Ered significant.Enterohemolysin Induced Release of IL-1bFigure 2. Cytotoxicity of human macrophages as indicated by the release of lactate dehydrogenase (LDH). Differentiated THP-1 cells were exposed to different bacterial strains (EDL933, DpO157, DehxA, DehxA/pehxA) for 2 and 4 h. The release of LDH was assessed at specific times during incubation. Data are shown as mean 6 S.D. of experiments performed in triplicate. Significant differences (* P,0.05) are indicated. n.s., no significant differences (P.0.05). doi:10.1371/journal.pone.0050288.gFigure 1. Construction of the Met-Enkephalin site ML-281 mutant strains. (A) The genes 15900046 ehx and ecf were detected in EDL933 but not in DpO157. 
Lane M: marker; Lanes 1 and 3: EDL933; Lanes 2 and 4: DpO157 mutant. (B) Comparison of genomic DNA of EDL933 and DpO157 using 1326631 PFGE of XbaI-digested. Lane M: marker; Lane 1: EDL933; Lane 2: DpO157 mutant. (C) Using primer ehxA-3,4, EDL933 was amplified as a <3.3 kb fragment. DehxA and DehxA/pehxA were amplified as a reduced fragment to <1.6 kb. Using primer ehxA-5,6, DehxA showed no PCR product. EDL933 and DehxA/pehxA were amplified as a <360 bp fragment. Lane 1: EDL933; Lane 2: DehxA; Lane 3: DehxA/pehxA. doi:10.1371/journal.pone.0050288.gsignificantly higher levels of mature-form IL-1b (p17) in the supernatant than cells stimulated by its virulence plasmid elimination derivative strain DpO157 or its ehxA gene deletion mutant DehxA (Figure 4). The reduced release of mature IL-1b (p17) from the ehxA gene deletion mutant was restored when complemented with ehxA gene (DehxA/pehxA) (Figure 4). However, neither the expression of intracellular IL-1b mRNA (Figure S1) nor pro-IL-1b protein in cell lysis differed across the four strains (Figure 4). Overall, these results suggest that EhxA encoding on pO157 was responsible for the higher levels of extracellular production of mature IL-1b in THP-1 cells but had no effect on intracellular production of biologically inactive pro-IL-1b in THP1 cells.EHEC O157:H7-Ehx Induced IL-1b Release in THP-1 CellsThe IL-1b production in the supernatants of cell culture and cell extract infected with different bacterial strains (EDL933, DpO157, DehxA, DehxA/pehxA) was tested by ELISA and Western-blot. The ELISA results showed that the THP-1 cells stimulated by EDL933 produced higher level of IL-1b in supernatant compared with the cells stimulated by its virulence plasmid elimination derivative strain DpO157 (P,0.05), and its ehxA gene deletion mutant DehxA (P,0.05). The reduced release of IL-1b from the ehxA gene deletion mutant can be restored when complemented with ehxA gene (DehxA/pehxA) (P,0.05) (Figure 3A). We also assessed production of IL-6, IL-8, RANETS/CCL5, MCP-1, TNF-a, and IFN-c in THP-1 cells stimulated by those strains, and results showed that EhxA had no effect on production of the other cytokines we examined (Figure 3B ). To confirm whether the presence of IL-1b production we analyzed in the supernatant using ELISA was the biologically active mature form or the biologically inactive pro-IL-1b, which can be released passively during cell lysis due to cytotoxicity, we examined the production of pro-IL-1b and mature-form IL-1b in both supernatants and cell lysis using immunoblotting after the cells had been infected with different strains (EDL933, DpO157, DehxA, and DehxA/pehxA). Results showed that the IL-1b in the supernatant was mainly mature-form p17 and the IL-1b in the cell lysis was mainly inactive-form pro-IL1b, as shown in Figure 4. We als.Ered significant.Enterohemolysin Induced Release of IL-1bFigure 2. Cytotoxicity of human macrophages as indicated by the release of lactate dehydrogenase (LDH). Differentiated THP-1 cells were exposed to different bacterial strains (EDL933, DpO157, DehxA, DehxA/pehxA) for 2 and 4 h. The release of LDH was assessed at specific times during incubation. Data are shown as mean 6 S.D. of experiments performed in triplicate. Significant differences (* P,0.05) are indicated. n.s., no significant differences (P.0.05). doi:10.1371/journal.pone.0050288.gFigure 1. Construction of the mutant strains. (A) The genes 15900046 ehx and ecf were detected in EDL933 but not in DpO157. Lane M: marker; Lanes 1 and 3: EDL933; Lanes 2 and 4: DpO157 mutant. (B) Comparison of genomic DNA of EDL933 and DpO157 using 1326631 PFGE of XbaI-digested. Lane M: marker; Lane 
1: EDL933; Lane 2: DpO157 mutant. (C) Using primer ehxA-3,4, EDL933 was amplified as a <3.3 kb fragment. DehxA and DehxA/pehxA were amplified as a reduced fragment to <1.6 kb. Using primer ehxA-5,6, DehxA showed no PCR product. EDL933 and DehxA/pehxA were amplified as a <360 bp fragment. Lane 1: EDL933; Lane 2: DehxA; Lane 3: DehxA/pehxA. doi:10.1371/journal.pone.0050288.gsignificantly higher levels of mature-form IL-1b (p17) in the supernatant than cells stimulated by its virulence plasmid elimination derivative strain DpO157 or its ehxA gene deletion mutant DehxA (Figure 4). The reduced release of mature IL-1b (p17) from the ehxA gene deletion mutant was restored when complemented with ehxA gene (DehxA/pehxA) (Figure 4). However, neither the expression of intracellular IL-1b mRNA (Figure S1) nor pro-IL-1b protein in cell lysis differed across the four strains (Figure 4). Overall, these results suggest that EhxA encoding on pO157 was responsible for the higher levels of extracellular production of mature IL-1b in THP-1 cells but had no effect on intracellular production of biologically inactive pro-IL-1b in THP1 cells.EHEC O157:H7-Ehx Induced IL-1b Release in THP-1 CellsThe IL-1b production in the supernatants of cell culture and cell extract infected with different bacterial strains (EDL933, DpO157, DehxA, DehxA/pehxA) was tested by ELISA and Western-blot. The ELISA results showed that the THP-1 cells stimulated by EDL933 produced higher level of IL-1b in supernatant compared with the cells stimulated by its virulence plasmid elimination derivative strain DpO157 (P,0.05), and its ehxA gene deletion mutant DehxA (P,0.05). The reduced release of IL-1b from the ehxA gene deletion mutant can be restored when complemented with ehxA gene (DehxA/pehxA) (P,0.05) (Figure 3A). We also assessed production of IL-6, IL-8, RANETS/CCL5, MCP-1, TNF-a, and IFN-c in THP-1 cells stimulated by those strains, and results showed that EhxA had no effect on production of the other cytokines we examined (Figure 3B ). To confirm whether the presence of IL-1b production we analyzed in the supernatant using ELISA was the biologically active mature form or the biologically inactive pro-IL-1b, which can be released passively during cell lysis due to cytotoxicity, we examined the production of pro-IL-1b and mature-form IL-1b in both supernatants and cell lysis using immunoblotting after the cells had been infected with different strains (EDL933, DpO157, DehxA, and DehxA/pehxA). Results showed that the IL-1b in the supernatant was mainly mature-form p17 and the IL-1b in the cell lysis was mainly inactive-form pro-IL1b, as shown in Figure 4. We als.
