ratio of PAI-1 to β-actin transcript densities obtained in 2 RT-PCR assays carried out in duplicate. *, p < 0.05 and ** p < 0.01 when data obtained from PA103-infected cells were compared with those from controls and from PA103ΔexoU-infected cells.