FIG. 2.

TNF-α-like activity released by J774A.1 cells upon infection with the Y. enterocolitica polymutant strains. Cells were infected with 20 bacteria per cell with the wild-type strain (WT), the yopB and yopP mutants as controls, the polymutant strains yopHOPEM and yopHOPEMB, and the complemented strains overexpressing yopP (yopP/P⁺⁺, yopHOPEM/P⁺⁺, and yopHOPEMB/P⁺⁺). NI, noninfected cells. TNF-α was assayed by the biological method. Results are expressed as the percentage of the maximal response and are the mean values of three separate experiments. Error bars represent the standard deviation of the three experiments. Refer to Table 1 for the identification of the strains used.